Jump to content




See all Safaritalk Special Offers

Message to Guests.

Welcome to Safaritalk where we have been talking Safaris and wildlife conservation since 2006. As a guest you're welcome to read through certain areas of the forum, but to access all the facilities and to contribute your experience, ask questions and get involved, you'll need to be a member - so register here: it's quick, free and easy and I look forward to having you as a Safaritalker soon. Matt.


Photo

Predators in anthropogenic environments, an English example.


  • Please log in to reply
41 replies to this topic

#1 douglaswise

douglaswise

    Advanced Member

  • Members
  • PipPipPip
  • 420 posts
  • Local time: 04:45 PM
  • Gender:Male
  • Category 1:Tourist (regular visitor)
  • Category 2:Researcher

Posted 22 August 2016 - 05:39 PM

I have started this topic in an attempt to understand why the great majority of countrymen I know take it as axiomatic that good conservation requires some predator control whereas most urban greens seem to take the opposite view.  I have, in fact, discussed this with a few camp owners in Africa and it is their assessment that around 75% of wildlife photo-tourists fall into the latter belief category.  I can certainly sympathise - even agree - that in, some parts of Africa, wildlife reserves are sufficiently large to allow nature to sort itself out with minimal human interference.  In fact, it is to such areas that many of are drawn for their sense of remoteness as well as for their wildlife.  However, as I have expressed elsewhere in these debates, I remain uncertain that, even in such places, elephants can be allowed free rein because of their potential to damage ecosystems (unless one takes an impossibly long term view).  The greater human population densities in many parts of Africa demand, in my view, a different and more interventionist approach to wildlife conservation and good examples of this are seen, for example, in South Africa.  I am planning a trip next year to learn more about private game ranches there, including examples of those focusing on hunting and on ecotourism.  I shall be interested in stocking densities, species mixes and relative economics.  If I manage to learn anything that might be useful to readers here, I'll report back.  In the meantime, I thought it might be instructive (just as much for me as for other readers) to ruminate upon the opposing views on predator control that are so polarised in England.

 

I will start the debate by discussing matters in a theoretical way and consider various hypotheses that are used to explain predator/prey relationships.  I will then move on to consider detailed numbers that I have calculated (and which are in considerable need of refinement).  To do this, I made use of internet-gleaned information on numbers and weights of various predator and prey species followed by calculations based upon my nutritional experience to determine what weight of prey that predators must consume to sustain their numbers.  In theory, one can then work out how many prey items (depending upon prey species) are needed per predator/year.

 

THEORY

 

 1) Predator numbers are controlled by prey.

 

This is often thought to be self evident.  In fact, it only applies to specialist predators.  A prime example often given relates to the lynx/snowshoe hare, the numbers of which cycle reciprocally.  Hares have a high reproductive rate and their numbers increase rapidly until they begin to damage the potential of their food supply, at which point numbers crash.  At some point following the crash, the lynx population suffers, allowing hare numbers to increase in line with their recovering food resource.

 

2) Generalist predators and the predator trap.

 

Many predators are not dependent upon a prime prey target and can take what's available (eg the fox).  If the population of a particular prey species crashes for any reason, the predator can readily switch to alternative prey.  Due to the failure of the predator population to crash following the crash in the prey species, the population of the latter is held at a low level because numbers cannot re-build in the continuing presence of stable levels of the predator.

 

It should be noted that under both scenarios 1) and 2) it is not the predators that are initially responsible for the crashes in prey numbers.  However, it should equally be appreciated that prey cycles are not necessarily driven by food limitation.  Disease may also result in cycling (eg voles and mountain hares).  Cycling populations are generally found in prey species with high reproductive potential.  A crash of a major prey resource can also push currently available alternative prey into the predator trap through over-exploitation by predators until such time as the predator alternatives are all lowered and the predators themselves become compromised.

 

3)  Intra-guild competition.

 

Within the guild of predators, one species can compromise another by one or both of two means.  Species can deliberately set out to kill other species or otherwise drive them from their territories (eg big cats and canids in Africa).  Alternatively, one predator species can capture so much preferred prey of another species that the latter declines in numbers as a result of food resource limitation.  It is thought that intra-guild competition occurs between foxes and stoats and, certainly, between foxes and ground nesting raptors.  It is more debatable as to whether badger/hedgehog interaction can be as intra-guild competition. Certainly, badgers kill most hedgehogs they encounter, but, though the latter are themselves earthworm and nest predators, it seems more likely that badgers regard them as desirable food items rather than as potential competitors.

 

4)  Mass-dependent predation risk.

 

This hypothesis posits that predators can impact adversely on prey, not only by killing them directly, but also by influencing adversely their foraging behaviour such that they are more likely to succumb when adverse environmental conditions occur. (as example, see "Mass-dependent predation risk as a mechanism for house sparrow declines?" authored by R. McLeod et al, Biology Letters, 2006.)

 

5)  Density dependent mortality.

 

This concept proposes that a prey animal has to die for some reason.  If predation doesn't get it, starvation, disease or something else will.  The prey population as a whole won't be adversely affected because one type of death will compensated for by another.  It applies most to species with high reproductive potential (usually prey species) which are liable to run out of food or become diseased if numbers are not kept in check by predation.  However, it is possible to over-simplify.  Consider, for example, egg predation, using partridges as an example.  Partridges are capable of laying, perhaps, 30 eggs sequentially. However, they will generally stop laying and become broody after having produced a clutch of a dozen or so.  Thus, if a predator goes off with a few or even the whole of the first clutch, it won't be too damaging to the partridge population.  Chick hatching date will be later, but this will not necessarily be a problem, given the vagaries of the English weather.  If, however, nest predation occurs well into the incubation period, it is likely that the partridge won't produce a second clutch.  Of course, the predator may take the mother, plus all eggs or chicks in which case no compensation at the individual level will be possible.  Generally, English ground nesting bird species do not display density dependent mortality because they exist in areas where natural food supply is adversely impacted by man's influence and where they are already probably caught in predation traps.  However, voles probably do to the extent that, even with a good local food resource, high densities can lead to deaths through disease.  

 

From this preamble, it ought to be clear that predator/prey ratios are very complex and multifactorial.  Without very detailed research, it is impossible for one side or the other of the debate to claim either that predators are or are not not responsible for sustained declines in prey populations. One must remember that correlation does not necessarily prove causation.  It was for this reason that I thought to apply my nutritional knowledge to the problem.  I quickly determined that the results were full of guesswork.  Nevertheless, I thought them worth reporting because, as far as I know, they represent a novel approach and, further, that others may be able to contribute by challenging or refining the numbers.

 

THE NUMBERS

 

Introduction and methods:

 

I have only looked at some mammalian and avian predators (ignoring hedgehogs, rats, corvids, owls and greater spotted woodpeckers, for example. I have considered a range of prey species, but haven't included the full range (pigeons, doves, corvids)

 

For mammals, I used estimates of population numbers gleaned from a report by the Tracking Mammals Partnership (www.jncc.defra.gov.uk/pdf/pub05_ukmammals_speciesstatusText_final.pdf.  Mean body weights for males/females combined were taken from various sources.  The report only goes up to 2002.  Since then, badger numbers have increased and those of rabbits decreased (but I have ignored this).  I think the numbers I used related to adults only and didn't include young of the year.  I assume they related to the standing spring population.  My conclusions ignore young stock, and the total annual mass of prey numbers arising from multi-clutching and multi-littering.

 

For birds, I used various sources, but mainly emanating from the BTO where possible.  They quote numbers  of breeding pairs. I have doubled these and made an allowance for subdults to give an estimated number for each raptor species I have examined.  Since I haven't made any allowance for subadult mammals, I can be accused of inconsistency.

 

In calculating predator appetites, I started with the likely daily dry matter intakes, expressed as  percentages of body weights, required to satisfy energy requirements for maintenance, cost of free living and reproduction.  I then divided the numbers derived by 0.3 to convert them to fresh matter (assuming prey are 70% water) and then by 0.8 (assuming 20% waste).  I multiplied by 365 to give a number that represented the number of times/annum that a predator would consume its own body weight.  (These worked out at 33 for cats, foxes and badgers, 45 for small mustelids, 60 for buzzards and 68 for kestrels and sparrow hawks.)  The species differences are explicable by the facts that smaller species have higher metabolic rates than larger ones and that birds have higher rates than mammals.

 

Results:

 

By multiplyng the species population number by its mean body weight and then by the multiplier calculated as described above, I was able the calculate the tonnage of food eaten annually by each of the selected predators.  Thus, as an example, 200,000 foxes of mean weight of 7.0 kg, eating dry matter at the rate of 2.5% of their body weight per day (hence 33 times their weight as fresh food/annum) would collectively eat 46200 tonnes of food/annum.  In the case of the fox, clearly not all that they eat is prey so I've guessed that it is only 70% and arrived at an annual prey consumption of 32000 tonnes.  For badgers (because of earthworms and agricultural crop consumption), I have guessed that only 20% is prey (13200 tonnes).  I have combined stoats, weasels and mink as small mustelids and arrived at a total annual prey consumption  of 5130 tonnes. Equivalent tonnages for buzzards are 12000, for sparrow hawks 2244 and for kestrels 2516.  This gives an annual consumption figure of all prey for the predators considered so far of 67090 tonnes.

 

By multiplying my prey numbers by their weights, I arrived at the following figures:

 

Rabbits, 43200 tonnes.  Brown hares, 2700 tonnes. Rats, 1110 tonnes. Voles (all species), 1080 tonnes.  Mice (all species) 600 tonnes and shrews, 66 tonnes.  This totals 48756 tonnes.

 

I then made a totally wild guess at 100 million small birds of average weight 25 g to give me a further 2500 tonnes of prey. Next, I calculated the weight of pheasant and partridges released, subtracted the 40% likely to have been shot, and came up with a figure of 43000 tonnes.  To the initial 48756, I can thus add a further 45500 tonnes to give a total of 94256 tonnes.

 

Finally, I gave my attention to cats.  There are reliable data to suggest that domesticated cats bring back 84 million prey items to their their homes annually.  Unfortunately, this doesn't give any information about what is killed and not brought back. However, one can say that the weight of prey items (approx 2100 tonnes and split in number at two thirds mammals, one third birds) brought home, assuming it is eaten, only represents 2.25% of their dietary needs.  It is far more worrying to consider feral cats (up to 20% of the total cat population according to WildCRU).  I have guesstimated a figure of one million (well below 20%).  I have also taken account of the fact, maybe half, mainly in urban and suburban areas, probably receive some or all of their dietary needs from non prey items.  Nevertheless, shockingly, this still leaves a tonnage of 74250 prey items consumed by 500000 feral cats.  If my figures are close to being correct, cats-mainly feral - are consuming more weight of prey than all other predators combined.

 

Discussion:

 

I have probably greatly underestimated the tonnage of smaller prey items that are available to predators because I have worked on a standing population number and not accounted for successive generations over the year.  On the other hand, roughly half of my prey weight was made up of rabbits and hares, accessible to fewer, larger predator species which, nevertheless, also take from the pool of smaller prey species.  Furthermore, I strongly suspect that the (24 million 2002) population figure I have used for rabbits may be less after the emergence of haemorrhagic viral disease.  Possibly ironically, my figures suggest that release of game birds is assisting predators, despite keepers' attempts at control.  I have certainly underestimated badger effects because their numbers have doubled since 2002 and I haven't allowed for the fact that subadults should have been added to the adult ones.

 

I don't know whether anything useful has come out of this exercise.  I hope, however, that it will provide the framework for a vigourous debate. 

 

 


  • twaffle, pault, Africalover and 2 others like this

#2 egilio

egilio

    Advanced Member

  • Members
  • PipPipPip
  • 1,538 posts
  • Local time: 05:45 PM
  • Gender:Male
  • Category 1:Conservationist/Naturalist
  • Category 2:Ecologist

Posted 22 August 2016 - 07:30 PM

When searching for mass-dependent predation risk it's probably wise to also search for risk-effects of predation, as that's a more common term for it.

 

Here's a paper estimating the carrying capacity of African predators:

Hayward MW, Brien JO, Kerley GIH. 2007. Carrying capacity of large African predators : Predictions and tests. Biol. Conserv. 139:219–229.

LINK


Edited by egilio, 22 August 2016 - 07:30 PM.

  • twaffle likes this

#3 twaffle

twaffle

    Order of the Pith

  • Moderators
  • 8,634 posts
  • Local time: 01:15 AM
  • Gender:Female
  • Category 1:Wildlife Photographer/Artist
  • Category 2:Resident in Africa/Former resident

Posted 22 August 2016 - 11:12 PM

@douglaswise very interesting, thanks for going to that effort. It will be interesting also to see the results of your research in SA although it would be good if at some time you could also look at conservation areas with less intensive interaction as comparison. That would, however, take a lot of time and resources.

I suppose England is in a different situation to many countries being an island but also having lost its biggest predators many centuries ago. I wonder how it changed the balance of species in the long term but I guess it has been long enough to settle into a new balance.

As far as elephants are concerned it would be interesting to know how they fit into the predator/prey equation, not being either in any great sense.

Extrapolating any outcomes to the big question of the differences between urban greens and country pragmatics (or whatever one chooses to call them) is fraught with many extra levels of considerations as you no doubt know. Whatever you conclude, it will be sure to raise further debate.

Thank you, this type of post takes considerable effort.

… clarity in thought comes after challenge …


#4 egilio

egilio

    Advanced Member

  • Members
  • PipPipPip
  • 1,538 posts
  • Local time: 05:45 PM
  • Gender:Male
  • Category 1:Conservationist/Naturalist
  • Category 2:Ecologist

Posted 23 August 2016 - 12:40 AM

I've got some more time now. 

Thanks for all the effort putting into that post @douglaswise 

You put together a nice little overview of predator-prey relations and intragruild predator competition. An interesting component you haven't mentioned is individual specialization of generalist species. In some areas wild dogs main prey is kudu, in others it's impala, in others it's warthog, while all 3 prey species are present in all 3 areas. And even within the same area there can be differences. Some lion prides in Luangwa focus on puku, others on buffalo, others on hippo. If you're a warthog in the core area of a wild dog pack which specializes in kudu, you pretty safe from them. 

 

Predator-prey relations are very complex. In the field I was often asked which prey lions preferred. It's a simple short question, but very difficult to decipher. First of all you need to know have a very good idea of the complete diet of the lions. Tourists often say: "I've seen many buffalo kills, but never an impala kill" (from lions). This might make you think they prefer buffalo. But an impala is devoured within 15 minutes by a lion pride with nothing left (except horns maybe), a buffalo takes days with a considerable amount of bones left, so the chance of you finding a buffalo kill from lions is much higher. 

You could study prey contents in lion scat to determine what prey they eat, but that doesn't reveal a big part of the story.

I might prefer to eat lobster, but it's rarely available where I am so it's not reflected in any quantity in my diet. 

There is the issue of how many buffalo there are, and how many impalas. So you need to have good estimates of prey populations.

But even then. There can be 1,000 impalas and 1,000 buffaloes. That's the same number, but not the same amount of potential food. And the impalas might be in 50 groups of 20, while the buffaloes might be in 2 groups of 500. So when you randomly walk around, you're much more likely to run into an impala herd than into a buffalo herd.

So you would want to know if the lions walk around aimlessly, or are somehow visiting areas with a certain type of prey more than other areas. In order to be able to say something about this you need finescale movement data from the lions, from the prey, and also good vegetation maps. 

Another thing you need to know is how often they attack a certain type of prey. Do they attack impalas each time they encounter them? Do they attack buffalo each time they encounter them? And what does the prey do to avoid ending up as a kill? 

 

All these things need to be considered, as all of them play a role. It might be slightly off-topic here, but I think it might make you help thinking about predation.

 

One thing you might also consider is how much human waste these animals consume? Badgers, foxes do eat quite a bit of garbage.

 

A big thing is also the uncertainty in the estimates. For example here it say that domestic cats kill 92 million prey items including 57 million mammals and 27 million birds (over the period of the survey). However...these are the best estimates, the estimated number of mammals killed ranges from 52 to 63 million and the number of birds from 25 to 29 million. If you multiply estimates with estimates, but you actually take these estimates as facts (fixed numbers) you're not presenting a realistic picture. You should incorporate the uncertainty in the estimates, but when you do that on multiple levels (which you should), very quickly, the number you present will range very widely. This is annoying when you want to present a strong and compelling story, but it's better than to present a strong, compelling but wrong story. 


  • ZaminOz, Kavita, Africalover and 2 others like this

#5 douglaswise

douglaswise

    Advanced Member

  • Members
  • PipPipPip
  • 420 posts
  • Local time: 04:45 PM
  • Gender:Male
  • Category 1:Tourist (regular visitor)
  • Category 2:Researcher

Posted 23 August 2016 - 07:24 AM

@twaffle:  Thank you for your polite comments.  The article was written in part to inform myself and I am still mulling over what, if any, conclusions I can draw from it.  Clearly, it's a very crude first attempt to establish whether my "country pragmatic" views are realistic or whether they are vulnerable to attacks by "urban greens". Your coining of the term "country pragmatic" is an excellent opposite for "urban green" and, in a debate of this sort, it helps in the avoidance of more pejorative descriptions.


  • twaffle likes this

#6 douglaswise

douglaswise

    Advanced Member

  • Members
  • PipPipPip
  • 420 posts
  • Local time: 04:45 PM
  • Gender:Male
  • Category 1:Tourist (regular visitor)
  • Category 2:Researcher

Posted 23 August 2016 - 10:01 AM

@egilio:

 

Many thanks for your interest.  The link provided in post # 2 - though only providing an abstract (with the main article behind a pay wall), was a very valuable one in an African context.  I'm sure that it would make interesting reading for many "Safaritalkers".

 

I would like to comment in more detail on post # 4.

 

Your point about individual specialisation of generalist predators is well taken.  I have always assumed, possibly incorrectly, that a pack of wild dogs, for example, will choose a species of prey which is the most convenient in terms of risk/reward.  Thus, at Laikipia Wilderness Camp, I was told the local pack ate almost exclusively dikdik unless there were non-independent cubs, at which period of the year impala were hunted.  I saw warthogs being chased by the  5 month-old cubs, but I was correctly informed that there would be no serious intention to make a kill, only to run off high spirits.  Sheep, goats and cattle seemed to be safe from attack, though readily available.  We undertook some elementary mental arithmetic (of the type applied in my top post) and arrived at the, to me, surprising conclusion that the dikdik density in the area and their reported reproductive rates were adequate to allow the claimed predation level while leaving a stable population.   On reflection, I suppose choice of target species could equally well be cultural - in other words, learned behaviour over one or more generations.  However, interesting as it is, I'm not sure whether it's worth pursuing the subject further in this debate.

 

II entirely agree with you that predator/prey interactions are extremely complex.  To some extent, this is why I undertook the exercise I did.  It wasn't intended to provide precision. However, I hoped it might put bounds on further debate and establish whether it could highlight areas of conservation concern.  I deliberately didn't draw many, if any, conclusions from it because I'm still ruminating.

 

You mention that I might like to consider non-prey consumption of, say, garbage by foxes and badgers.  To some extent I did, but my calculations were, admittedly, based on fairly wild guesses.  Thus, I took the prey weight for foxes to be 70% of appetite and for badgers, 20%. 

 

You mention uncertainty in the figures.  I most sincerely hope that I haven't given the impression that my figures were certain - they are, at best, "ball park" and may well be out by several fold.  I hope, though don't know, that they aren't out by an order of magnitude.  I have mentioned my very simplistic methodology and, in some areas, highlighted weaknesses (such as using a standing weight for biomass rather than annual biomass production in calculations of availability of prey such as voles.  I have also acknowledged that my treatment of the subject is incomplete in respect of all significant predators and prey (no owls, for example).

 

I would particularly like to pick up on your criticism of my failure to use uncertainty figures for the numbers of prey items taken home by domesticated cats.  You provided a link and, in fact, it was the link I used when coming up with my 84 million figure (which should probably have been, as you say, 91 million with a lower bound of 85 if you believe the authors)  At least, by using 84 rather than 85, nobody could accuse me of other than sloppiness - certainly not of attempting to exaggerate any malign influence of cats.  However, I think you cited a bad example which may indicate that you are not be seeing "the wood for the trees".  The authors, for example, state that the UK domestic cat population is 9 million.  I don't know the source of this figure or its accuracy.  I was considering England, not the UK, but used the 84 million figure anyway.  For my purposes, it doesn't matter - it's near enough.  The cats may be killing vastly more prey than they take home and this is something the authors of the paper you cite don't appear to consider.  I don't suppose this had anything to do with any lack of integrity.  However, studies of this kind have been used by cat enthusiasts to demonstrate that their pets aren't a significant problem for wildlife.  I don't pretend to know one way or the other.  I was, however, interested to learn the wearing of bells on a collar actually reduced the cat's hunting efficiency and have always believed that owners should keep them confined overnight or, preferably, all the time.  What really shocked me were the estimates I found for feral cat numbers.  If they as great as claimed and if they are not being given artificial diets, they represent a very major menace to wildlife and every effort should be made to exterminate them.  In rural areas, this would necessitate the killing of all free ranging cats, be they domesticated or feral, because they cannot be distinguished from each other (except, possibly, if wearing belled collars).  I have always avoided killing cats on my land because I was concerned that I might be taking out my neighbours' pets.  Now, I'm beginning to wonder.

 

I would be very interested to know if you think that there are any broad conclusions that you, yourself, could draw from my efforts (other than the acknowledged fact that my numbers are extremely crude).  For what its worth, I offer a few tentative ones of my own:

 

1)  I think that many safari-goers become legitimately concerned over conservation issues relating to major African predators.  They may then often apply the same thoughts to English predators and believe they should be accorded equal levels of protection.  I think actual population numbers may therefore be educationally useful.

Thus, there are less than 50000 lions, cheetahs and wild dogs on the whole of the African Continent.  In tiny England alone, we have over half a million badgers and foxes and, now, over a quarter of a million buzzards (a near 100 fold increase  in 60 years). I know that we have no large predators left, but the populations of protected badgers and buzzards have grown hugely and are certainly now stable while the population of unprotected foxes is also stable or growing slowly despite the efforts of gamekeepers.  Meanwhile, populations of some species of song and ground nesting birds have declined markedly.  I appreciate that correlation doesn't necessarily indicate causation, but, on occasions, it may.  Of course, our rarer predators (harriers and golden eagles, for example) should be considered in a different light.  Re-introductions of such species as goshawks and red kites, made without any by your leaves to "country pragmatists", cause considerable resentment, but this might be mitigated by removal of protected status from, for example, buzzards.

 

2)  My figures suggest to me that there should be a lot more attention given to voles and conservation of their preferred habitat.  Even if I have underestimated their biomass by a factor of 4, I still think it is too low to be ideal for predators.

 

3)  It looks to me as if declines in rabbit biomass may have been more or less compensated for by increases in pheasant and partridge releases. 

 

4)  My figures suggest (no more than that) that foxes, badgers and buzzards are our major predators if one discounts feral cats.  "Country pragmatists" would have reached this conclusion anyway without the benefit of any tentative figures.  I'm not sure whether they'd be regarded by "urban greens" as a reason for a re-think.

 

5)  I am most shocked by the reported feral cat numbers.  My personal experience, albeit an extremely poor indicator, suggests to me that the numbers have been exaggerated.  However, if the cats that I not infrequently see on my small land area (35 hectares) are, in fact, feral and not neighbours' pets, I'd need to re-consider because the damage they'd be causing would probably be at least 20 times greater than I had supposed.

 

I would be interested to learn whether you think these broad conclusions are in any way justified.



#7 Towlersonsafari

Towlersonsafari

    Advanced Member

  • Members
  • PipPipPip
  • 654 posts
  • Local time: 04:45 PM
  • Gender:Not Telling
  • Location:Northamptonshire
  • Category 1:Tourist (regular visitor)
  • Category 2:---

Posted 23 August 2016 - 11:54 AM

Dear @douglaswise, it will come as no surprise to you when I say that I am against predator control for any but the most extreme cases, and i am rubbish at maths, but to add my two pennies worth, I think you need to include corvids as they do I think play  an important part as a predator, and do interact with other predators.you may want to include squirrels as they take nests and of course greater spotted  woodpeckers and herons that eat water birds and rats/small mammals especially in autumn.i think your aim is to see if a system of conservation can be used in England with predator control as a major plank to balance out the  fact that the English-and indeed UK countryside-has been so modified by man.Is it possible to divide your calculations into land types? are you just concerned with mammals and birds rather than say fish?. i have to  mention again that there is no evidence that songbird populations are affected by sparrowhawks kestrels or squirrels and that there is no correlation between song bird reductions and say the dramatic decline in raptors in the 60's. As for Red kites, as you know they are scavengers and have no real impact on prey that is not already dead.I did wonder if the increase in Red Kites was affecting  kestrels which are declining but the population maps do not support this. you are right, I think, when you say more attention needs to be paid to small mammals such as voles, and a better understanding of their requirements would go a long way to helping inform conservation policy, but that seems to suggest that prey numbers are often the deciding factor in how many predators and what area they need. As for cats, i bet you never thought you would be on the same side as Chris Packham? although again i wonder if it as simple as  saying X cats= 5 times  X prey items? just as has been pointed out  that lions prides seem to have preferred prey so do individual moggies. We had 2 brothers one who preferred rabbits rats squirrels etc and the other tried to catch birds.We had to put small fences  around the bird feeding areas to slow them down and protect our  wildlife.Finally as an example of inter-predator conflict foxes are the main predators of pine martens whilst of course cars are the main predators of badgers. I am very much enjoying your tentative thesis



#8 jeffb

jeffb

    Advanced Member

  • Members
  • PipPipPip
  • 48 posts
  • Local time: 11:45 AM
  • Gender:Male
  • Location:Maryland
  • Category 1:Tourist (first-time visitor)
  • Category 2:---

Posted 23 August 2016 - 01:14 PM

@douglaswise Thanks for posting this. Very interesting analysis.

@egilio Thanks for your responses and for the link in post #2.

 

There was an interesting article recently on a potential ecosystem service provided by the American mountain lion or cougar:

http://onlinelibrary...conl.12280/epdf

I'm not sure what this adds to your analysis, except perhaps to point out that too little predation can be as harmful as too much. But you knew that already.



#9 egilio

egilio

    Advanced Member

  • Members
  • PipPipPip
  • 1,538 posts
  • Local time: 05:45 PM
  • Gender:Male
  • Category 1:Conservationist/Naturalist
  • Category 2:Ecologist

Posted 23 August 2016 - 05:40 PM

@douglaswise I didn't mean to accuse you of anything, I merely wanted to point out that in many of those modeling exercises compounded uncertainty should be incorporated, but often isn't. You pointed out, repeatedly, that you're estimating on the safe side.

 

This shocks me:

 However, studies of this kind have been used by cat enthusiasts to demonstrate that their pets aren't a significant problem for wildlife.

 

Showing that domestic cats kills over 100 million mammals, birds, reptiles and amphibians is seen as prove that they aren't a threat to wildlife? Wow.

 

Here are my thoughts on all the numbers.

When you amount things over such a scale, you get big numbers, that doesn't necessarily mean there is a big problem. 

You write

there are less than 50000 lions, cheetahs and wild dogs on the whole of the African Continent.  In tiny England alone, we have over half a million badgers and foxes and, now, over a quarter of a million buzzards
.

 

You can't compare these two. Just because there are no lions and wild dogs in England (or lynx, wolves and bears for that matter), it doesn't mean they can be replaced by badgers and foxes in your comparison. There are millions of badgers, foxes, serval cats, caracals, genets, mongooses, hyenas, leopards, african golden cats, african wild cats, black-footed cats, sand cats, jackals, eagles, buzzards, harriers, falcons, goshawks, kites etc in Africa too. And don't forget stoats, weasels and martens in England. Likewise Africa has many prey species in size classes which are not available in England, basically anything bigger than a rabbit.

 

I might indeed be missing the trees because of the forests here. But what is there can be sustained unless it's declining continuously (thus not declining as part of natural fluctuation). Now I might be wrong, but it seems you mix up the actual carrying capacity, with the desired carrying capacity. IE, there are half a million badgers in England and they do quite well. Obviously the area they live in can sustain them. However, they might have an unwanted effect in the area they live in (whether that's true or a perception I'm not discussing here), thus they are above a desired population level/carrying capacity. If we start discussing this desired population level, we start discussing how much impact we want to tolerate from wildlife, which will quickly lead to a subjective discussion. As I'm a very tolerant person, I will refrain from that. 



#10 douglaswise

douglaswise

    Advanced Member

  • Members
  • PipPipPip
  • 420 posts
  • Local time: 04:45 PM
  • Gender:Male
  • Category 1:Tourist (regular visitor)
  • Category 2:Researcher

Posted 24 August 2016 - 12:03 PM

@jeffb:

 

Thanks for your reply.  I was interested in your link because it dealt with a situation that was more or less the obverse of that to which @egilio linked.  His concerned the conservation managers' responses to the adverse consequences of excessive predator numbers of one species to various other predator and prey species. Yours related to the potential benefits of the re-introduction of a predator species to an environment from which it was currently absent in order to reduce the adverse impacts of surplus prey. Both examples took it as axiomatic that predator numbers affect prey numbers to the probable detriment of biodiversity.  This, of course, is probably correct in the examples given because there is little evidence that mortality is likely to be (completely) density dependent in these cases. 



#11 douglaswise

douglaswise

    Advanced Member

  • Members
  • PipPipPip
  • 420 posts
  • Local time: 04:45 PM
  • Gender:Male
  • Category 1:Tourist (regular visitor)
  • Category 2:Researcher

Posted 24 August 2016 - 01:27 PM

@Towlersonsafari:

 

Thank you for reply.  I am really very excited because your comments prompted my ageing brain to recall that I have a signed copy of a book, entitled Game Heritage written by Stephen Tapper, whom I knew very well.  The book has sat on my shelves, neglected for nearly a quarter of a century.  I have just sped through it again and found that it answers in great detail many of your/questions suggestions (but, obviously only provides data up to 1990, going back to the First World War and, in some cases, before that).  I can commend it to anyone interested in this debate.  I rang the GWCT headquarters in Fordingbridge this morning to find whether it's still available.  I discovered that they still have some copies left and are selling them at the heavily discounted price of £4, due the perceived obsolescence of the contained information - this for a coffee-sized hard cover book of 140 pages, replete with illustrations, tables, graphs and references.  I would really like you to read it and report back.  In fact, I now really wish that I had re-read it before starting this debate.  It does cover corvids and does give geographical breakdowns.  Also, it shows how affairs in upland, arable and grassland ecosystems differ.  One of the things that came out for me was that numbers of keepers have reduced by over 90% from their peak, less land is keepered and the duties of low ground keepers have changed due to game bird releasing  leading to less intensity of predator control effort.  I think this is very encouraging for my support of zonal conservation and environmental offsetting in the case of raptors.

 

You state that there is "no evidence that songbird populations are affected by sparrow hawks, kestrels and squirrels."  I think you meant to suggest that there is no evidence that these predators are responsible for population declines - they are clearly affected, but it may be that the effects are minimal because mortality is density dependent.  However, causes of population declines are multifactorial and additive and difficult to tease apart (consider the predator trap and mass-dependent predation risk to which I drew attention at the start of the debate).  At a personal level, my land supports disproportionately high densities of sparrows, starlings and sparrow hawks because we breed insects by the million and some leak from our farm buildings and there are also plenty of sources of spilled grain.  Thus, "my" sparrows, for example, can thrive despite predation by sparrow hawks.  However, where food is limiting, these raptors could be pushing numbers below levels at which density dependence can compensate.  Once in the predator trap, sparrow populations could stabilise at a much lower than previous levels as their predators switch to other prey species.  When one talks of population declines one must look at short, medium and long term trends.

 

You state that "red kites are scavengers and have no real impact on prey that is not already dead). This is misleading.  Kites take live prey and the proportion in their diets will depend upon relative amounts of carrion and live prey.  They don't need carrion to survive and breed.  Their numbers are growing fast, but there is currently a lot of carrion deliberately put out for them.  I think that what you should have said is that, at current levels and in current circumstances, red kites are making no significant impacts on prey populations.

 

On a lighter note, I'll attempt to cap your story about the different food preferences of your sibling cats.  50 years ago, I hand reared two baby hedgehogs when a nest was accidentally destroyed in a muck heap.  Initially, they were bottle fed.  I then attempted to wean them on puffed wheat, milk and maggots (why, I'm not quite sure and I would have used canned cat food today).  The hoglets were soon christened Jack and Jill  - irrespective of sex which I hadn't determined. The reason was that one ate the maggots only and the other would take just the milk and puffed wheat (Like Jack Spratt and his wife who, between them, "licked their bowls clean".  (I'm not sure if younger readers will recall the nursery rhyme in which Jack wouldn't eat fat and his wife wouldn't eat lean).  I don't recall the wife as having been called Jill, but the story is already getting a bit tedious.  Suffice it to say that both animals were fenced on to the lawn when half grown in order to learn about earthworms and, one night, they escaped so I never knew their eventual fate.


  • Towlersonsafari likes this

#12 douglaswise

douglaswise

    Advanced Member

  • Members
  • PipPipPip
  • 420 posts
  • Local time: 04:45 PM
  • Gender:Male
  • Category 1:Tourist (regular visitor)
  • Category 2:Researcher

Posted 24 August 2016 - 02:22 PM

@egilio:

 

I fully appreciate that big numbers don't necessarily translate into big problems.  My summation of numbers was an initial stab at self-education.  I was attempting in a fairly rough and ready way to discover whether there were prima facie grounds to believe that there MAY be problems  and explain why "country pragmatists" assume there are and "urban greens" take an opposite view.

 

I think you may have misunderstood my intentions when I compared numbers of mesopredators in the UK with those of mega carnivores in Africa.  Perhaps, I expressed myself badly.  I was starting from the premise that rarer animals were of much more legitimate conservation concern that, say, badgers and buzzards which are, nevertheless, fully protected by law, despite the harm that, arguably, they cause in terms of economics and to other species of wildlife.

 

You may be correct to suggest that I haven't sufficiently distinguished between actual carrying capacity and desirable carrying capacity. All other things being equal, I would aim to maximise biodiversity.  However, I think this can best be achieved at least economic cost in anthropogenic environments by using a zonal model of conservation. 

 

Clearly, a continuously declining population will go extinct.  However, it is also the case that a species can continuously decline for several decades before stabilising at a much lower level.  In the UK, this could be exemplified by grey partridges and lapwings.  I am not alone in treating these lower but stable levels as undesirable and the BTO, for example, takes a similar view.

 

You suggest that the large UK badger population is doing quite well and is clearly sustaining itself before acknowledging that they may have unwanted effects in areas in which they reside.  This is quite interesting.  In my own opinion, badgers are not doing quite well in those areas of the country where their density is highest, but I'm talking about their individual welfare rather than their actual numbers.  I know you aren't too concerned about the welfare of wildlife.  I am.  For largely anthropogenic reasons, badgers in high density areas have a rich source of very patchily distributed food such that their territories have become compressed and different family groups merge into much larger groups which sett together (atypical for badgers which typically live in single family groups.) This compression has led to poorer growth, poorer reproduction and increased fighting with more severe bite wounds.  It is government policy to reduce badger densities in these areas, primarily because they spread tuberculosis to cattle ( the reciprocal is also sometimes true).  If badgers were present in less dense numbers, it is likely that tuberculosis would not be self sustaining in the species and they would become dead-end hosts as is the case for other susceptible wildlife species.  However, I may be setting off at a tangent so will stop. 



#13 egilio

egilio

    Advanced Member

  • Members
  • PipPipPip
  • 1,538 posts
  • Local time: 05:45 PM
  • Gender:Male
  • Category 1:Conservationist/Naturalist
  • Category 2:Ecologist

Posted 25 August 2016 - 02:34 AM

It is normal to see lower reproduction rates at higher densities, and it's also not uncommon that animals have different social structures at higher densities. Geckos for example can be highly territorial, but if the density get really high defending a territory isn't  possible anymore and they start living peacefully together. So it might be normal for badger to do that, it just hasn't been recorded yet as they've never been studied living at such high densities. 

Some deadly diseases need a certain minimum density of their host species to be able to sustain itself (the disease). A notable example is rabies. Infected animals die, and if the density of animals is low, infected animals will die before they can infect others. This is a dilemma with vaccination campaigns of domestic dogs in wilderness areas. Vaccinate them and the domestic dog density will go up as they will live longer and produce more, creating a possible reservoir for rabies unless all dogs are vaccinated. Don't vaccinate them and many will succumb at early ages and populations might not reach levels to sustain rabies. There will still be rabies outbreaks every now and then, but they would quickly vanish. 

As far as I know tuberculosis is a disease which develops slowly, and infected animals are contagious for a long time. Reducing badger densities probably won't have much effect on the badger-cattle infection rate. And, like you say, if badger densities are lowered, it is quite likely that badger reproduction will go up, so population growth will go up. And growing population produce more dispersers, enforced by badger habits of defending territories, which they do at those lower densities. And this dispersal increases the chance of a quicker spread of tuberculosis as there will be more badger roaming widely, coming into contact with more other badger and more cattle. 

A difficult issue!

 

More diverse ecosystems are more stable and robust to changes. Yes, some species might cause some damage, but in terms of ecosystem services intact ecosystems pay very well for themselves. In fact, the total value of services contributed annually is estimated to be several times larger than the annual GDP of ALL nations in the world combined. 



#14 Towlersonsafari

Towlersonsafari

    Advanced Member

  • Members
  • PipPipPip
  • 654 posts
  • Local time: 04:45 PM
  • Gender:Not Telling
  • Location:Northamptonshire
  • Category 1:Tourist (regular visitor)
  • Category 2:---

Posted 25 August 2016 - 07:31 AM

On a point of Badger order, the badgers in England and Wales behave a bit differently to those in  the rest of Europe including the highlands of Scotland.they do have much larger sets it is thought because the  available food can support a higher density.Although there is some evidence that in really large sets-and  I am talking about 20+ the social cohesion can break down and  the set members disperse . As for the cull, likely to be extended, this is purely as a sop to the powerful farming lobby.There is still no evidence that it has any effect, no shot badgers are tested for TB, in low TB areas cattle on cattle transmission is the highest cause of infection, Ireland has announced a change from their cull to vaccination of badgers and it is not exactly known how badger to cattle transmission occurs.A recent study shows there is no direct contact between badgers and cattle. It is likely that infected cattle can also infect badgers.Still back to the debate the thread started with



#15 douglaswise

douglaswise

    Advanced Member

  • Members
  • PipPipPip
  • 420 posts
  • Local time: 04:45 PM
  • Gender:Male
  • Category 1:Tourist (regular visitor)
  • Category 2:Researcher

Posted 25 August 2016 - 09:58 AM

@Towlersonsafari:

 

I'm more than happy to discuss badgers in great detail - I've spent very many of my free hours studying them and their role in bovine TB in the recent past. However, we are drifting off the original subject of the debate.  We could start a new debate, but I doubt its relevance to most Safaritalkers.  My e-mail address is douglas.wise@gmail.com .  If you would like to e-mail me, I would be happy to send you a stack of position papers I've written on the subject and then discuss matters from there.  



#16 douglaswise

douglaswise

    Advanced Member

  • Members
  • PipPipPip
  • 420 posts
  • Local time: 04:45 PM
  • Gender:Male
  • Category 1:Tourist (regular visitor)
  • Category 2:Researcher

Posted 25 August 2016 - 10:43 AM

@egilio:

 

Please see my reply in post #15.  I would be happy to get into badger discussions with you too, but am not convinced of its relevance to this site.  However, in passing, I agree that a one off cull of badgers would probably need to be followed by an annual 15% cull in high density areas to achieve maximum benefit. Currently, badgers and tuberculosis in cattle are costing us about £180 million/annum - shared half and half by farmers and taxpayers.  I am unaware that any country has successfully controlled TB without culling wildlife reservoirs.  I would also add that  the UK's allowed culling methods are highly inefficient.

 

Perhaps, it might be more relevant here to discuss dispersal and territorial boundaries in a more general way, particularly now that the concept of biobarriers is becoming a trendy new area of research. The idea, for the benefit of those unfamiliar with the subject, is create artificial scents to delineate territorial boundaries for certain species such as wild dogs and thus confine them within territories where their presence is beneficial or acceptable and to keep them out of other areas where human/wildlife conflicts will probably occur.  My personal feelings on the matter are largely shaped by what I have read about territorial boundaries in badgers and may not be applicable to all species.  In badgers, it is totally wrong to think of territorial boundaries as invisible fences.  They are, rather, message boards for adjacent groups.  Boar badgers frequently cross one or several successive boundaries to find mates (a high proportion of cubs are sired by boars other than that of the family group).  Young adult females also to disperse, probably to find vacant territory.  Anyway, synthetic biobarriers would seem to me to be very expensive to maintain even were they to fulfil their intended functions.

 

I found the final two sentences of your final paragraph of post #13 to be utterly astonishing.  I know it has now become trendy to put value on ecosystem services, but to suggest that the value exceeds by several fold the total GDP of all nations in the world is both astonishing and absurd.  True, we couldn't be here without a viable planet to live on, without sunlight and water, but, surely, this is becoming silly.  Perhaps, I'm misunderstanding your point. Would you care to clarify it, particularly in view of the fact that we have a rising population of 7 billion people on the planet, albeit surviving only because we have been and continue to exploit finite resources at a rate that vastly exceeds the rate at which they are replaced.



#17 jeffb

jeffb

    Advanced Member

  • Members
  • PipPipPip
  • 48 posts
  • Local time: 11:45 AM
  • Gender:Male
  • Location:Maryland
  • Category 1:Tourist (first-time visitor)
  • Category 2:---

Posted 25 August 2016 - 11:33 AM

@douglaswise and @egilio

 

I would also be interested in more detail on the total value of ecosystem services. I have to justify my research on soil microbial ecology by referring to ecosystem services provided by microbes, so this is an important topic for me, and I have not seen estimates that high.


Edited by jeffb, 25 August 2016 - 11:33 AM.


#18 Towlersonsafari

Towlersonsafari

    Advanced Member

  • Members
  • PipPipPip
  • 654 posts
  • Local time: 04:45 PM
  • Gender:Not Telling
  • Location:Northamptonshire
  • Category 1:Tourist (regular visitor)
  • Category 2:---

Posted 25 August 2016 - 12:05 PM

Yes @douglaswise it is off topic but you did raise the badger cull here.I would be most interested in reading your papers if you can point me in the direction of where they may be on the internet. to get back to your topic, and to underline what a herculean task you have set yourself, here is something from forest Enterprise Scotland commenting on  predator interaction

"Our wildlife experts are also interested that capercaillie numbers are increasing at a time when other potential predators have too. They believe that each of the predator groups are naturally keeping numbers down which in turn has had positive spin offs for the capercaillie.

Kenny continued: "We think that the various predators are controlling each other and this allows the capercaillie to thrive.  For example, goshawks are recent colonists of these woods and they are eating a lot of crows, which eat capercaillie eggs.  Similarly, foxes prey upon pine martens, which eat capercaillie eggs and young. "

Its a complicated world out there!



#19 douglaswise

douglaswise

    Advanced Member

  • Members
  • PipPipPip
  • 420 posts
  • Local time: 04:45 PM
  • Gender:Male
  • Category 1:Tourist (regular visitor)
  • Category 2:Researcher

Posted 25 August 2016 - 03:07 PM

@Towlersonsafari:

 

My papers are not on the internet.  That is why I suggested that you e-mailed me so I could send them to you as attachments.  The best I cando on the internet is to refer you to a VAWM document at www.vet-wildlifemanagement.org.uk/index.php?option=comcontent_task=view&id=14&itemid=49.  At the end of that, there is a list of submissions to government.  The first, a position statement of Nov 2015, was produced by me.  At the end of that, 6 appendices are listed which are available upon request.  It was these that I was considering sending to you.

 

Yes, I can believe capercaillie may be doing (reasonably) well in some areas of Scotland (a small upward flicker on a depressing graph) - there's enough forestry.  I have been continuously been visiting an estate in the north for over half a century where no predator control is practised.  Over the years, I've seen capercaillie, black grouse, blue hares, peregrines and hen harriers (the last 3 weeks ago).  There are also marten (which I haven't seen), foxes and of,course, corvids.  However, there isn't much of anything and the heather is deteriorating, probably because of too many sheep and no heather burning except uncontrolled crofter burns.  If you would like to see a tiny amount of a wide species range (excepting most ground nesters) and little or no estate income from the moorland, fair enough.  Go to Scotland where there's more space.  The debate I started primarily concerns England. 



#20 egilio

egilio

    Advanced Member

  • Members
  • PipPipPip
  • 1,538 posts
  • Local time: 05:45 PM
  • Gender:Male
  • Category 1:Conservationist/Naturalist
  • Category 2:Ecologist

Posted 25 August 2016 - 03:40 PM

On the value of ecosystem services. I was astonished too when I read about them the first time. But every time I read them the values are sky-rocketing high.

 

Here's one paper: http://community-wea...tanza-et-al.pdf

 

 

In 1997, the global value of ecosystem services was estimated to average $33 trillion/yr in 1995 $US ($46 trillion/yr in 2007 $US). In this paper, we provide an updated estimate based on updated unit ecosystem service values and land use change estimates between 1997 and 2011. We also address some of the critiques of the 1997 paper. Using the same methods as in the 1997 paper but with updated data, the estimate for the total global ecosystem services in 2011 is $125 trillion/yr (assuming updated unit values and changes to biome areas) and $145 trillion/yr (assuming only unit values changed), both in 2007 $US. From this we estimated the loss of eco-services from 1997 to 2011 due to land use change at $4.3–20.2 trillion/yr, depending on which unit values are used.

 

A loss of 4.3-20.2 TRILLION $$$/year due to land use change...

 

Here's another one: http://www.sciencedi...212041612000101

 

 

Acknowledging the uncertainties and contextual nature of any valuation, the analysis shows that the total value of ecosystem services is considerable and ranges between 490 int$/year for the total bundle of ecosystem services that can potentially be provided by an ‘average’ hectare of open oceans to almost 350,000 int$/year for the potential services of an ‘average’ hectare of coral reefs.

 

$350k per hectare of coral reef!

 

In many discussion, like this one, the 'damage' of a species is mentioned, but the benefits of the species aren't. Probably because they're much harder to identify, but I don't think they should be dismissed.


Edited by egilio, 25 August 2016 - 03:40 PM.






© 2006 - 2016 www.safaritalk.net - Talking Safaris and African Wildlife Conservation since 2006. Passionate about Africa.

Welcome guest to Safaritalk.
Please Register or Login to use the full facilities.