How We Should Live With Predators & Prey

BY DR STEVE CARVER

When Peter Glenser, Chairman of the BASC, wrote an article for Country Squire Magazine entitled “Custodians of the Countryside” back in November of last year I felt compelled to reply. The magazine’s editors were gracious enough to give me a “Right to Reply” for which I am grateful. A few weeks later, Liam Stokes, Head of Shooting Campaigns at the Countryside Alliance, wrote a follow-up article “In the Trenches of the Grouse Wars” for which I also penned a lengthy reply in the comments section. I haven’t yet received a response nor even an acknowledgement from either Peter or Liam. Perhaps they are too busy? It was therefore with interest and more than a wee tinge of satisfaction that I read David Eyles’ recent article on “Managing Predators and Prey” in which he takes time to reply to some of my ideas. For that David, I owe you a debt of gratitude. Thank you. But since he mentions me by name rather a lot in his article I feel duty bound, Gentleman that I am, to give him the courtesy of a reply.

1.0  Symbiosis

The sharp eyed among you will have noticed that I’ve subtly changed the title of David’s article. I’ve done this because I feel we have a moral duty to share this world with all wildlife and not just that which we feel comfortable with or is beneficial to us in some way. Ethics aside, we perhaps need to clarify a few of the points that David makes.

The implication that symbiosis involves a close physical association and a net benefit to both species is a misreading of the ecological principles that even the reference David quotes makes clear. If you dig deeper into the ecology text books, you will find that symbiosis is used to cover a range of relationships between organisms. We can break the word down into its component parts to better understand its etymological origins in the Greek. “Sym” is used to indicate togetherness as in the words ‘symmetry’ and ‘symphony’.  “Bio” obviously refers to life as in ‘biota’ or ‘biology’ and, of course, the “sis” at the end is used in converting nouns into verbs. In ecology, we distinguish several forms of symbiosis. I won’t go into them all here but they include parasitism, mutualism, commensalism, competition and, yes, predation. So, not all the relationships in symbiosis need to be beneficial to both parties.

The example David gives of a peregrine falcon killing and eating a pigeon is “predatory symbiosis” because only the predator benefits. However, ecology is never simple and here we not only have to consider the individuals but also the population and the various and complex interactions between all members of the biotic pyramid and the edaphic conditions (climate, soil, geology, topography, etc.) in which they live. Nevertheless, let us continue with the example of the peregrine and the pigeon since that is the one David provides us with.

When conditions are right, pigeon populations can expand and so the peregrines have a ready supply of food. As such, they too may expand their population in line with pigeon numbers; though this normally occurs a year or two behind the pigeons as it takes time for successful peregrine kills to be turned into eggs, chicks and fully-fledged mature peregrines. However, if the pigeon population collapses for whatever reason (it could be severe weather or lack of food supply) then the peregrine population will also decline as their prey becomes harder to find, with fewer kills making them less able to feed their hungry chicks. Thus, we see the pattern of peaks and troughs in predator and prey populations that David shows in his Figure 1, wherein predator populations closely follow the fortunes of their prey, with the predators lagging perhaps a year or two behind.

If there are more prey species than a predator population can respond to, say for example, when predators are persecuted or their habitat is destroyed, the prey population may be able to grow to such a level that it exceeds the carrying-capacity of the landscape to sustain it. At this point we may see associated environmental degradation such as crop-losses when pigeons reach ‘pest’ proportions (they seem to be particularly fond of my peas). A better example here is the deforestation and soil erosion often associated with over-grazing by deer in the absence of wolf predation. This is the example I gave Peter from Aldo Leopold’s classic essay “Thinking Like a Mountain”. Under such conditions we might also then see a commensurate collapse in prey species, since without a predator to control their numbers they effectively eat themselves out of house and home, leading to starvation and a sudden drop in population. Thus, the need for an effective control on prey populations via predation (or some other limiting factor) is often seen as the prerequisite for healthy ecosystems, benefiting both predator and prey populations alike as well as their habitat. As such, even the seemingly one-sided predator-prey relationships like that between peregrine and pigeon can regarded as beneficial to prey populations, even if a few individuals – the old, the weak, the young and the unlucky – get eaten in the process. This is the net benefit David quotes from Begon et al. (2006) and so perhaps the only dis-benefit seen in the predator-prey relationships governing game species populations is for the human predators, and not their natural ones. I refer back to Leopold’s essay at this point as I can almost hear a lot of you saying: “but humans are the top predator and we can control prey populations”. Here’s what he says…

“I now suspect that just as a deer herd lives in mortal fear of its wolves, so does a mountain live in mortal fear of its deer. And perhaps with better cause, for while a buck pulled down by wolves can be replaced in two or three years, a range pulled down by too many deer may fail of replacement in as many decades. So also with cows. The cowman who cleans his range of wolves does not realise that he is taking over the wolf’s job of trimming the herd to fit the range. He has not learned to think like a mountain. Hence we have dustbowls, and rivers washing the future into the sea.” (Aldo Leopold, 1949, “Thinking Like a Mountain” from A Sand County Almanac, OUP)

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From Aldo Leopold (1949) A Sand County Alamanc. OUP

 

2.0 Predator-Prey Relationships

At this point I’ll throw in another ecological term if I may, that of “sympatry” which is used to describe two or more species or populations that occupy the same geographical area. The word comes again from the Greek with “sym” for ‘togetherness’ and “patr” meaning ‘fatherland’. I bring this up because at the end of David’s analysis of symbiosis he seems to be saying that space, function, species distributions and their relative densities are unimportant. Au contraire mon ami! They are all important when considering predator-prey relationships and the impacts they have on species and their populations. You see predators and their presence within an ecosystem are not only vital for maintaining healthy populations of their prey species through making kills, but they are also instrumental in maintaining behavioural traits and spatial variations in feeding patterns, movement and population density. The mere presence of a predatory pressure can create a “landscape of fear” that modifies prey species’ behaviour and their distribution, and has far-reaching and often beneficial effects that can ripple across an ecosystem through another ecological process known as a “trophic cascade”. Again, the classic example is deer and their main predator the wolf. As I’m sure most of you will be aware, this has been remarkably well demonstrated in Yellowstone, about which much has been said and written. The National Geographic sums it up nicely with this Figure.

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Yellowstone before and after wolves (National Geographic Magazine, 2010)

How is this relevant to lil’ old England? Well, Peter and Liam both point out that the British landscape is heavily modified and managed by man with our keystone predators long exterminated. Yet they still bemoan the impact of too many deer (on forestry and crops) and the effect meso-predators (mustelids, corvids, etc.) have on game populations, which is why they maintain that they must be controlled if they are to have enough birds to shoot, and why management is essential to protect breeding wader populations. As with ecological models, this is an overly simplistic model that is biased towards a particular human goal; the shootable surplus. I, on the other hand, maintain that artificially high game bird populations, whether through moorland management for grouse or captive breed-and-release pheasants, is itself a significant part of the problem because it creates an imbalance in the biotic pyramid. If you constantly supress the predators in one area, you create the conditions for the over-population of their prey species which in turn simply attracts more predators from other areas and creates the spill-over predation on the non-game species that you purport to protect in managing for game. The basic ecology of symbiosis, sympatry and predator-prey relationships, together with the human modification of the landscape for agriculture and game is central to the problem. Density and function, both of which are spatially variant, are important and we ignore these at our peril.

So, no David, I have not confused my own argument, although I do concede that things are way more complex than simple models suggest, and is why I conclude that more research is needed. Since writing my reply to Peter I have been talking to as many people as I can, both on and off the moor, to see if anecdotal evidence and experience confirms my suspicions. So far it has, and that includes conversations with keepers and shoot owners as well as conservation ecologists and representatives of the game industry. It is then interesting how that after questioning my reasoning on why these basic ecological truths are relevant in the context of driven shoots, David then proceed (in the main at least) to support my ideas. Yes, things are almost always more complex than they first appear, with lag times and the effects of human land management being good examples of complicating factors, but I must thank him for being yet another land-expert who agrees with my reading of the fundamentals of the situation.

3.0 Wolves, Moose and Caribou

Isn’t it amazing how much inference one can draw from a Tweet? All I said in response to @Wayfaringhind’s posting of the Serrouya et al. (2017) study was “Lessons for driven shoots? Less intensive management, fewer game birds, fewer predators and more Red List species?” The question marks are significant. These were questions asking people ‘in the know’ whether they might confirm my hypotheses about management for game and spill-over predation. Did I mention rewilding? No, but now that David raises this in his article we can return to that later.

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I think David and I have both read different things into this paper; as @Wayfaringhind jests “It’s possible for two logical individuals to reach different conclusions based on the same set of facts”. I can see where she is coming from!

In my reading of the research, and my extrapolation of the lessons learnt to landscapes with driven shoots here in the UK, I see the introduction of vast numbers of non-native game birds (i.e. pheasants) and the intensive moorland management required to encourage shootable surpluses of wild birds (i.e. red grouse) as the equivalent of the moose and white-tailed deer seen migrating into southern British Columbia. The attraction of large numbers of meso-predators to this smörgåsbord of game birds is the equivalent of the wolf. The non-game ground nesting wader species are the mountain caribou, and thus, the spill-over predation of Red List species (curlew, plover and lapwing) is the equivalent of the secondary predation of the caribou by the wolves attracted initially by the moose.

 

4.0 Are Wolves, Moose and Caribou relevant to British Grouse Moors?

While David seems to follow my reasoning almost to the letter here we differ in one crucial aspect; he slips up and assumes that I equate predator control on UK sporting estates with culling the moose in the Canadian example. I do not. This would be the equivalent of treating the symptom rather than the cause or as Serrouya puts it…

“The band-aid solution is killing wolves, but that’s been treating the symptom. We’re trying to deal with the cause.”

In the mountains of southern BC, the cause of caribou declines has been the influx of wolves following the moose and deer. In the UK, the cause of declines in Red List ground nesting waders is (at least partly) the influx of meso-predators following the artificially high numbers of game birds on and, crucially, around sporting estates including both grouse moors and pheasant shoots. In both instances, the displacements are conflated and confused by land use change resulting in habitat loss, agri-management and climate change, but like I say, nothing in ecology is ever as simple as the models might suggest and human influences just make things harder to interpret (as well as generally making things worse).

David then goes on to mention the differences between Canada and UK game shoots, and this is where things get even more interesting.

  • Scale. Yes, size really does matter! But as a Geographer and a landscape ecologist I know that many processes scale. This is true from the physical (e.g. drainage patterns) to the ecological (e.g. predator-prey relationships). What really matters is function and the species in question. In comparing the Canadian study to UK game shoots we need to bear in mind that the species are different. Wolves hunt in packs, can roam huge areas and correspondingly their territories are large. The territorial ranges of our individual meso-predators are by comparison much smaller and, critically, in proportion to the smaller sizes of the sporting estates in which they inhabit. It is nice to see David using Wales as a size comparator (why do people always do this?) but the thing about area to edge ratio is geometrically interesting since a circle of 18,000 km2 has the same proportion of edge as a circle of only 18 km2 and even one as small as 1.8 m2. This is important because when we consider the scale of the UK and its sporting estates in comparison to the species and the predator-prey relationships operating therein, they too scale accordingly, along with the barriers to movement such as urban areas, plantation forests, motorways, agri-deserts and keepered moors. So, in terms of basic spatial ecology, we are perhaps not that much different to the mountains of southern British Columbia after all.
  • Time. The larger the animal, the longer its reproductive cycle tends to be. The critical thing here for UK sporting estates is that the game bird breeding season coincides with that of their natural predators. When Mr and Mrs Weasel have kits to feed, there are eggs and young birds to be had on the moor. When the kits are grown and have left the nest there is other prey available on the moor edge with which to fill the gap, such as rabbits, rats and mice (the effect of which must be beneficial to land management interests, yes?). The glut of ground nesting game birds and their eggs seen in the nesting season just makes sure that the predators are successful in their own critical breeding period when there are young mouths to feed, so David’s arguments about turn-over, breeding seasons and limited availability of game bird prey fall short here and are not very convincing.
  • Direct-versus-indirect control. In Canada they treat the cause, here we treat the symptom. In Canada the cause is the incoming moose population encouraging a higher wolf population and spill-over predation on the caribou, here the cause is land management for a shootable surplus, the knock-on effect of which encourages higher meso-predator populations and spill-over predation on Red List species. The more enlightened direct control would be to treat the cause and manage for reduced game bird numbers and then be satisfied with walked-up shoots and a smaller bag. The indirect control is just to treat the symptom and practice heavy-handed predator control. This exactly what Serrouya says isn’t it? Reduce the thing which is attracting the predator (the moose) rather than try to cull them (the wolves). So, better to treat the cause, rather than the symptom?
  • The differences. Ah yes, this is it. The nitty-gritty. It is all about control really. Control over nature, and some would say, control of the landed minority over the landless majority (but that’s a debate for another time). Spill-over predation is the inconvenient inconvenient truth. I say “inconvenient inconvenient” because the game lobby (CA, GWCT, BASC, etc.) often fall back on the peculiar fortunes of ground nesting birds and other species of high conservation value that have found a niche in our human-modified landscapes and micro-managed game shoots as a kind of conservation raison d’être for their primary activity of maintaining shootable surpluses of game birds. While I don’t doubt for a second that many keepers and shoot owners are deeply concerned about conserving these other non-game species, it is like I said to Liam… “shooting interests act as some kind of benevolent custodian; all seeing, all knowing, all powerful. You manage the landscape for the benefit of those species you like to shoot, accept those of no discernible economic value if they are otherwise benign, and control those that compete with you for your sport.” Curlew, plover and lapwing fall into the middle category and as such are merely a convenient side-benefit of the main concern which is the game species and generating a profit. The fact that these Red List species have become scarce in their traditional habitats due to the activities of intensive agriculture on land often owned by the very same people who tell us that their sporting activities in our uplands is essential for conserving the very species they have displaced is again another matter, but a point of some moral debate.
  • Profit. I don’t doubt David’s arguments comparing the economics of hunting in Canada with the UK game industry for a second, but I do question their relevance. His arguments about money and support for local economies are too insular for my liking. If you consider the whole equation of cost-benefits to the wider UK economy and our social well-being then we must question the sustainability of the driven shooting industry. Here I would point a questioning finger at all the downstream effects in both an economic and literal sense. I have written about this in ECOS[1] but in a nutshell, the potential ecosystem services from the UK uplands (and many a lowland one too) are perhaps far-better realised by alternative land uses to driven game shooting and all the negative externalities that it entails regardless of the limited (albeit locally important) financial benefits and the ‘sport’ of a punishingly small proportion of the UK population.

 

Conclusions

I make no secret of the fact that I am pro-wild; be that wilderness in the true sense of the word, be it wild land or be it rewilding. I’ve said so in many an article, journal paper or online blog/tweet and I’m open about the fact that I’d like to see a wilder landscape in selected areas of the UK. You could in many ways say that it has been my life’s work. I’ve been behind the mapping that enabled wild land to be included in Scottish Planning Policy[2], I’ve been involved in developing and writing policy on wilderness protection in Europe[3] and globally having co-authored the EU’s Wilderness Register and the IUCN Category 1b (wilderness) guidelines[4]. I’m proud of these achievements. Not bad for a lad from Yorkshire with only two A levels eh? But David makes another mistake in assuming that we want to rewild everywhere. We don’t. As I said to Liam “I’m far too fond of my food for that”. I also made it clear in my response to Peter’s article that I’m not against all hunting or predator control, rather it is the style and way it is undertaken that I question.

My good friend Mark Fisher has responded to David on some of these points via his blog; about the issues of ownership that lie at the hub of our relationship with the British countryside. For one, I see it as being all about control. It is what I say in my pinned Tweet: “Recent conversations underpinning my belief that land management interests don’t like rewilding ‘cos they feel threatened by lack of control.” And so, David let the cat out of the bag early on in his article when he said: “predators that interfere with numbers of the game species” …his words, not mine. Interfere. The implication being that the symbiosis between game birds and their natural predators is a natural process that he’d rather avoid and perhaps, like Liam and Peter, one that he’d rather not let on about?

I don’t pretend to have all the answers, but I am prepared to ask the awkward questions that challenge the status quo. Here I am questioning a pattern of ownership and land management that is steeped in a cultural hegemony that keeps the common folk in their place and keeps our wildlife from being, well, wild. I hear what folk say about the responsibility of land ownership, but that responsibility must extend way beyond production for personal gain, the livelihoods of tenants and ‘sport’. It must extend outwards and realise its wider social, environmental and cultural responsibilities; what Leopold called “The Land Ethic”. Food production is undeniably a top priority (we’ve got to eat) but at the same time this shouldn’t be at the expense of the wider environment and long-term sustainability. If you haven’t done so already, I would strongly recommend Leopold’s essay on the Land Ethic[5]. There is much food for thought in there on how we should live with and manage not only our predators and prey, but our land and people also.

I promised that I’d return to the topic of rewilding. Here I am very much a fan of continua. The landscape of Britain that David describes “a highly diverse patchwork quilt of woodlands, fields and open spaces on a scale which is much smaller than in many other parts of the world” is part of that continuum but one that could be so much more if we have the will and guts to make some real space for nature in amongst the bucolic ideal and not just the little bits here and there that are convenient to a certain way of thinking. This is what I call re(al)wilding[6]. It won’t be appropriate everywhere, and perhaps then only in a few selected locations when the land ownership is favourable, but we must give it a try and on a landscape scale. Less strict rewilding principles can then be applied elsewhere and on a wider basis to realise the benefits that come from greater biodiversity and natural processes such as better water quality, flood suppression, erosion control, nutrient cycling, etc. In other words, treat the cause, not the symptoms. If you want a reason for rewilding, well there it is; a Land Ethic. We just need to learn to think outside the box that is ‘direct land management for direct profit’ and adopt a more ethical and egalitarian stance that extents not just to our fellow man but to the rest of the natural world as well.

Dr Steve Carver is the Director of The Wildland Research Institute

References: 

[1]Carver, S. (2016). Flood management and nature–can rewilding help? ECOS, 37(1), 32-42. http://www.wildlandresearch.org/media/uploads/Flood-management-and-nature-ECOS-37-1.pdf
[2] http://www.snh.gov.uk/protecting-scotlands-nature/looking-after-landscapes/landscape-policy-and-guidance/wild-land/
[3] LINK
[4] https://www.iucn.org/news/protected-areas/201612/wilderness-protected-areas-management-guidelines
[5] http://rintintin.colorado.edu/~vancecd/phil3140/Leopold.pdf
[6] Carver, S. (2014). Making real space for nature: a continuum approach to UK conservation. ECOS, 35(3-4), 4-14. http://www.wildlandresearch.org/media/uploads/Making-real-space-for-nature-REVISED-VERSION-3.pdf
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