Tag Archives: species loss

On the Loss of Large Mammals

The loss of large mammals and birds in the Pleistocene was highlighted many years ago (Martin and Wright 1967, Grayson 1977, Guthrie 1984 and many other papers). Hypotheses about why these extinctions occurred were flying left and right for many years with no clear consensus (e.g. Choquenot and Bowman 1998). The museums of the world are filled with mastodons, moas, sabre-tooth tigers and many other skeletons of large mammals and birds long extinct. The topic has come up again in a discussion of these extinctions and a prognosis of future losses (Smith et al. 2018). I do not want to question the analysis in Smith et al. (2018) but I want to concentrate on this one quotation that has captured the essence of this paper in the media:

“Because megafauna have a disproportionate influence on ecosystem structure and function, past and present body size downgrading is reshaping Earth’s biosphere.”
(pg. 310).

What is the evidence for this very strong statement? The first thought that comes to mind is from my botanical colleagues who keep reminding me that plants make of 99% of the biomass of the Earth’s ecosystems. So, if this statement is correct, it must mean that large mammals have a very strong effect on plant ecosystem structure and function. And it must also imply that large mammals are virtually immune to predators, so no trophic cascade can occur to prevent plant overgrazing.

I appreciate that it is very difficult to test such a statement since evolution has been going on for a long time before humans arrived, and so there must have been a lot of other factors causing ecosystem changes in those early years. Humans have a disproportionate love for biodiversity that is larger than us. So, we revel in elephants, tigers, bears, and whales, while at the same time we pay little attention to the insects, small mammals, most fish, and plankton. Because of this size bias, we are greatly concerned with the conservation of large animals, as we should be, but much less concerned about what is happening to the small chaps.

What is the evidence that large mammals and birds have a disproportionate influence on ecosystem structure and function? In my experience, I would say there is very little evidence for strong ecosystem effects from the collapse of the megafauna. DeMaster et al. (2006) evaluated a proposed explanation for ecosystem collapse caused by whaling in the North Pacific Ocean and concluded that the evidence was weak for a sequential megafauna collapse caused by commercial whaling. Trites et al. (2007) and Wade et al. (2007) supported this conclusion. Citing paleo-ecological data for Australia, Johnson (2010) and Rule et al. (2012) argued in another evaluation of ecosystem changes that the human-driven extinction of the megafauna in Australia resulted in large changes in plant communities, potentially confounded by climate change and increases in fire frequency about 40K years ago. If we accept these controversies, we are left with trying to decide if the current losses of large mammals are of similar strength to those assigned to the Pleistocene megafauna, as suggested by Smith et al. (2018).

If we define ecosystem function as primary productivity and ecosystem structure as species diversity, I cannot think of a single case in recent studies where this idea has been clearly tested and supported. Perhaps this simply reflects my biased career working in arctic and subarctic ecosystems in which the vast majority of the energy flow in the system rotates through the smaller species rather than the larger ones. Take the Great Plains of North America with and without the bison herds. What aspect of ecosystem function has changed because of their loss? It is impossible to say because of human intervention in the fire cycle and agricultural pre-emption of much of the landscape. It is certainly correct that overgrazing impacts can be severe in human-managed landscapes with overstocking of cattle and sheep, and that is a tragedy brought on by economics, predator elimination programs, and human land use decisions. All the changes we can describe with paleo-ecological methods have potential explanations that are highly confounded.

I think the challenge is this: to demonstrate that the loss of large mammals at the present time creates a large change in ecosystem structure and function with data on energy flow and species diversity. The only place I can see it possible to do this experimentally today would be in arctic Canada where, at least in some areas, caribou come and go in large numbers and with relatively little human impact. I doubt that you could detect any large effect in this hypothetical experiment. It is the little chaps that matter to ecosystem function, not the big chaps that we all love so much. And I would worry if you could do this experiment, the argument would be that it is a special case of extreme environments not relevant to Africa or Australia.

No one should want the large mammals and birds to disappear, but the question of how this might play out in the coming 200 years in relation to ecosystem function requires more analysis. And unlike the current political inactivity over the looming crisis in climate change, we conservation biologists should certainly try to prevent the loss of megafauna.

Choquenot, D., and Bowman, D.M.J.S. 1998. Marsupial megafauna, Aborigines and the overkill hypothesis: application of predator-prey models to the question of Pleistocene extinction in Australia. Global Ecology and Biogeography Letters 7: 167-180.

DeMaster, D.P., Trites, A.W., Clapham, P., Mizroch, S., Wade, P., Small, R.J., and Hoef, J.V. 2006. The sequential megafaunal collapse hypothesis: testing with existing data. Progress in Oceanography 68(2-4): 329-342. doi:10.1016/j.pocean.2006.02.007

Grayson, D.K. 1977. Pleistocene avifaunas and the Overkill Hypothesis. Science 195: 691-693.

Guthrie, R.D. 1984. Mosaics, allelochemics and nutrients: An ecological theory of late Pleistocene megafaunal extinctions. In: Quaternary Extinctions: A Prehistoric Revolution ed by P.S. Martin and R.G. Klein. University of Arizona Press Tucson.

Johnson, C.N. 2010. Ecological consequences of Late Quaternary extinctions of megafauna. Proceeding of the Royal Society of London, Series B 276(1667): 2509-2519. doi: 10.1098/rspb.2008.1921.

Martin, P.S., and Wright, H.E. (eds). 1967. Pleistocene Extinctions; The Search for a Cause. Yale University Press, New Haven, Connecticut. 453 pp.

Rule, S., Brook, B.W., Haberle, S.G., Turney, C.S.M., Kershaw, A.P., and Johnson, C.N. 2012. The aftermath of megafaunal extinction: ecosystem transformation in Pleistocene Australia. Science 335(6075): 1483-1486. doi: 10.1126/science.1214261.

Smith, F.A., Elliott Smith, R.E., Lyons, S.K., and Payne, J.L. 2018. Body size downgrading of mammals over the late Quaternary. Science 360(6386): 310-313. doi: 10.1126/science.aao5987.

Trites, A.W., Deecke, V.B., Gregr, E.J., Ford, J.K.B., and Olesiuk, P.F. 2007. Killer whales, whaling, and sequential megafaunal collapse in the North Pacific: a comparative analysis of the dynamics of marine mammals in Alaska and British Columbia following commercial whaling. Marine Mammal Science 23(4): 751-765. doi: 10.1111/j.1748-7692.2006.00076.x.

Wade, P.R., et al. 2007. Killer whales and marine mammal trends in the North Pacific – a re-examination of evidence for sequential megafaunal collapse and the prey-switching hypothesis. Marine Mammal Science 23(4): 766-802. doi: 10.1111/j.1748-7692.2006.00093.x.

On Caribou and Hypothesis Testing

Mountain caribou populations in western Canada have been declining for the past 10-20 years and concern has mounted to the point where extinction of many populations could be imminent, and the Canadian federal government is asking why this has occurred. This conservation issue has supported a host of field studies to determine what the threatening processes are and what we can do about them. A recent excellent summary of experimental studies in British Columbia (Serrouya et al. 2017) has stimulated me to examine this caribou crisis as an illustration of the art of hypothesis testing in field ecology. We teach all our students to specify hypotheses and alternative hypotheses as the first step to solving problems in population ecology, so here is a good example to start with.

From the abstract of this paper, here is a statement of the problem and the major hypothesis:

“The expansion of moose into southern British Columbia caused the decline and extirpation of woodland caribou due to their shared predators, a process commonly referred to as apparent competition. Using an adaptive management experiment, we tested the hypothesis that reducing moose to historic levels would reduce apparent competition and therefore recover caribou populations. “

So the first observation we might make is that much is left out of this approach to the problem. Populations can decline because of habitat loss, food shortage, excessive hunting, predation, parasitism, disease, severe weather, or inbreeding depression. In this case much background research has narrowed the field to focus on predation as a major limitation, so we can begin our search by focusing on the predation factor (review in Boutin and Merrill 2016). In particular Serrouya et al. (2017) focused their studies on the nexus of moose, wolves, and caribou and the supposition that wolves feed preferentially on moose and only secondarily on caribou, so that if moose numbers are lower, wolf numbers will be lower and incidental kills of caribou will be reduced. So they proposed two very specific hypotheses – that wolves are limited by moose abundance, and that caribou are limited by wolf predation. The experiment proposed and carried out was relatively simple in concept: kill moose by allowing more hunting in certain areas and measure the changes in wolf numbers and caribou numbers.

The experimental area contained 3 small herds of caribou (50 to 150) and the unmanipulated area contained 2 herds (20 and 120 animals) when the study began in 2003. The extended hunting worked well, and moose in the experimental area were reduced from about 1600 animals down to about 500 over the period from 2003 to 2014. Wolf numbers in the experimental area declined by about half over the experimental period because of dispersal out of the area and some starvation within the area. So the two necessary conditions of the experiment were satisfied – moose numbers declined by about two-thirds from additional hunting and wolf numbers declined by about half on the experimental area. But the caribou population on the experimental area showed mixed results with one population showing a slight increase in numbers but the other two showing a slight loss. On the unmanipulated area both caribou populations showed a continuing slow decline. On the positive side the survival rate of adult caribou was higher on the experimental area, suggesting that the treatment hypothesis was correct.

From the viewpoint of caribou conservation, the experiment failed to change the caribou population from continuous slow declines to the rapid increase needed to recover these populations to their former greater abundance. At best it could be argued that this particular experiment slowed the rate of caribou decline. Why might this be? We can make a list of possibilities:

  1. Moose numbers on the experimental area were not reduced enough (to 300 instead of to 500 achieved). Lower moose would have meant much lower wolf numbers.
  2. Small caribou populations are nearly impossible to recover because of chance events that affect small numbers. A few wolves or bears or cougars could be making all the difference to populations numbering 10-20 individuals.
  3. The experimental area and the unmanipulated area were not assigned treatments at random. This would mean to a pure statistician that you cannot make statistical comparisons between these two areas.
  4. The general hypothesis being tested is wrong, and predation by wolves is not the major limiting factor to mountain caribou populations. Many factors are involved in caribou declines and we cannot determine what they are because they change for area to area, year to year.
  5. It is impossible to do these landscape experiments because for large landscapes it is impossible to find 2 or more areas that can be considered replicates.
  6. The experimental manipulation was not carried out long enough. Ten years of manipulation is not long for caribou who have a generation time of 15-25 years.

Let us evaluate these 6 points.

#1 is fair enough, hard to achieve a population of moose this low but possible in a second experiment.

#2 is a worry because it is difficult to deal experimentally with small populations, but we have to take the populations as a given at the time we do a manipulation.

#3 is true if you are a purist but is silly in the real world where treatments can never be assigned at random in landscape experiments.

#4 is a concern and it would be nice to include bears and other predators in the studies but there is a limit to people and money. Almost all previous studies in mountain caribou declines have pointed the finger at wolves so it is only reasonable to start with this idea. The multiple factor idea is hopeless to investigate or indeed even to study without infinite time and resources.

#5 is like #3 and it is an impossible constraint on field studies. It is a common statistical fallacy to assume that replicates must be identical in every conceivable way. If this were true, no one could do any science, lab or field.

#6 is correct but was impossible in this case because the management agencies forced this study to end in 2014 so that they could conduct another different experiment. There is always a problem deciding how long a study is sufficient, and the universal problem is that the scientists or (more likely) the money and the landscape managers run out of energy if the time exceeds about 10 years or more. The result is that one must qualify the conclusions to state that this is what happened in the 10 years available for study.

This study involved a heroic amount of field work over 10 years, and is a landmark in showing what needs to be done and the scale involved. It is a far cry from sitting at a computer designing the perfect field experiment on a theoretical landscape to actually carrying out the field work to get the data summarized in this paper. The next step is to continue to monitor some of these small caribou populations, the wolves and moose to determine how this food chain continues to adjust to changes in prey levels. The next experiment needed is not yet clear, and the eternal problem is to find the high levels of funding needed to study both predators and prey in any ecosystem in the detail needed to understand why prey numbers change. Perhaps a study of all the major predators – wolves, bears, cougars – in this system should be next. We now have the radio telemetry advances that allow satellite locations, activity levels, timing of mortality, proximity sensors when predators are near their prey, and even video and sound recording so that more details of predation events can be recorded. But all this costs money that is not yet here because governments and people have other priorities and value the natural world rather less than we ecologists would prefer. There is not yet a Nobel Prize for ecological field research, and yet here is a study on an iconic Canadian species that would be high up in the running.

What would I add to this paper? My curiosity would be satisfied by the number of person-years and the budget needed to collect and analyze these results. These statistics should be on every scientific paper. And perhaps a discussion of what to do next. In much of ecology these kinds of discussions are done informally over coffee and students who want to know how science works would benefit from listening to how these informal discussions evolve. Ecology is far from simple. Physics and chemistry are simple, genetics is simple, and ecology is really a difficult science.

Boutin, S. and Merrill, E. 2016. A review of population-based management of Southern Mountain caribou in BC. {Unpublished review available at: http://cmiae.org/wp-content/uploads/Mountain-Caribou-review-final.pdf

Serrouya, R., McLellan, B.N., van Oort, H., Mowat, G., and Boutin, S. 2017. Experimental moose reduction lowers wolf density and stops decline of endangered caribou. PeerJ  5: e3736. doi: 10.7717/peerj.3736.

 

On Biodiversity and Ecosystem Function

I begin with a quote from Seddon et al. (2016):

By 2012, the consensus view based on 20 years of research was that (i) experimental reduction in species richness, at any trophic level, negatively impacts both the magnitude and stability of ecosystem functioning [12,52], and (ii) the impact of biodiversity loss on ecosystem functioning is comparable in magnitude to other major drivers of global change [13,54].”

The references are to Cardinale et al. (2012), Naeem et al. (2012), Hooper et al. (2012), and Tilman et al. (2012).

The basic conclusion of the literature cited here is that with very extensive biodiversity loss, ecosystem function such as primary productivity will be reduced. I first of all wonder which set of ecologists would doubt this. Secondly, I would like to see these papers analysed for problems of data analysis and interpretation. A good project for a graduate class in experimental design and analysis. Many of the studies I suspect are so artificial in design as to be useless for telling us what will really happen as natural biodiversity is lost. At best perhaps we can view them as political ecology to try to convince politicians and the public to do something about the true drivers of the mess, climate change and overpopulation.

Too many of the graphs I see in published papers on biodiversity and ecosystem function look like this (from Maestre et al. (2012): data from 224 global dryland plots)

There is a trend in these data but zero predictability. And even if you feel that showing trends are good enough in ecology, the trend is very weak.

Many of these analyses utilize meta-analysis. I am a critic of the philosophy of meta-analysis and not alone in wondering how useful many of these are in guiding ecological research (Vetter et al. 2013, Koricheva, and Gurevitch 2014). Perhaps the strongest division in deciding the utility of these meta-analyses is whether one is interested in general trends across ecosystems or predictability which depends largely on understanding the mechanisms behind particular trends.

Another interesting aspect of many of these analyses lies in the preoccupation with stability as a critical ecosystem function maintained by species richness. In contrast to this belief, Jacquet et al. (2016) have argued that in empirical food webs there is no simple relationship between species richness and stability, contrary to conventional theory.

Finally, another quotation from Naeem et al. (2012) which raises a critical issue on which ecologists need to focus more:

“In much of experimental ecological research, nature is seen as the complex, species-rich reference against which treatment effects are measured. In contrast, biodiversity and ecosystem functioning experiments often simply compare replicate ecosystems that differ in biodiversity, without any replicate serving as a reference to nature. Consequently, it has often been difficult to evaluate the external validity of biodiversity and ecosystem functioning research, or how its findings map onto the “real” worlds of conservation and decision making. Put another way, what light can be shed on the stewardship of nature by microbial microcosms that have no analogs in nature, or by experimental grassland studies in which some plots have, by design, no grass species? “ (page 1403)

And for those of you who are animal ecologists, the vast bulk of these studies were done on plants with none of the vertebrate browsers and grazers present. Perhaps some problems here.

Whatever one’s view of these research paradigms, no questions will be answered if we lose too much biodiversity.

Cardinale, B.J., Duffy, J.E., Gonzalez, A., Hooper, D.U., Perrings, C., Venail, P., Narwani, A., Mace, G.M., Tilman, D., Wardle, D.A., Kinzig, A.P., Daily, G.C., Loreau, M., Grace, J.B., Larigauderie, A., Srivastava, D.S. & Naeem, S. (2012) Biodiversity loss and its impact on humanity. Nature, 486, 59-67. doi: 10.1038/nature11148

Hooper, D.U., Adair, E.C., Cardinale, B.J., Byrnes, J.E.K., Hungate, B.A., Matulich, K.L., Gonzalez, A., Duffy, J.E., Gamfeldt, L. & O/’Connor, M.I. (2012) A global synthesis reveals biodiversity loss as a major driver of ecosystem change. Nature, 486, 105-108. doi: 10.1038/nature11118

Jacquet, C., Moritz, C., Morissette, L., Legagneux, P., Massol, F., Archambault, P. & Gravel, D. (2016) No complexity–stability relationship in empirical ecosystems. Nature Communications, 7, 12573. doi: 10.1038/ncomms12573

Koricheva, J. & Gurevitch, J. (2014) Uses and misuses of meta-analysis in plant ecology. Journal of Ecology, 102, 828-844. doi: 10.1111/1365-2745.12224

Maestre, F.T. et al. (2012) Plant species richness and ecosystem multifunctionality in global drylands. Science, 335, 214-218. doi: 10.1126/science.1215442

Naeem, S., Duffy, J.E. & Zavaleta, E. (2012) The functions of biological diversity in an Age of Extinction. Science, 336, 1401.

Seddon, N., Mace, G.M., Naeem, S., Tobias, J.A., Pigot, A.L., Cavanagh, R., Mouillot, D., Vause, J. & Walpole, M. (2016) Biodiversity in the Anthropocene: prospects and policy. Proceedings of the Royal Society B: Biological Sciences, 283, 20162094. doi: 10.1098/rspb.2016.2094

Tilman, D., Reich, P.B. & Isbell, F. (2012) Biodiversity impacts ecosystem productivity as much as resources, disturbance, or herbivory. Proceedings of the National Academy of Sciences 109, 10394-10397. doi: 10.1073/pnas.1208240109

Vetter, D., Rücker, G. & Storch, I. (2013) Meta-analysis: A need for well-defined usage in ecology and conservation biology. Ecosphere, 4, art74. doi: 10.1890/ES13-00062.1

On Conservation

The question of how ecology can guide decisions about conservation actions is a vexed one of which much has already been written with respect to conservation triage (Bottrill et al. 2009, Gerber 2016). The global question – what should we do now? – produces two extreme answers: (1) do nothing. The biodiversity on earth has gone through many climatic fluctuations imposed by geology and planetary physics and these forces are out of our hands. Or (2) we must protect all species because we do not know if they are important for ecosystem function. The government recognizes that (2) is impossible, and either reflects back to answer (1) or politely asks scientists to suggest what is possible to achieve with limited funding. John Wiens (2016) in an interesting discussion in the British Ecological Society Bulletin (December 2016, pp 38-39) suggests that two possible solutions to this conundrum are to get more funding for conservation to reduce this clear financial limitation, or secondly to move from the conservation of individual species to that of ecosystems. The problem he and many others recognize is that the public at large fall in love with individual species much more readily than with ecosystems. It is the same problem medical science often faces with contributions from wealthy people – attack individual diseases with my funding, not public health in general.

Ecologists face this dilemma with respect to their research agenda and research grants in general – what exactly can you achieve in 3-5 years with a small amount of money? If your research is species-specific, something useful can often be studied particularly if the threatening processes are partly understood and you adopt an experimental approach. If your research is ecosystem oriented and your funds are limited you must generally go to the computer and satellite ecology to make any short term research possible. This problem of larger scale = larger costs can be alleviated if you work in a group of scientists all addressing the same ecosystem issue. This still requires large scale funding which is not as easily obtained as ecologists might like. The government by contrast wishes more and more to see results even after only a few years, and asks whether you have answered your original question. The result is a patchwork of ecological data which too often makes no one happy.

If you want a concrete example, consider the woodland caribou of western Canada (Schneider et al. 2010). For these caribou Hebblewhite (2017) has clearly outlined a case in which the outcomes of any particular action are difficult to predict with the certainty that governments and business would be happy with. Many small herds are decreasing in size, and one path is to triage them, leaving many small herds to go extinct and trying to focus financial resources to save larger herds in larger blocks of habitat for future generations. The problem is the oil and gas industry in western Canada, and hence the battle between resources that are worth billions of dollars and a few caribou. Wolf control can serve as a short term solution, but it is expensive and temporary. Governments like action even if it is of no use in the long term; it makes good media coverage. None of these kinds of conservation decisions are scientific in nature, and must be policy decisions by governments. It flips us back into the continuum between options (1) and (2) in the opening paragraph above. And for governments policy decisions are more about jobs and money than about conservation.

The list of threatened and endangered species that make our newspapers are a tiny fraction of the diversity of species in any ecosystem. There is no question but that many of these charismatic species are declining in numbers, but the two larger questions are: will this particular species go extinct? And if this happens will this make any difference to ecosystem function? There is scarcely a single species of all that are listed as threatened and endangered for which ecologists have a good answer to either of these questions. So the fallback position to option (1) is that we have a moral obligation to protect all species. But this fallback position leads us even further out of science.

In the end we must ask as scientists what we can do with the understanding we have, and what more needs to be done to improve this understanding. Behind all this scientific research looms the elephant of climate change which we either ignore or build untestable computer models to make ‘predictions’ which may or may not occur, if only because of the time scales involved.

None of these problems prevents us from taking actions on conservation on the ground (Wiens 2016a). We know that, if we take away all the habitat, species abundances will decline and some will go extinct. Protecting habitat is the best course of action now because it needs little research to guide action. There is much to know yet about the scale of habitats that need preservation, and about how the present scale of climate change is affecting protected areas now. Short term research can be most useful for these issues. Long-term research needs to follow.

Bottrill, M.C., et al. (2009) Finite conservation funds mean triage is unavoidable. Trends in Ecology & Evolution, 24, 183-184. doi: 10.1016/j.tree.2008.11.007

Gerber, L.R. (2016) Conservation triage or injurious neglect in endangered species recovery. Proceedings of the National Academy of Sciences USA, 113, 3563-3566. doi: 10.1073/pnas.1525085113

Hebblewhite, M. (2017) Billion dollar boreal woodland caribou and the biodiversity impacts of the global oil and gas industry. Biological Conservation, 206, 102-111. doi: 10.1016/j.biocon.2016.12.014

Schneider, R.R., Hauer, G., Adamowicz, W.L. & Boutin, S. (2010) Triage for conserving populations of threatened species: The case of woodland caribou in Alberta. Biological Conservation, 143, 1603-1611. doi: 10.1016/j.biocon.2010.04.002

Wiens, J.A. (2016) Is conservation a zero-sum game? British Ecological Society Bulletin 47(4): 38-39.

Wiens, J.A. (2016a) Ecological Challenges and Conservation Conundrums: Essays and Reflections for a Changing World. John Wiley and Sons, Hoboken, New Jersey. 344 pp. ISBN: 9781118895108

Is Conservation Ecology a Science?

Now this is certainly a silly question. To be sure conservation ecologists collect much data, use rigorous statistical models, and do their best to achieve the general goal of protecting the Earth’s biodiversity, so clearly what they do must be the foundations of a science. But a look through some of the recent literature could give you second thoughts.

Consider for example – what are the hallmarks of science? Collecting data is one hallmark of science but is clearly not a distinguishing feature. Collecting data on the prices of breakfast cereals in several supermarkets may be useful for some purposes but it would not be confused with science. The newspapers are full of economic statistics about this and that and again no one would confuse that with science. We commonly remark that ‘this is a good scientific way to go about doing things” without thinking too much about what this means.

Back to basics. Science is a way of knowing, of accumulating knowledge to answer questions or problems in an independently verifiable way. Science deals with questions or problems that require some explanation, and the explanation is a hypothesis that needs to be tested. If the test is retrospective, the explanation may be useful for understanding the past. But science at its best is predictive about what will happen in the future, given a set of assumptions. And science always has alternative explanations or hypotheses in case the first one fails. So much everyone knows.

Conservation ecology is akin to history in having a great deal of information about the past but wishing to use that information to inform the future. In a certain sense it has a lot of the problems of history. History, according to many historians (Spinney 2012) is “just one damn thing after another”, so that there can be no science of history. But Turchin disagrees (2003, 2012) and claims that general laws can be recognized in history and general mathematical models developed. He predicts from these historical models that unrest will break out in the USA around 2020 as cycles of violence have broken out in the past every 30-50 years in this country (Spinney 2012). This is a testable prediction in a reasonable time frame.

If we look at the literature of conservation ecology and conservation genetics, we can find many observations of species declines, of geographical range shifts, and many predictions of general deterioration in the Earth’s biota. Virtually all of these predictions are not testable in any realistic time frame. We can extrapolate linear trends in population size to zero but there are so many assumptions that have to be incorporated to make these predictions, few would put money on them. For the most part the concern is rather to do something now to prevent these losses and that is very useful research. But since the major drivers of potential extinctions are habitat loss and climate change, two forces that conservation biologists have no direct control over, it is not at all clear how optimistic or pessimistic we should be when we see negative trends. Are we becoming biological historians?

There are unfortunately too few general ‘laws’ in conservation ecology to make specific predictions about the protection of biodiversity. Every one of the “ecological theory predicts…” statements I have seen in conservation papers refer to theory with so many exceptions that it ought not to be called theory at all. There are some certain predictions – if we eliminate all the habitat a species occupies, it will certainly go extinct. But exactly how much can we get rid of is an open question that there are no general rules about. “Protect genetic diversity” is another general rule of conservation biology, but the consequences of the loss of genetic diversity cannot be estimated except for controlled laboratory populations that bear little relationship to the real world.

The problems of conservation genetics are even more severe. I am amazed that conservation geneticists think they can decide what species are most ‘important’ for future evolution so that we should protect certain clades (Vane-Wright et al. 1991, Redding et al. 2014 and much additional literature). Again this is largely a guess based on so many assumptions that who knows what we would have chosen if we were in the time of the dinosaurs. The overarching problem of conservation biology is the temptation to play God. We should do this, we should do that. Who will be around to pick up the pieces when the assumptions are all wrong? Who should play God?

Redding, D.W., Mazel, F. & Mooers, A.Ø. (2014) Measuring evolutionary isolation for conservation. PLoS ONE, 9, e113490.

Spinney, L. (2012) History as science. Nature, 488, 24-26.

Turchin, P. (2003) Historical dynamics : why states rise and fall. Princeton University Press, Princeton, New Jersey.

Turchin, P. (2012) Dynamics of political instability in the United States, 1780–2010. Journal of Peace Research, 49, 577-591.

Vane-Wright, R.I., Humphries, C.J. & Williams, P.H. (1991) What to protect?—Systematics and the agony of choice. Biological Conservation, 55, 235-254.

Are Birds of Any Consequence?

We all love birds. They are colourful, interesting creatures and they entice many people to a love of nature and then hopefully the conservation of biodiversity. Thus we do not want to get rid of them. A great deal of effort goes into censusing birds and they are often thought of as indicator species of ecosystem health. No one is in favour of ‘Silent Spring’. But let us do a thought experiment.

The question I wish to ask is somewhat different than the important issue of bird conservation: are birds of any consequence to the operational integrity of communities and ecosystems? In the simplest case what would happen, say, to the eastern deciduous forest or the tall grass prairie or the arctic tundra if all the birds in those ecosystems went extinct? Predators that specialize on birds would clearly disappear but I do not know how many bird specialist predators exist. At the same time the parasites of these birds would be gone. But what about the integrity of existing ecosystems?

Can we dismiss the oceans because birds have a negligible effect on oceanic food webs and energy flow? I do not know the answer to this. In forests birds are often thought to keep insect pests of trees under control, but this seems to be unlikely in many systems in which defoliating insects damage trees of many sorts. Perhaps insect outbreaks would increase in frequency if there were no birds. I come away with the image that birds are for the most part of little consequence for terrestrial ecosystems because they are consumers operating at a very low quantitative level. An exception might be tropical forests in which birds are essential pollinators and seed dispersers, but again I am not sure how often they are necessary pollinators or seed dispersers.

All of this speculation is pretty useless, one might argue, because birds are not going to disappear. They may well be reduced in abundance if habitat is lost and habitat loss seems to be a global problem. But there are two aspects of current ecological research that these idle speculations touch on. First, are birds very good model systems for conservation biology? The answer the ecological world seems to have decided is that they are and very much research must be done on birds for this reason. If research time and money is limited, more research on birds means less on other aspects of community and ecosystem dynamics. Should we be concerned about this? Bird research is convenient and sexy, at least in university settings, but is it more of “Nero fiddling while Rome is burning”? One might in fact argue that many birds are the worst possible model system for understanding conservation problems except for those specific to birds. When I was producing a textbook section on population dynamics I tried to find a good solid example of a supposed decline in bird abundance for any species in which the mechanisms of decline were understood. While there are many data on declines, and much hand wringing, there were virtually no examples with hard data on mechanisms except for the vague idea of habitat loss. Maybe mechanisms are unimportant in conservation biology but it seems unlikely that they are superfluous to understanding the larger issues of population dynamics.

The second general question is the converse one of what kinds of organisms should ecologists be concentrating on if we are to make convincing arguments about biodiversity conservation? If changes in community and ecosystem dynamics are looming, so that the future will not look like the past, where should we put our energies to prevent ecosystem collapse? Are insects and invertebrates in general of greater importance that birds or mammals?

Hurlbert (1971, 1997) raised the question of how to determine the general functional importance of a species to a community, and he concluded that the only measure that has been put forward is ‘the sum over all species, of the changes in productivity which would occur on removal of the particular species from the community’. He pointed out that this definition of importance is clear and specific but could never be measured for even a single species in a community for practical reasons. Hurlbert (1997) also recognized that ‘importance’ had now morphed into ‘keystone’ for much of ecology (e.g. Daily et al. 1993), with all the problems associated with the keystone idea. He suggested, as did Walker (1992) that most species are redundant and of little consequence to ecosystem functioning. Much discussion has occurred since these papers and some has morphed into discussions of ‘functional groups’ instead of species. But plant ecologists have in general not addressed the challenges that Hurlbert (1999) asked, and we are far from being able to answer even the hypothetical question in the title of this blog.

Daily, G.C., Ehrlich, P.R., and Haddad, N.M. 1993. Double keystone bird in a keystone species complex. Proceedings of the National Academy of Sciences USA 90(2): 592-594. doi:10.2307/2361101.

Hurlbert, S.H. 1971. The non-concept of species diversity: a critique and alternative parameters. Ecology 52: 577-586.

Hurlbert, S.H. 1997. Functional importance vs. keystoneness: Reformulating some questions in theoretical biocenology. Australian Journal of Ecology 22(4): 369-382.

Walker, B.H. 1992. Biodiversity and ecological redundancy. Conservation Biology 6: 18-23.

Wildlife Management Dilemmas

The science of wildlife management has moved from the good old days of worrying only about deer and ducks to the broader issues of conservation management of all species. But it operates in an impossible squeeze between human activities and wildlife responses. One key problem is the incremental creep of land use decisions. If we log half of the forest surely there is plenty left there for the wildlife to thrive, or so many people believe. So a central dilemma is habitat loss. The simple approach using ‘cow arithmetic’ says that if you have a farm one-third the size of what you have now, you will be able to have only one-third the number of cows. So habitat loss is critical but there seems to be no way of stopping it as long as the human population continues to expand.

To solve this problem we set up parks and reserves. That will please most of the botanists because if you have a plant species you are concerned about, you need set aside only a few hectares of land to keep it safe. This approach is at the core of wildlife management’s dilemma. You keep the plant species but lose the ecosystem. Certainly you can keep many of the small insects in a few hectares, so you protect not only the plant species but more of the biota. But you will lose all the birds and the larger species that need much larger areas of habitat. One of the defining moments in wildlife management and conservation ecology occurred when several ecologists recognized that even large national parks were not large enough for the charismatic megafauna.

Maybe we can rescue it all with metapopulations, islands of good habitat close enough to each other to permit dispersal. That will work in some cases and is a useful addition to the management arsenal of tools. But then we have to cope with additional problems – introduced pests and diseases that we may or may not be able to control, and global problems of air and water pollution that respect no neat geographic boundaries.

We cannot control species interactions so if we tinker with one aspect of the ecosystem, we find unintended consequences in another aspect of the ecosystem that we did not expect. We brought rabbits to Australia and to many islands with dire consequences no one seemed to anticipate. We also brought rats and pigs to island inadvertently with many well documented problems for bird and plants. We take predators away from ecosystems and then complain to the government that there are too may deer or Canada geese.

So part of the dilemma of wildlife management in the 21st century is that we do XYZ and then only later ask ecologists whether it was a good idea or not to do XYZ. Decisions are made by governments, companies, farmers, or city dwellers to change some element of the ecosystem without anyone asking a wildlife manager or an ecologist what the consequences might be. We love cats so we pass laws that prohibit managers from culling wild cats and only allow them to sterilize and release them. We love horses so we do the same. So wildlife management decisions are driven not by ecological studies and recommendations but by public demands and weak politicians. Wildlife management is thus a social science, with all the dilemmas generated when one part of society wishes to harvest seals and one part demands protection for seals.

Wildlife management has always been handicapped by the hunters and fishers who know everything about what management should be practiced. There is no need to have any professional training to decide management goals, management actions, and funding preferences for many of these people. I suppose we should at least be grateful that the same approach is not applied in medical science.

Wildlife management has always been a low priority activity, underfunded and moved more by political whims than by science. This is not at all the fault of all the excellent wildlife and fishery scientists who try their best to protect and manage our ecosystems. It is a victim of the constraints of making decisions on the spot about long term issues without the time or money to investigate the science necessary for knowledge of the consequences of our actions. The world changes slowly and if our memory is on the time span of 1-3 years, we are not on ecosystem time.

Much action must be spent on trying to restore ecosystems damaged by human activities. Restoration ecology recognizes that it is really partial restoration ecology because we cannot get back to the starting point. None of this is terribly new to ecologists or wildlife managers but it is good to keep it in mind as we get lost in the details of our daily chores.

Humans are destroying the earth in their quest for wealth, and simultaneously producing the problems of poverty and obesity. Led by politicians who do not lead and who do not seem to know what the problems of the Earth are, we keep a positive view of the scientific progress we generate, enjoy the existing beauty of biodiversity, and hope that the future will somehow cope with the changes we have set in motion.

“Humans, including ecologists, have a peculiar fascination with attempting to correct one ecological mistake with another, rather than removing the source of the problem”.   (Schindler 1997, p. 4)

 

Estes, J.A. et al. 2011. Trophic downgrading of Planet Earth. Science 333:301-306.

Likens, G.E. 2010. The role of science in decision making: does evidence-based science drive environmental policy? Frontiers in Ecology and the Environment 8:e1-e9.

Newmark, W.D. 1985. Legal and biotic boundaries of Western North American National Parks: A problem of congruence. Biological Conservation 33:197-208.

Pauly, D. 1995. Anecdotes and the shifting baseline syndrome of fisheries. Trends in Ecology and Evolution 10:430.

Schindler, D. W. 1997. Liming to restore acidified lakes and streams: a typical approach to restoring damaged ecosystems? Restoration Ecology 5:1-6.

 

On Biodiversity Science

Biodiversity science features heavily in articles in Science and Nature and it is a good idea to look at the accumulated wisdom to date. We can begin with the Cardinale et al. (2012) paper in Nature (“Biodiversity Loss and Its Impact on Humanity”) which gives us six consensus statements:

Consensus statement one: There is now unequivocal evidence that biodiversity loss reduces the efficiency by which ecological communities capture biologically essential resources, produce biomass, decompose and recycle biologically essential nutrients.

Consensus statement two: There is mounting evidence that biodiversity increases the stability of ecosystem functions through time.

Consensus statement three: The impact of biodiversity on any single ecosystem process is nonlinear and saturating, such that change accelerates as biodiversity loss increases.

Consensus statement four: Diverse communities are more productive because they contain key species that have a large influence on productivity, and differences in functional traits among organisms increase total resource capture.

Consensus statement five: Loss of diversity across trophic levels has the potential to influence ecosystem functions even more strongly than diversity loss within trophic levels.

Consensus statement six: Functional traits of organisms have large impacts on the magnitude of ecosystem functions, which give rise to a wide range of plausible impacts of extinction on ecosystem function.

followed by four emerging trends:

Emerging trend one: The impacts of diversity loss on ecological processes might be sufficiently large to rival the impacts of many other global drivers of environmental change.

Emerging trend two: Diversity effects grow stronger with time, and may increase at larger spatial scales.

Emerging trend three: Maintaining multiple ecosystem processes at multiple places and time requires higher levels of biodiversity than does a single process at a single place and time.

Emerging trend four: The ecological consequences of biodiversity loss can be predicted from evolutionary history.

I encourage you to read this paper and consider how well it describes a blueprint of past and future research on biodiversity. Here I offer a few thoughts on why I think it consists of a set of worrisome generalizations.

First of all every biologist would like to think that biodiversity is important. But we should consider what the equivalent statement might be for chemistry – chemicals are important. Surely this is both true and of little use, since we can never define scientifically the word ‘important’. Biodiversity is so broadly defined as to be a rather poor noun to use in scientific statements unless it is strictly defined. But you can take any kind of biodiversity measure – species number (richness) for example, and you might find that species X is a terrible weed that is not desirable for farmers but is beautiful in your home garden or useful food for butterflies. Malaria-carrying mosquitoes are not particularly desirable members of the local biological community. But let us all agree that biodiversity is important because it is an ethical belief but not a scientific statement as it stands.

If we look at the consensus statements as scientific hypotheses (I note the word ‘hypothesis’ appears only once in this article), we can ask how you could test them and what the alternative hypotheses would be. For consensus 1 for example, what would be the result of finding a community that increased productivity if certain species were lost from the system? This finding would not be viewed as contrary to consensus one because it would be said that the increased productivity was not done efficiently. It is probably best to assume these statements are not hypotheses to be tested.

As we work our way through the consensus statements, we find they are filled with weasel words that are useful in eliminating contrary evidence. Thus for consensus statement 2 we can stop at biodiversity (many definitions) and then stability (perhaps 70 different metrics) and finally ecosystem functions (of which there are many) and time (weeks?, years?, centuries?). The consensus which sounds so solid is empirically rather empty as any guide to the world.

I am left with many questions. Could not all of these consensus statements have been written 30 years ago? All of them have contrary instances that could be given from the literature, if the terms were rigorously defined. But this many not matter. Let us concede that these generalizations may be right 90% of the time. The bottom line is that we should conserve biodiversity. But this is what everybody has been saying for decades so we are no farther ahead.

The singular problem that concerns me the most is that these kinds of consensus statements are of little use to the land manager or the wildlife manager or the politician who has to make applied decisions at the local level. If we wish to arrest the decline of a particular songbird, what is the utility of these kind of statements? I have concluded that these kinds of papers about biodiversity are a kind of pablum for conservation ecologists to show that Nature and Science really are concerned about conservation issues while at the same time they devote 97% of their issues to the technological fixes that will ‘solve’ all the problems conservation biologists continually point out. As such these kinds of papers are useful statements for political ecology.

The four emerging trends are themselves worthy of another blog. They are vague ideas expressing beliefs that cannot be considered scientific hypotheses without rigorous definitions, and in their present form are almost quasi-religious statements of belief. How they might ever be tested is unclear. I particularly enjoyed the fourth emerging trend since I think that one of the evolutionary laws is that evolutionary history is exactly that – history – not a predictive map of future changes. There is a certain irony of our time that some of the world’s most prestigious evolutionary biologists are anti-religion while biodiversity scientists are trying hard to set up a new religion of biodiversity beliefs.

Cardinale, B. J.et al. 2012. Biodiversity loss and its impact on humanity. Nature 486:59-67.