Check out: Cristescu B & Boyce MS (2013) Focusing ecological research for conservation. AMBIO, 42, 805-815.

Hi Matt, I'd also look at Graeme Caughley's (1994) article on "Directions in Conservation Biology" Journal of Animal Ecology 63 (2): 215–244. I think it's important that students realise the (potential) distinction between theory and practice - and consider how to avoid it!

On reflection, it occurred to me that my answer might not sound terribly well connected to the question about big ecological theories. However, in assessing the theory and practice of conservation, Caughley gives quite a good overview of the theoretical bases of the discipline. Off the top of my head, other big theories you might look into are Fisher's fundamental theorem (relevant to conservation genetics), metapopulation theory (relevant to population viability and landscape planning), and the tragedy of the commons (relevant to overexploitation and the need for regulation).

Hi Matt, this got me thinking. First, I assume you mean in terms of classical conservation biology, rather than adding social and economic elements and/or theories of management and stakeholder engagement. In the ecological realm I guess I would pick out key theories from different levels of biological organization. For landscapes, ideas about edge effects, matrix relevance, corridors, patch quality, relevance of habitat heterogeneity; for ecosystems, ideas about fluxes, feedbacks, cycles, alternate stable states; for communities, theories relating to gain and loss of biodiversity (insurance hypothesis, trophic cascades, intermediate disturbance, succession, food webs, competition, niche theory); for populations, theories of viability (density dependence, inbreeding, Allee effects, carrying capacity, etc.); and for individuals, theories about relevant differences between individuals (e.g., optimal foraging; sex, age and stage differences in dispersal). I'm not sure how many of these qualify as 'theories', of course, but many have substantial bodies of theory associated. There are also other theories that don't fit cleanly into this classification, such as ideas about dormancy/dispersal tradeoffs, parasites and pathogens, behavioural ecology, and invasive species. For a 3rd year course this would be too much, of course - I guess I would focus primarily on theories about biodiversity and community ecology?

That's exactly along the lines I was thinking Graeme, although I love your classification and you've included several more than I had. I'll stay clear of the socio-economic aspects as the students get a subject on this in 1st year, but lack a distinctly ecological view of conservation. Thanks all - plenty of ideas here.

Hi Matt, I agree with Philip on the importance of Caughley's article but I would like to suggest another very relevant paper by Sutherland et al.: One hundred questions of importance to the conservation of global biological diversity (Conserv Biol. 2009 Jun;23(3):557-67. doi: 10.1111/j.1523-1739.2009.01212.x). On my classes I discuss this article with undergraduate students coursing conservation biology at my University. It gives an interesting approach to several important issues on conservation biology and based on my experience students often get a good picture of the difficult tasks associated with conservation in practice.

Cheers,

JE

Hi Matt, Maybe I missed it in the above comments, but I would certainly tell your students a bit about alternate states and the consequences of positieve feedbacks and other processes that result in nonlinearities (thresholds, catastrophic shifts) thereby complicating conservation and restoration (see for example Suding et al 2004. http://dx.doi.org/10.1016/j.tree.2003.10.005).

I hope this helps.

Cheers, Jim

I like to present the following information which may throw some light on the issue of your interest. You can consult the following reference.

Som B. Ale and Henry F. Howe (2010). What Do Ecological Paradigms Offer to Conservation? International Journal of Ecology. http://dx.doi.org/10.1155/2010/250754

Other than theory of island biogeography the theory of sustainable yield is a central paradigm in the management of exploitable resources. The key assumption is that wild populations produce “excess” individuals which then can be “harvested” without diminishing the capacity of the population to maintain a more or less steady state. It's like you can live off the interest of the natural capital maintaining the deposit fixed. The ecological basis for this idea is logistic thinking. Populations reach a carrying capacity representing a number of individuals that fully use the available resources, above which population growth slows and starvation or disease take their toll. If a population has age structure, like a fish, grouse, or pine tree, births exceed deaths (the difference being the intrinsic rate of increase, and offspring cohorts overshoot carrying capacity. These are the “excess” individuals to be “harvested.” What managers must do is maintain populations at levels at or below where they produce abundant excess individuals, without depressing the population beyond recovery. An issue is whether harvest is set at some level below maximum sustainable yield as indicated by a specific projection of excess or some sustainable level below that projected level to add resilience to use. Managers must avoid exploitation to severe as to “eat the seed corn” or precipitate accidents that have the same effect.

The virtually universal concept of sustainable yield has mixed results. Its success is evident in management of game animals in North America where provincial and state governments in Canada and the United States successfully regulate small and large game populations and sport fisheries. Basic demographic estimators set limits for harvest of animals as diverse as bobwhite quail and black bear. For heavily hunted species, manipulation of the breeding system and effective breeding population such as occurs in male-only hunts for deer, allow sustainable harvest indefinitely. Targeted protection and active management can even bring some game species, like the Masked Quail in the south-western United States, back from the brink of extinction. On a larger scale, wild turkeys were hunted to 30,000 birds across the entire United States by 1900 but through active management and reintroduction now approach 7 million birds, with active hunting seasons throughout the country. Not only have sport game animals in North American avoided extinction under management for sustainable “harvest,” but most have prospered.

Commercial fisheries are managed on the same general assumption of a sustainable harvest, but with much less success. The decline in coastal fisheries began during the colonial period in North America, with the largest size classes of many species disappearing by the time biologists began keeping track in the mid-20th Century, just as industrial fisheries took hold. The absence of management may have contributed to drastic declines of many coastal fisheries, as did confounding pollution and other forms of habitat destruction.

On a global scale, however, fisheries are subjects of sophisticated management plans, international treaties, and close scrutiny in the last half of the last century to the present, yet still fall short . Twenty-four percent of 1519 fish stocks across numerous species collapsed between 1950 and 2000. Of these, 33% of the stocks showed a steady regular decline (smooth collapse), 45% fell after ups and downs (erratic collapse), and 21% appeared to be healthy, and then disappeared abruptly (plateau collapse). Smooth collapses suggest steady overexploitation, sometimes confounded by increasing environmental stress from pollution. Erratic collapses might be expected in species that fluctuate greatly in numbers from the dynamics of age structure, often confounded by external events, such as El Niño changes in water temperature that affect food resources. In such examples, harvest levels based on steady-state assumptions are bound to fail if substantial fishing pressure is applied to populations that for one reason or another are in decline or free fall at the time. Plateau collapses of sardines and herrings take place when cryptic increases in harvest efficiency occur, such as increased capture efficiencies or navigation improvements that allow concentrations of fish to be found more easily than before (i.e., regulatory definitions of fishing intensity become obsolete). Plateau collapses also occur when reduced populations show “depensatory” inability to recover, amounting to negative Allee effects manifesting in small populations. A result of sequential depletion of traditional fishing stocks is sequential exploitation of previously ignored species at lower depths, what Morato and colleagues term “fishing down the deep”, which is bound to reduce the complexity of marine food webs, thereby making ecosystems more vulnerable to damage.

Why do principles applied to sport game succeed, but fail when applied to commercial fisheries? The answers are both socio-economic and ecological. The 1992 disaster of the Canadian Grand Banks’ Atlantic cod (Gadus morhua) shows just how badly fisheries policies can go wrong, when scientists’ advice of setting lower catch quotas using less harmful fishes gear is ignored. Capital-intensive industrialized fishing fleets are politically and logistically difficult to modulate [8]. Lotka-Volterra theory might work in fisheries if instant feedback of demographic trends allowed effective regulation of the intensity of effort. It does not occur. Constant pressure on inherently stable populations often results in slow decline to collapse, and constant pressure on erratic populations leads to erratic collapse. Constant improvement in fishing technique, magnified across a large scale of effort in an industrialized fishing industry, contributes to all three patterns of collapse.

Can we learn anything from successful game management? A key difference is that sport hunting in North America is a far less intense risk to game populations than commercial fishing is to fish stocks. Strictly enforced hunting seasons, bag limits, regulations constraining equipment (e.g., cartridge limits for shotguns, bans on fully automatic rifles), and the fact that most sport hunters do not hunt from necessity ensure that a human predator is as inherently inefficient as industrial fishing fleets are inherently efficient. Relentless commercial hunting with unsophisticated firearms in tropical forests, however, is far more destructive to game populations and to the forests in which they play a role, with the key differences from sport hunting being motivation and constant hunting pressure. Demands of the markets make application of sustainable yield theory in conflict with motivations of bush-meat hunters and fishing fleets far more than with people who hunt and fish for relaxation.

Other structural differences between sport and commercial harvest may be important. Hunting seasons in the temperate zone only occupy a few days or weeks of the year, leaving a long refuge in time. Furthermore, many hunted birds or mammals also have refuges in space (e.g., parks, proximity to human habitation, and inaccessible habitats). Even the protozoa that introduced logistic thinking survive intense predation in a vial if they have refuges. Enforced regulations that ensure inefficiency distinguish sport hunting from commercial fishing or hunting, where there is a premium on increasing efficiency and refuges either do not exist or are insufficient. In this sense the suggestion by Roughgarden and Smith that harvest targets be lowered to leave more leeway for fluctuations and therefore more likelihood that “seed stocks” will be preserved, seeks to make multibillion dollar commercial fishing industry more like sport hunting or sport fishing.