Evolutionary rescue in a changing world.

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Evolutionary rescue in a changing world.

Trends Ecol Evol. 2014 Sep;29(9):521-30

Authors: Carlson SM, Cunningham CJ, Westley PA

Abstract
Evolutionary rescue occurs when adaptive evolutionary change restores positive growth to declining populations and prevents extinction. Here we outline the diagnostic features of evolutionary rescue and distinguish this phenomenon from demographic and genetic rescue. We then synthesize the rapidly accumulating theoretical and experimental studies of evolutionary rescue, highlighting the demographic, genetic, and extrinsic factors that affect the probability of rescue. By doing so, we clarify the factors to target through management and conservation. Additionally, we identify several putative cases of evolutionary rescue in nature, but conclude that compelling evidence remains elusive. We conclude with a horizon scan of where the field might develop, highlighting areas of potential application, and suggest areas where experimental evaluation will help to evaluate theoretical predictions.

PMID: 25038023 [PubMed – indexed for MEDLINE]

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Can intense predation by bears exert a depensatory effect on recruitment in a Pacific salmon population?

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Can intense predation by bears exert a depensatory effect on recruitment in a Pacific salmon population?

Oecologia. 2014 Aug 26;

Authors: Quinn TP, Cunningham CJ, Randall J, Hilborn R

Abstract
It has long been recognized that, as populations increase in density, ecological processes affecting growth and survival reduce per capita recruitment in the next generation. In contrast to the evidence for such “compensatory” density dependence, the alternative “depensatory” process (reduced per capita recruitment at low density) has proven more difficult to demonstrate in the field. To test for such depensation, we measured the spawner-recruit relationship over five decades for a sockeye salmon (Oncorhynchus nerka) population in Alaska breeding in high-quality, unaltered habitat. Twenty-five years of detailed estimates of predation by brown bears, Ursus arctos, revealed strong density dependence in predation rate; the bears killed ca. 80 % of the salmon in years of low salmon spawning abundance. Nevertheless, the reconstructed spawner-recruit relationship, adjusted to include salmon intercepted in the commercial fishery, provided no evidence of demographic depensation. That is, in years when few salmon returned and the great majority were killed by bears, the few that spawned were successful enough that the population remained highly productive, even when those killed by bears were included as potential spawners. We conclude that the high quality of breeding habitat at this site and the productive nature of semelparous Pacific salmon allowed this population to avoid the hypothesized depressed recruitment from depensatory processes expected at low density. The observed lack of demographic depensation is encouraging from a conservation standpoint because it implies that depleted populations may have the potential to rebound successfully given suitable spawning and rearing habitat, even in the presence of strong predation pressure.

PMID: 25154755 [PubMed – as supplied by publisher]

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Evolutionary rescue in a changing world.

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Evolutionary rescue in a changing world.

Trends Ecol Evol. 2014 Jul 15;

Authors: Carlson SM, Cunningham CJ, Westley PA

Abstract
Evolutionary rescue occurs when adaptive evolutionary change restores positive growth to declining populations and prevents extinction. Here we outline the diagnostic features of evolutionary rescue and distinguish this phenomenon from demographic and genetic rescue. We then synthesize the rapidly accumulating theoretical and experimental studies of evolutionary rescue, highlighting the demographic, genetic, and extrinsic factors that affect the probability of rescue. By doing so, we clarify the factors to target through management and conservation. Additionally, we identify several putative cases of evolutionary rescue in nature, but conclude that compelling evidence remains elusive. We conclude with a horizon scan of where the field might develop, highlighting areas of potential application, and suggest areas where experimental evaluation will help to evaluate theoretical predictions.

PMID: 25038023 [PubMed – as supplied by publisher]

via pubmed: school of aquatic an… http://ift.tt/1li6na6

Size selectivity of predation by brown bears depends on the density of their sockeye salmon prey.

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Size selectivity of predation by brown bears depends on the density of their sockeye salmon prey.

Am Nat. 2013 May;181(5):663-73

Authors: Cunningham CJ, Ruggerone GT, Quinn TP

Abstract
Can variation in prey density drive changes in the intensity or direction of selective predation in natural systems? Despite ample evidence of density-dependent selection, the influence of prey density on predatory selection patterns has seldom been investigated empirically. We used 20 years of field data on brown bears (Ursus arctos) foraging on sockeye salmon (Oncorhynchus nerka) in Alaska, to test the hypothesis that salmon density affects the strength of size-selective predation. Measurements from 41,240 individual salmon were used to calculate variance-standardized selection differentials describing the direction and magnitude of selection. Across the time series, the intensity of predatory selection was inversely correlated with salmon density; greater selection for smaller salmon occurred at low salmon densities as bears’ tendency to kill larger-than-average salmon was magnified. This novel connection between density dependence and selective predation runs contrary to some aspects of optimal foraging theory and differs from many observations of density-dependent selection because (1) the direction of selection remains constant while its magnitude changes as a function of density and (2) stronger selection is observed at low abundance. These findings indicate that sockeye salmon may be subject to fishery-induced size selection from both direct mechanisms and latent effects of altered predatory selection patterns on the spawning grounds, resulting from reduced salmon abundance.

PMID: 23594549 [PubMed – indexed for MEDLINE]

via pubmed: school of aquatic an… http://www.ncbi.nlm.nih.gov/pubmed/23594549?dopt=Abstract