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Turtles are killed on roads, yet there is little evidence of negative road effects on their abundances. We hypothesized that this could be due to reduced predation of turtle nests laid along roadsides, which could compensate for the effects of higher adult mortality on turtle populations near roads. To test this, we quantified the relative differences in predation of artificial painted turtle (Chrysemys picta) nests near and far from roads, in a field experiment controlling for potentially confounding differences between sites. The field experiment tested the predictions that (1) nest predation rates are lower for roadside nests than nonroadside nests, (2) nest predation rates are lower for linearly placed than clumped nests, and (3) nest predation rates are lower for roadside, linearly placed nests than any other road‐adjacency and configuration combinations. We then estimated how much adult roadkill could be compensated for by reduced roadside nest predation using population viability analysis (PVA). Linearly placed roadside nests had a 26% lower predation rate than nonroad nests in a "natural" (clumped) configuration. This result, combined in a PVA with life‐history information for painted turtles, led to an estimate that approximately 3%–6% annual adult roadkill can be compensated for by reduced nest predation near roads. This suggests that compensation for adult roadkill via predation release is a plausible explanation for the previously documented lack of road effects on turtle population abundance. These results highlight the importance of considering species interactions when evaluating the effects of roads on wildlife populations. [ABSTRACT FROM AUTHOR]

Abstract Turtles are killed on roads, yet there is little evidence of negative road effects on their abundances. We hypothesized that this could be due to reduced predation of turtle nests laid along roadsides, which could compensate for the effects of higher adult mortality on turtle populations near roads. To test this, we quantified the relative differences in predation of artificial painted turtle (Chrysemys picta) nests near and far from roads, in a field experiment controlling for potentially confounding differences between sites. The field experiment tested the predictions that (1) nest predation rates are lower for roadside nests than nonroadside nests, (2) nest predation rates are lower for linearly placed than clumped nests, and (3) nest predation rates are lower for roadside, linearly placed nests than any other road‐adjacency and configuration combinations. We then estimated how much adult roadkill could be compensated for by reduced roadside nest predation using population viability analysis (PVA). Linearly placed roadside nests had a 26% lower predation rate than nonroad nests in a “natural” (clumped) configuration. This result, combined in a PVA with life‐history information for painted turtles, led to an estimate that approximately 3%–6% annual adult roadkill can be compensated for by reduced nest predation near roads. This suggests that compensation for adult roadkill via predation release is a plausible explanation for the previously documented lack of road effects on turtle population abundance. These results highlight the importance of considering species interactions when evaluating the effects of roads on wildlife populations.

If a species is bycatch in a fishery targeted at its competitor or predator, it experiences both direct anthropogenic mortality and indirect positive effects through species interactions. If the species involved interact strongly, the release from competition or predation can counteract or exceed the negative effects of bycatch. We used a set of two- and three-species community modules to analyze the relative importance of species interactions when modeling the overall effect of harvest with bycatch on a nontarget species. To measure the trade-off between direct mortality and indirect positive effects, we developed a "bycatch transition point" metric to determine, for different scenarios, what levels of bycatch shift overall harvest impact from positive to negative. Under strong direct competition with a targeted competitor, release from competition due to harvest leads to a net increase in abundance even under moderate levels of bycatch. For a three-species model with a shared obligate predator, the release from apparent competition exceeds direct competitive release and outweighs the decrease from bycatch mortality under a wide range of parameters. Therefore, in communities where a shared predator forms a strong link between the target and nontarget species, the effects of indirect interactions on populations can be larger than those of direct interactions. The bycatch transition point metric can be used for tightly linked species to evaluate the relative strengths of positive indirect effects and negative anthropogenic impacts such as bycatch, habitat degradation, and introduction of invasive species.

Ecosystem and multi-species models are used to understand ecosystem-wide effects of fishing, such as population expansion due to predation release, and further cascading effects. Many are based on fisheries models that focus on a single, depleted population, and may not always behave as expected in a multi-species context. The spawning stock recruitment (SSR) relationship, a curve linking the number of juvenile fish to the existing adult biomass, can produce dynamics that are counter-intuitive and change scenario outcomes. We analysed the Beverton–Holt SSR curve and found a population with low resilience when depleted becomes very productive under persistent predation release. To avoid implausible increases in biomass, we propose limiting recruitment to its unfished level. This allows for specification of resilience when a population is depleted, without sudden and excessive increase when the population expands. We demonstrate this dynamic and solution within an end-to-end ecosystem model, focusing on myctophids under fishing-induced predation release. We present one possible solution, but the specification of stock-recruitment models should continue to be a topic of discussion amongst multi-species and ecosystem modellers and empiricists going forward.

Ecosystem and multi-species models are used to understand ecosystem-wide effects of fishing, such as population expansion due to predation release, and further cascading effects. Many are based on fisheries models that focus on a single, depleted population, and may not always behave as expected in a multi-species context. The spawning stock recruitment (SSR) relationship, a curve linking the number of juvenile fish to the existing adult biomass, can produce dynamics that are counter-intuitive and change scenario outcomes. We analysed the Beverton–Holt SSR curve and found a population with low resilience when depleted becomes very productive under persistent predation release. To avoid implausible increases in biomass, we propose limiting recruitment to its unfished level. This allows for specification of resilience when a population is depleted, without sudden and excessive increase when the population expands. We demonstrate this dynamic and solution within an end-to-end ecosystem model, focusing on myctophids under fishing-induced predation release. We present one possible solution, but the specification of stock-recruitment models should continue to be a topic of discussion amongst multi-species and ecosystem modellers and empiricists going forward. [ABSTRACT FROM AUTHOR]

We herein review the modeling approach of Pinkerton et al. (2016, Ecol. Modelling), who tested the hypothesis that fishery depletion of large, neutrally buoyant Antarctic toothfish ( Dissostichus mawsoni ) was implicated in the recent increase in the southern Ross Sea population of Adélie penguins ( Pygoscelis adeliae ). Toothfish are a trophic competitor of penguins for Antarctic silverfish ( Pleuragramma antarctica ) in the southern Ross Sea, hence Ainley et al. (2013) and Lyver et al. (2014) proposed that the effect of the removal of toothfish was through predation release of silverfish. Pinkerton et al. concluded that predation release could not provide sufficient energy to sustain the observed penguin population growth. Critically, however, they failed to consider certain spatial and size-by-depth aspects of diet overlap, and mechanisms associated with population dynamics that could cause the population growth through predation release. In order to effectively test the prey release hypothesis, we suggest a strong inference path that incorporates what we know about population dynamics in penguins and Ross Sea food webs into life history parameterizations of penguins, toothfish and silverfish population dynamics models. [ABSTRACT FROM AUTHOR]

The Ross Sea is home to about a third of the world population of Adélie penguins ( Pygoscelis adeliae ). Between 2001 and 2013 the number of breeding pairs of Adélie penguins at colonies in the southwestern Ross Sea more than doubled. It has been suggested that this increase was caused by the fishery for Antarctic toothfish ( Dissostichus mawsoni ) leading to mesopredator release of Antarctic silverfish ( Pleuragramma antarctica ), a shared prey of toothfish and Adélie penguins. Cases of mesopredator release in marine systems have been widely reported, but limited information on marine predators often hinders quantitative investigation of these changes. The present study has brought together information from multiple models to estimate the biomass of silverfish that could be released from predation through the effects of the toothfish fishery. New diet data for toothfish are presented which show that Antarctic toothfish and Adélie penguins do not have significantly overlapping diets in the southwestern Ross Sea. The mass of silverfish released from predation due to the effects of fishing was estimated to be 128 tonnes wet-weight per year (tWW/y; 5th–95th estimation interval of 46–358 tWW/y) in 2013, equivalent to less than 2% of the biomass of silverfish estimated to be consumed annually by Adélie penguins. Even if toothfish consumed only silverfish, the predicted predation release effect would still not be sufficient to explain the observed increase in the number of Adélie penguins in the southern Ross Sea. The results of the modelling are hence inconsistent with predation release of silverfish due to the toothfish fishery being responsible for recent increases in the number of Adélie penguins breeding in the southwestern Ross Sea. [ABSTRACT FROM AUTHOR]

This article challenges Speakman's hypothesis that the modern genetic predisposition to obesity has arisen through random genetic drift in the two million years following predation release. We present evidence in support of the hypothesis that a mixture of famines and seasonal food shortages in the post-agricultural era have exerted natural selection in favour of fat storage; an effect most likely mediated through fertility, rather than viability, selection. We conclude that, far from being time to call off the search, recently developed genetic and bio-informatic methods will soon provide a definitive resolution to this long-standing ‘thrifty gene’ controversy.International Journal of Obesity (2008) 32, 1607–1610; doi:10.1038/ijo.2008.147; published online 14 October 2008 [ABSTRACT FROM AUTHOR]

Globally, bycatch in tropical/subtropical shrimp trawl and longline fisheries is threatening many marine species. Here we examine the joint effects of increased mortality caused by shrimp trawling bycatch, and reduced predation caused by losses of large sharks because of longline fishing. Research surveys in the Gulf of Mexico (1972–2002) demonstrated precipitous declines in shallow water coastal elasmobranchs where shrimping effort was highest (bonnethead 96%, Bancroft's numbfish (lesser electric ray) 98%, smooth butterfly ray > 99%) and consistent increases in deeper water elasmobranchs (Atlantic angel shark, smooth dogfish). These increases are the first empirical support for predation release caused by the loss of large sharks, which have been theorized to structure tropical/subtropical marine ecosystems. Bycatch of elasmobranchs in shrimp trawls is a critical conservation concern which is not solved by present mitigation measures; similar loss of elasmobranchs is expected to be occurring in tropical/subtropical regions worldwide where ever intensive shrimp trawling occurs. [ABSTRACT FROM AUTHOR]

Predators can impact prey via predation or risk effects, which can initiate trophic cascades. Given widespread population declines of apex predators, understanding and predicting the associated ecological consequences is a priority. When predation risk is relatively unpredictable or uncontrollable by prey, the loss of predators is hypothesized to release prey from stress; however, there are few tests of this hypothesis in the wild. A well-studied predator-prey system between white sharks ( Carcharodon carcharias ) and Cape fur seals ( Arctocephalus pusillus pusillus ) in False Bay, South Africa, has previously demonstrated elevated faecal glucocorticoid metabolite concentrations (fGCMs) in seals exposed to high levels of predation risk from white sharks. A recent decline and disappearance of white sharks from the system has coincided with a pronounced decrease in seal fGCM concentrations. Seals have concurrently been rafting further from shore and over deeper water, a behaviour that would have previously rendered them vulnerable to attack. These results show rapid physiological and behavioural responses by seals to release from predation stress. To our knowledge, this represents the first demonstration in the wild of physiological changes in prey from predator decline, and such responses are likely to increase given the scale and pace of apex predator declines globally.