Effects of Social Structure and Prey Dynamics on Extinction Risk in Gray Wolves

Extinction models based on diffusion theory generally fail to incorporate two important aspects of population biology—social structure and prey dynamics. We include these aspects in an individual-based extinction model for small, isolated populations of the gray wolf (Canis lupus). Our model predicts mean times to extinction significantly longer than those predicted by more general (diffusion) models. According to our model, an isolated population of 50 wolves has a 95% chance of surviving just 9 years and only a 30% chance of surviving beyond 100 years. Reflecting the influence of social structure, a wolf population initially comprising 50 individuals is expected to persist only a few years longer, on average (71 years), than is a population initially comprising just a single reproductive pair (62 years). In contrast, substantially greater average prey abundance leads to dramatically longer expected persistence times. Autocorrelated prey dynamics result in a more complex distribution of extinction times than predicted by many extinction models. We contend that demographic stochasticity may pose the greatest threat to small, isolated wolf populations, although environmental stochasticity and genetic effects may compound this threat. Our work highlights the importance of considering social structure and resource dynamics in the development of population viability analyses.     

不同碳源条件下草菇内切型纤维素酶基因（eg1）转录表达的分析

利用Northernblot方法分析了不同碳源条件下草菇切型纤维素酶基因(eg1)的表达.结果发现,在含有纤维素的液体培养基中生长10d,eg1在草菇菌丝中有高效表达;纤维二糖、α-乳糖、β-乳糖,也能诱导eg1的表达,但和纤维素相比,eg1的表达量相对较低,并且它们的诱导效应在加入这类糖12h后迅速减弱;槐糖和龙胆二糖的诱导作用非常弱.在天然稻草为基质的固体栽培料生长时,草菇eg1的表达和草菇菌丝生长与出菇相对应,在菌丝生长期(d8)可见eg1的表达,d12时菌丝已长满,表达减弱,在出菇及菇体的分化及增大期,eg1的表达量逐渐增强,在成熟期达到最高水平;表明在草菇菇体发育中需要更多碳源及能源的补充,eg1在这方面起着非常重要的作用.图4参14     

Mercury concentrations in deer mouse (Peromyscus maniculatus) tissues from Isle Royale National Park.

We used deer mice (Peromyscus maniculatus) to investigate variation in mercury exposure across the terrestrial ecosystem of Isle Royale National Park (Michigan, USA). Although previous work suggested that mercury (Hg) levels may be higher inside the Sargent Lake watershed of Isle Royale than outside the watershed, Hg concentrations in livers were higher outside the Sargent Lake watershed (100.13 ng Hg/g dry tissue) than inside the watershed (35.50 ng Hg/g dry tissue; P = 0.06). Mercury levels in kidneys did not differ significantly (P = 0.57) between samples collected outside (443.23 ng Hg/g dry tissue) and inside (360.62 ng Hg/g dry tissue) the Sargent Lake watershed. Mean Hg concentrations in the livers of mice at some sites in Isle Royale are not significantly lower (P = 0.62) than Hg concentrations considered by some government agencies to be unhealthy for human consumption. Although Hg concentrations in mouse tissues were not remarkably high (compared to heavily polluted sites), concern is warranted because: (1) Isle Royale National park is a protected area in a remote location; (2) any exposure in deer mice represents a path for biomagnification in the terrestrial food web; and (3) the source of this mercury remains unidentified.     

The causes and consequences of partial prey consumption by wolves preying on moose

For a wide range of taxa, partial prey consumption (PPC) is a frequent occurrence. PPC may arise from physiological constraints to gut capacity or digestive rate. Alternatively, PPC may represent an optimal foraging strategy. Assessments that clearly distinguish between these causes are rare and have been conducted only for invertebrate species that are ambush predators with extra-intestinal digestion (e.g., wolf spiders). We present the first strong test for the cause of PPC in a cursorial vertebrate predator with intestinal digestion: wolves (Canis lupus) feeding on moose (Alces alces). Previous theoretical assessments indicate that if PPC represents an optimal foraging strategy and is not caused by physiological limitations, then mean carcass utilization is negatively correlated with mean kill rate and the utilization of individual carcasses is uncorrelated with time between kills. Wolves exhibit exactly this pattern. We explore how the typical portrayal of PPC by wolves has been not only misleading but also detrimental to conservation by promoting negative attitudes toward wolves.     

Erosion of Heterozygosity in Fluctuating Populations

Abstract: Demographic, environmental, and genetic stochasticity threaten the persistence of isolated populations. The relative importance of these intertwining factors remains unresolved, but a common view is that random demographic and environmental events will usually drive small populations to the brink of extinction before genetic deterioration poses a serious threat. To evaluate the potential importance of genetic factors, we analyzed a model linking demographic and environmental conditions to the loss of genetic diversity in isolated populations undergoing natural levels of fluctuation. Nongenetic processes—environmental stochasticity and population demography—were modeled according to a bounded diffusion process. Genetic processes were modeled by quantifying the rate of drift according to the effective population size, which was predicted from the same parameters used to describe the nongenetic processes. We combined these models to predict the heterozygosity remaining at the time of extinction, as predicted by the nongenetic portion of the model. Our model predicts that many populations will lose most or all of their neutral genetic diversity before nongenetic random events lead to extinction. Given the abundant evidence for inbreeding depression and recent evidence for elevated extinction rates of inbred populations, our findings suggest that inbreeding may be a greater general threat to population persistence than is generally recognized. Therefore, conservation biologists should not ignore the genetic component of extinction risk when assessing species endangerment and developing recovery plans.     

Population Variability and Extinction Risk

Abstract: Population models generally predict increased extinction risk (ER) with increased population variability (  PV  ), yet some empirical tests have provided contradictory findings. We resolve this conflict by attributing negative measured relationships to a statistical artifact that arises because PV tends to be underestimated for populations with short persistence. Such populations do not go extinct quickly as a consequence of low intrinsic variability; instead, the measured variability is low because they go extinct so quickly. Consequently, any underlying positive relationship between PV and ER tends to be obscured. We conducted a series of analyses to evaluate this claim. Simulations showed that negative measured relationships are to be expected, despite an underlying positive relationship. Simulations also identified properties of data, minimizing this bias and thereby permitting meaningful analysis. Experimental data on laboratory populations of a bruchid beetle (Callosobruchus maculatus) supported the simulation results. Likewise, with an appropriate statistical approach (Cox regression on untransformed data), reanalysis of a controversial data set on British island bird populations revealed a significant positive association between PV and ER (p = 0.03). Finally, a similar analysis of time series for naturally regulated animal populations revealed a positive association between PV and quasiextinction risk (p < 0.01). Without exception, our simulation results, experimental findings, reanalysis of published data, and analysis of quasiextinction risk all contradict previous reports of negative or equivocal relationships. Valid analysis of meaningful data provides strong evidence that increased population variability leads to increased extinction risk.