Geographical gradients in diet affect population dynamics of Canada lynx

Geographical gradients in the stability of cyclic populations of herbivores and their predators may relate to the degree of specialization of predators. However, such changes are usually associated with transition from specialist to generalist predator species, rather than from geographical variation in dietary breadth of specialist predators. Canada lynx (Lynx canadensis) and snowshoe hare (Lepus americanus) populations undergo cyclic. fluctuations in northern parts of their range, but cycles are either greatly attenuated or lost altogether in the southern boreal forest where prey diversity is higher. We tested the influence of prey specialization on population cycles by measuring the stable carbon and nitrogen isotope ratios in lynx and their prey, estimating the contribution of hares to lynx diet across their range, and correlating this degree of specialization to the strength of their population cycles. Hares dominated the lynx diet across their range, but specialization on hares decreased in southern and western populations. The degree of specialization correlated with cyclic signal strength indicated by spectral analysis of lynx harvest data, but overall variability of lynx harvest (the standard deviation of natural-log-transformed harvest numbers) did not change significantly with dietary specialization. Thus, as alternative prey became more important in the lynx diet, the fluctuations became decoupled from a regular cycle but did not become less variable. Our results support the hypothesis that alternative prey decrease population cycle regularity but emphasize that such changes may be driven by dietary shifts among dominant specialist predators rather than exclusively through changes in the predator community

Managing hybridization of a recovering endangered species: The red wolf \u3ci\u3eCanis rufus\u3c/i\u3e as a case study

Hybridization presents a unique challenge for conservation biologists and managers. While hybridization is an important evolutionary process, hybridization is also a threat formany native species. The endangered species recovery effort for the red wolf Canis rufus is a classic system for understanding and addressing the challenges of hybridization. From 1987‒1993, 63 red wolves were released from captivity in eastern North Carolina, USA, to establish a free-ranging, non-essential experimental population. By 1999, managers recognized hybridization with invasive coyotes Canis latrans was the single greatest threat to successful recovery, and an adaptive management plan was adopted with innovative approaches for managing the threat of hybridization. Here we review the application and results of the adaptive management efforts from 1993 to 2013 by comparing: (1) the numbers of wolves, coyotes, and hybrids captured, (2) the numbers of territorial social groups with presumed breeding capabilities, (3) the number of red wolf and hybrid litters documented each year and (4) the degree of coyote introgression into the wild red wolf gene pool. We documented substantial increases in the number of known red wolves and red wolf social groups from 1987–2004 followed by a plateau and slight decline by 2013.The number of red wolf litters exceeded hybrid litters each year and the proportion of hybrid litters per year averaged 21%. The genetic composition of the wild red wolf population is estimated to include \u3c 4% coyote ancestry from recent introgression since reintroduction. We conclude that the adaptive management plan was effective at reducing the introgression of coyote genes into the red wolf population, but population recovery of red wolves will require continuation of the current management plan, or alternative approaches, for the foreseeable future. More broadly, we discuss the lessons learned from red wolf adaptive management that could assist other endangered species recovery efforts facing the challenge of minimizing hybridizatio

Assessment Of Canada Lynx Research And Conservation Needs In The Southern Range: Another Kick At The Cat

The ecology of Canada lynx (Lynx canadensis) and their main prey, snowshoe hares (Lepus americanus), is poorly understood in southern Canada and the contiguous United States compared to the boreal forest of Canada and Alaska, USA, where both species are well studied. However, given recent listing of lynx under the Endangered Species Act, accurate understanding of lynx and snowshoe hare ecology and conservation requirements in the United States is a high priority. We critically examined unchallenged perceptions and important research needs related to lynx and hare ecology and conservation at the southern extent of their range. Contrary to popular dogma, lynx do not require old-growth forest for denning, but further research on lynx and hare use of fragmented landscapes at lower latitudes is required. The contention that southern lynx are subject to higher interference or exploitative competition compared to their northern counterparts remains without strong empirical support. Lynx rely more on red squirrels (Tamiasciurus hudsonicus) and possibly other alternate prey at lower latitudes, but hares are the predominant food type for lynx across their range. Southern lynx and hare populations do not exhibit periodic cyclicity, but harvest statistics suggest that lynx abundance in the southern range is highly variable, implying that numerical fluctuations likely are fueled by immigration from Canada. Southern lynx population viability in the absence of ingress is suspect and thus maintaining connectivity with northern areas of occupancy should be a priority. Successful conservation of lynx populations in the contiguous United States will require 1) improved understanding of lynx population and habitat ecology at lower latitudes, 2) protection and management of large tracts of lynx and snowshoe hare habitat, and 3) ensured connectivity between lynx populations at the core and periphery of the species\u27 range. However, in light of the numerous challenges facing conservation of populations of many species at their southern distributional limit, the long-term prognosis for lynx in the southern range currendy is uncertain

Spatial Dynamics Of Sympatric Canids: Modeling The Impact Of Coyotes On Red Wolf Recovery

Interspecific competition can have a substantial impact on sympatric carnivore populations and may threaten reintroduction attempts of threatened or endangered species. Coyotes (Canis latrans) are the primary threat to recovery of red wolves (C. rufus) in the wild, through hybridization and loss of the red wolf genotype and habitat occupancy that reduces space available for wolf occupation. We built a stochastic simulation model (using data collected from a recovering red wolf population in northeastern North Carolina as well as from the literature) to examine spatial dynamics of sympatric red wolves and coyotes (independent of habitat influences) and to elucidate the potential role of coyotes on wolf recovery and reintroduction success. Survival of juvenile and adult wolves had the greatest impact on wolf population size and likelihood of extinction. Introducing coyotes to the model had a substantial negative impact on wolf numbers, and the model was highly sensitive to the estimates of the competitive impact of coyotes on red wolves, through declines in wolf productivity. We simulated coyote management from either removal (lower coyote survival) or surgical sterilization (lower coyote reproductive rates) and found that both management strategies increased viability of red wolf populations, especially during initial colonization. Our results suggest that coyotes can inhibit red wolf reintroduction success through competitive interactions, but that management of coyote populations can improve the probability of successful wolf recovery. Additional information on spatial dynamics and dietary overlap between coyotes and wolves in the recovery area is needed to further elucidate the current and potential competitive impact of coyotes on red wolf populations. © 2008 Elsevier B.V. All rights reserved

Incubation temperature influences sex ratio and offspring’s body composition in Zebra Finches (Taeniopygia guttata)

Incubation temperature has the potential to influence offspring sex, phenotype, and survival, particularly in species with temperature-dependent sex determination. However, relatively little is known about how incubation temperature affects sex ratio and offspring condition in other animals. Incubating birds allocate varying time for egg incubation depending on the parents’ condition and ambient temperature, likely altering nest microclimate. To understand how incubation temperature impacts offspring phenotype in birds, we artificially incubated Zebra Finch (Taeniopygia guttata (Vieillot, 1817)) eggs at 36.2, 37.4, or 38.4 °C during the entire incubation period and examined sex ratio and offspring quality. We found that incubation temperature of 36.2 °C resulted in a greater likelihood of a young being male compared with 37.4 °C, indicating that it is more likely for males to survive until the juvenile stage compared with females in the 36.2 °C group. We also found sex-specific effects of incubation temperature on body composition. Although incubation temperature did not affect fat or lean mass of female young, male offspring from the 38.4 °C group had significantly less lean mass throughout their lives compared with males from 37.4 or 36.2 °C. This study shows that there are sex differences in the effects of incubation temperature, and variable incubation temperature has a capacity to influence offspring secondary sex ratio and body condition in songbirds

Appendix D. Summary statistics for estimates of 10 duck species surveyed annually in central North America.

Summary statistics for estimates of 10 duck species surveyed annually in central North America

Appendix E. Parameter estimates for population growth models fit to time series for 10 duck species.

Parameter estimates for population growth models fit to time series for 10 duck species

Appendix B. Results from simulations assessing statistical power in detection of density dependence.

Results from simulations assessing statistical power in detection of density dependence

Appendix F. AICc differences (Δi) and AICc weights (wi) for three growth models fit to population time series for 10 duck species.

AICc differences (Δi) and AICc weights (wi) for three growth models fit to population time series for 10 duck species

Appendix C. Population counts for 10 duck species in central North America.

Population counts for 10 duck species in central North America