Alexander Center for Applied Population Biology

Chicago, IL, United States

Alexander Center for Applied Population Biology

Chicago, IL, United States
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Hileman E.T.,Northern Illinois University | King R.B.,Northern Illinois University | Adamski J.M.,Seneca Park Zoo | Anton T.G.,Field Museum | And 41 more authors.
PLoS ONE | Year: 2017

Elucidating how life history traits vary geographically is important to understanding variation in population dynamics. Because many aspects of ectotherm life history are climate-dependent, geographic variation in climate is expected to have a large impact on population dynamics through effects on annual survival, body size, growth rate, age at first reproduction, size-fecundity relationship, and reproductive frequency. The Eastern Massasauga (Sistrurus catenatus) is a small, imperiled North American rattlesnake with a distribution centered on the Great Lakes region, where lake effects strongly influence local conditions. To address Eastern Massasauga life history data gaps, we compiled data from 47 study sites representing 38 counties across the range. We used multimodel inference and general linear models with geographic coordinates and annual climate normals as explanatory variables to clarify patterns of variation in life history traits. We found strong evidence for geographic variation in six of nine life history variables. Adult female snout-vent length and neonate mass increased with increasing mean annual precipitation. Litter size decreased with increasing mean temperature, and the size-fecundity relationship and growth prior to first hibernation both increased with increasing latitude. The proportion of gravid females also increased with increasing latitude, but this relationship may be the result of geographically varying detection bias. Our results provide insights into ectotherm life history variation and fill critical data gaps, which will inform Eastern Massasauga conservation efforts by improving biological realism for models of population viability and climate change. © This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.

Faust L.J.,Alexander Center for Applied Population Biology | Cress D.,Pan African Sanctuary Alliance | Farmer K.H.,Pan African Sanctuary Alliance | Farmer K.H.,University of Stirling | And 2 more authors.
International Journal of Primatology | Year: 2011

Wildlife sanctuaries rescue, rehabilitate, reintroduce, and provide life-long care for orphaned and injured animals. Understanding a sanctuary's patterns in arrival, mortality, and projected changes in population size can help managers plan carefully for future needs, as well as illuminate patterns in source populations of wildlife. We studied these dynamics for chimpanzees (Pan troglodytes) in 11 sanctuaries of the Pan African Sanctuary Alliance (PASA). We analyzed historic demographic patterns and projected future population dynamics using an individual-based demographic model. From 2000 to 2006, the population in these sanctuaries has been growing at a rate of 15% per year. This growth is driven by arrivals of new individuals, with an average of 56 arrivals per year. The median age of the 760 chimpanzees living in these sanctuaries as of 2007 was 9 yr, with 76% of the population <15 yr. We found no significant difference in survivorship to age 20 between these chimpanzees and those maintained in North American accredited zoos. The size of the population in 20 yr is projected to be between 550 and 1800, depending on different assumptions about arrival and reintroduction rates. Projected shifts in age structure, including increases in the proportions of adolescent (9-19 yr of age) and older (35+) chimpanzees, may necessitate adjustments to management, veterinary care, and housing. This research illustrates how data on historic population dynamics can be modeled to inform future sanctuary capacity and management needs, allowing sanctuaries to plan better for their populations' long-term care. © 2011 Springer Science+Business Media, LLC.

Foley C.A.H.,Wildlife Conservation Society | Faust L.J.,Alexander Center for Applied Population Biology
ORYX | Year: 2010

We studied the demography of a subpopulation of African elephants Loxodonta africana in Tarangire National Park, Tanzania, from 1993 to 2005. The Tarangire elephants had been affected by heavy poaching prior to 1993. We monitored 668 individually known elephants in 27 family groups. The population increased from 226 to 498 individuals, with mean group size increasing from 8.4 to 18.3. The average annual growth rate was 7.1% (range 2.0-16.9%). This approaches the maximal growth rate for African elephants, with corresponding minimal values for demographic parameters. The mean interbirth interval was 3.3 years, mean age of first reproduction 11.1 years, average annual mortality of elephants younger than 8 years 3%, and average annual mortality of adult females 1%. Probability of conceiving was positively correlated with annual rainfall. No significant density-dependent effects were recorded. Rapid growth was aided by high rainfall, low population density and release from the stresses of poaching. These results demonstrate that elephant populations are capable of rapid population increases for extended periods of time given the right ecological and social conditions. This has consequences for elephant conservation and management. Copyright © 2010 Fauna & Flora International.

Simonis J.L.,Cornell University | Simonis J.L.,Alexander Center for Applied Population Biology
Ecosphere | Year: 2013

Ontogenetic changes in consumers can influence the magnitude and outcome of direct and indirect ecological interactions. Although most research has focused on the consequences of qualitative changes in diet (i.e., shifts in trophic guild between life-history stages), quantitative effects of ontogeny, such as size-dependent per capita consumption rates, likely also influence food webs by modulating the relative importance of top-down control. I examined the effect of predator ontogeny on per capita consumption rates, selectivity between prey species, and the resulting food-web consequences using a system of freshwater rock pools on Appledore Island, Maine, USA. The rock pools house a simple tritrophic food chain consisting of chlorophyte algae consumed by cladoceran grazers (Moina macrocopa and Daphnia pulex), which are then preyed upon by the aquatic insect Trichocorixa verticalis (Corixidae). Laboratory studies showed that Trichocorixa grows substantially during its life history, with size-dependent (i.e., allometric) increases in per capita predation rates (consuming both Moina and Daphnia). Predation rates were significantly higher on Moina than Daphnia in single-prey experiments and all instars of Trichocorixa significantly preferred Moina in choice experiments. In a mesocosm experiment, predation by Trichocorixa on zooplankters created a top-down trophic cascade by releasing phytoplankton from grazing and the strength of the cascade increased significantly with Trichocorixa life-history stage. A yearlong observational study of three rock pools in the field indicated that top-down interactions are present and strongly affect food-web dynamics in situ, as well. In particular, time-series modeling showed that increases in Trichocorixa biomass (due to ontogenetic growth and hatching) led to decreases in Moina population growth rates, which caused increases in phytoplankton population growth rates. Taken together, these results indicate that consumer ontogeny can affect food-web and ecosystem dynamics without qualitative niche shifts if per capita feeding rates change substantially over the consumer's life history. Given the prevalence of both allometrically scaling consumption rates and dynamically structured predator populations, top-predator demography may be an important driver of the trophic structure and dynamics of food webs. Copyright: © 2013 Simonis.

Pellowe-Wagstaff K.E.,Cornell University | Simonis J.L.,Cornell University | Simonis J.L.,Alexander Center for Applied Population Biology
Freshwater Biology | Year: 2014

Summary: The dispersal of organisms in fragmented habitats connects spatially separated local populations at the regional, metapopulation scale, with potential consequences for spatial population dynamics and persistence. As any dispersing organism is engaged in trophic interactions as well, dispersal also connects local food webs at the regional scale, and differential dispersal among taxa of different trophic levels has the potential to strongly influence spatial food-web dynamics. We used a combination of field surveys and experiments to test the significance of passive dispersal via overflowing water for population and food-web dynamics in a system of freshwater rock pools on Appledore Island, Maine, U.S.A. The rock pools contain a three-trophic-level food chain consisting of phytoplankton (primarily chlorophyte algae), grazer zooplankton (two species of Cladocera) and a predatory insect (Trichocorixa), all of which are passively dispersed between rock pools when the pools overflow during rain events. During the summers of 2010 and 2011, rain events were observed (on average) every two and a half days. Three-quarters of rain events generated overflows, and observed overflow rates varied over four orders of magnitude (0.5-474 mL s-1). A Monte Carlo simulation showed that, on average, a pool is expected to overflow 5.6 times during a summer. Despite all three taxa dispersing in overflows, and dispersing more at higher flow rates, a mesocosm experiment showed that dispersal rates decreased significantly with increasing trophic level, such that Trichocorixa dispersed less than cladocerans, which dispersed less than phytoplankton. Results from a follow-up experiment suggest that this decrease in dispersal is primarily due to organisms at higher trophic levels being more able to avoid currents, rather than an ability to swim more strongly against currents. Finally, we conducted a field experiment to determine the influence of overflows on population and food-web dynamics in situ. Populations in pools that were part of experimental overflows were significantly more variable than nearby populations that were not in the overflow, and taxa at all three trophic levels were influenced similarly by the overflows. This study demonstrates that passive dispersal of aquatic organisms among habitat patches is likely to occur at different rates for different taxa, which may have strong effects on spatial food-web dynamics. © 2014 John Wiley & Sons Ltd.

Simonis J.L.,Cornell University | Simonis J.L.,Alexander Center for Applied Population Biology | Ellis J.C.,Tufts University
Ecology | Year: 2014

Metacommunity theory generally predicts that regional dispersal of organisms among local habitat patches should influence spatial patterns of species diversity. In particular, increased dispersal rates are generally expected to increase local (α) diversity, yet homogenize local communities across the region (decreasing β-diversity), resulting in no change in regional (γ) diversity. Although the effect of dispersal on a-diversity has garnered much experimental attention, the influence of dispersal rates on diversity at larger spatial scales (β and γ) is poorly understood. Furthermore, these theoretical predictions are not well tested in the field, where other environmental factors (e.g., habitat size, resource density) likely also influence species diversity. Here, we used a system of freshwater rock pools on Appledore Island, Maine, USA, to test the effects of dispersal rate on species diversity in metacommunities. The pools exist in clusters (metacommunities) that experience different levels of dispersal imposed by gulls (Larus spp.), which we show to be frequent passive dispersers of rock-pool invertebrates. Although previous research has suggested that waterbirds may disperse aquatic invertebrates, our study is the first to quantify the rate at which such dispersal occurs and determine its effects on species diversity. In accordance with theory, we found that metacommunities experiencing higher dispersal rates had significantly more homogeneous local communities (reduced β-diversity) and that γ-diversity was not influenced by dispersal rate. Contrary to theoretical predictions, however, α-diversity in the rock pools was not significantly influenced by dispersal. Rather, local diversity was significantly positively related to local habitat size, and both α- and γ-diversity were influenced by the physicochemical environment of the pools. These results provide an important field test of metacommunity theory, highlighting how local and regional factors interact to drive patterns of species diversity in metacommunities, and demonstrate that waterbirds are indeed important dispersal vectors for aquatic invertebrates. © 2014 by the Ecological Society of America.

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