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Cloyed C.S.,National Great Rivers Research and Education Center | Eason P.K.,University of Louisville
Evolutionary Ecology | Year: 2016

Individual generalist predators often have more specialized diets than their populations do. Individual specialization (IS) is influenced by ecological opportunity, intraspecific competition, and interspecific competition, although the effects of these parameters are inconsistent across studies. We investigated IS in five species of frogs and toads, Anaxyrus americanus, A. fowleri, Lithobates catesbeianus, L. clamitans, and L. sphenocephalus. We used the natural history and ecology of each species to predict which parameters would influence IS. Our predictions were supported for some species but not others. We predicted IS would be positively influenced by resource diversity in all species, but this prediction held for only three species, with the relationship significant in A. fowleri and L. catesbeianus and marginally significant in A. americanus. We also predicted that interspecific competition would have a negative relationship with IS in L. clamitans because L. catesbeianus is competitively superior to L. clamitans and likely to suppress its foraging options. This prediction was upheld. Finally, we predicted that IS in A. americanus, A. fowleri, and L. clamitans would be influenced by intraspecific competition. However, IS was not influenced by intraspecific competition in any species, a surprising result given that intraspecific competition has traditionally been assumed to be the ecological parameter with the strongest effects on IS. Many previous studies did not simultaneously consider all three ecological parameters, which may have increased the apparent importance of intraspecific competition for IS. Our results revealed that the ecological parameters affected IS differently even across closely related and ecologically similar species, and demonstrated that these differences are sometimes predictable based on natural history. This study also suggests that sympatric ecological speciation based on IS may be rare because the ecological parameters driving IS are inconsistent across species, and the strength of their effects on intraspecific diet variation varies in space. © 2016, Springer International Publishing Switzerland. Source


Peterman W.E.,Ohio State University | Crawford J.A.,National Great Rivers Research and Education Center | Hocking D.J.,U.S. Geological Survey
Copeia | Year: 2016

The size of an organism is perhaps its most overt physical characteristic, and variation in body size has long been of interest to biologists. Bergmann's rule has been actively studied and debated for more than 150 years. Despite this long history, the generality and applicability of Bergmann's rule to ectothermic organisms generally, and to plethodontid salamanders specifically, has resulted in an extensive and conflicting literature. Regardless of mechanism, clinal variation in body size has been widely observed in plethodontid salamanders and other ectothermic vertebrates. In this study, we assessed the change in adult body size of four plethodontid salamanders (Desmognathus imitator, D. ocoee, D. wrighti, and Plethodon jordani) across a 1,350 m elevational gradient in Great Smoky Mountains National Park. Using 1,293 observations of salamanders at 25 sites, we found clear and significant patterns of increasing adult body size with elevation in all four species. Average rates of increase ranged from 1.09% to 3.98% per 100 m elevation gain. We found that elevation significantly covaried with maximum and mean temperature, as well as average annual precipitation. Our study reinforces previous research describing increases in plethodontid salamander body size with elevation, but also extends these findings to fully terrestrial, direct-developing species. However, the mechanisms underlying the observed pattern are still unclear and highlight an important area for future research. As a critical life history characteristic, an understanding of geographic variation in body size is important for assessing current population dynamics, as well as the potential effects of future climate changes. © 2016 by the American Society of Ichthyologists and Herpetologists. Source


Lian Y.,University of Illinois at Urbana - Champaign | You J.-Y.,National Taiwan University | Sparks R.,National Great Rivers Research and Education Center | Demissie M.,University of Illinois at Urbana - Champaign
Journal of Hydrologic Engineering | Year: 2012

The Illinois River is a tributary of the Mississippi River that connects Lake Michigan and the Mississippi River. Starting in 1848 when the Illinois and Michigan Canal began to open, the Illinois River has experienced some major human activities such as the Lake Michigan flow diversion, creation of levee and drainage districts on floodplains, and construction of locks and dams on the river. This paper uses Pettitt-Mann-Whitney change-point statistical analysis to identify the hydrologic change points caused by human activities and to quantify hydrologic alterations in the system. Observed stage data from 12 U.S. Army Corps of Engineers gauges and observed flows from three U.S. Geological Survey gauges were used to analyze human effects on hydrologic and hydraulic conditions in the Illinois River. The year 1938 was identified as the change point for low flows and low stages and 1972 as the change point for high flows and high stages. The low flow and stage condition changes were due to a combination of added flow from Lake Michigan, levee and drainage district construction, and construction of locks and dams, whereas the high flow and stage condition changes were due to hydroclimatic change within the Illinois River basin. Analyses based on the Indicators of Hydrologic Alteration (IHA) have shown that the magnitudes, frequency, duration, and number of reversals during low flood conditions were greatly modified by: (1) the construction of locks and dams on the Illinois River that were completed in 1938, (2) the reduction of flow diversion from Lake Michigan, and (3) the hydroclimatic condition change around 1972. The latter change probably contributed to the loss of both soil-moist plants and submerged aquatic plants that once provided several important ecosystem services in the system. The analyses described in this paper, coupled with hydraulic and ecological models, can help with site selection and management plans for the ecosystem restoration of floodplains in regulated rivers. © 2012 American Society of Civil Engineers. Source


Dell A.I.,National Great Rivers Research and Education Center | Zhao L.,North China Electrical Power University | Zhao L.,Imperial College London | Brose U.,University of Gottingen | And 2 more authors.
Advances in Ecological Research | Year: 2015

We monitored the invertebrate community of leaf litter in and around a drying intermittent pool bed to explore patterns of ecological organisation across a complex environmental gradient, with particular focus on population and community size structure. We measured the body size of 24,609 individuals from 313 taxa ranging over 6 orders of magnitude in size to explore how the functional properties of individuals, populations and communities are affected by moisture (aquatic vs. terrestrial) and light (diurnal vs. nocturnal), and how these properties change across the aquatic-terrestrial habitat transition that occurs as the pool bed dried. We found strong effects of moisture on some population (size structure) and many community (species richness, abundance, evenness, biomass and size structure) properties, with additional temporal effects across the aquatic-terrestrial ecotone. There was no difference between diurnal and nocturnal populations or communities. Our results facilitate understanding of how the physical environment influences functional attributes, and particularly the size structure, of natural populations and communities. © 2015 Elsevier Ltd. Source


Garcia T.,University of Illinois at Urbana - Champaign | Jackson P.R.,U.S. Geological Survey | Murphy E.A.,U.S. Geological Survey | Valocchi A.J.,University of Illinois at Urbana - Champaign | And 2 more authors.
Ecological Modelling | Year: 2013

Asian carp are migrating towards the Great Lakes and are threatening to invade this ecosystem, hence there is an immediate need to control their population. The transport of Asian carp eggs in potential spawning rivers is an important factor in its life history and recruitment success. An understanding of the transport, development, and fate of Asian carp eggs has the potential to create prevention, management, and control strategies before the eggs hatch and develop the ability to swim. However, there is not a clear understanding of the hydrodynamic conditions at which the eggs are transported and kept in suspension. This knowledge is imperative because of the current assumption that suspension is required for the eggs to survive. Herein, FluEgg (Fluvial Egg Drift Simulator), a three-dimensional Lagrangian model capable of evaluating the influence of flow velocity, shear dispersion and turbulent diffusion on the transport and dispersal patterns of Asian carp eggs is presented. The model's variables include not only biological behavior (growth rate, density changes) but also the physical characteristics of the flow field, such as mean velocities and eddy diffusivities. The performance of the FluEgg model was evaluated using observed data from published flume experiments conducted in China with water-hardened Asian carp eggs as subjects. FluEgg simulations show a good agreement with the experimental data. The model was also run with observed data from the Sandusky River in Ohio to provide a real-world demonstration case. This research will support the identification of critical hydrodynamic conditions (e.g., flow velocity, depth, and shear velocity) to maintain eggs in suspension, assist in the evaluation of suitable spawning rivers for Asian carp populations and facilitate the development of prevention, control and management strategies for Asian carp species in rivers and water bodies. © 2013 Elsevier B.V. Source

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