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While organisms are typically considered permanent residents of a community, many transient organisms occupy a community for only brief periods. Despite the duration, the effects of a short visit by a top predator may remain long after departure. To test hypotheses on the impacts of a short-term visit by a top predator on pond communities, we used artificial ponds and constructed food web treatments that varied in trophic structure (Control Food Web = no predators present, Bluegill Food Web = only intermediate predators present, and Full Food Web = top and intermediate predators present). The constructed food webs were replicated five times and contained two prey species (frog tadpoles), an intermediate predator (fish), and one top predator (freshwater turtle). The Full Food Web simulated a four-day visit by Chelydra serpentina (Common Snapping Turtle). Predation by Lepomis macrochirus (Bluegill) reduced mean tadpole survival for Hyla chrysoscelis (Cope's Gray Tree Frog) in all food webs, including the Full Food Web with C. serpentina, compared to the Control Food Web. Although C. serpentina had no effects on tadpoles of H. chrysoscelis, the top predator reduced mean survival and increased mean mass of Rana sphenocephala (Southern Leopard Frog) when compared to the Bluegill Food Web. Therefore, our results suggest that brief visits from transient organisms, especially top predators, can alter community structure and initiate cascading effects.

Map turtles of the genus Graptemys are highly aquatic and rarely undergo terrestrial movements, and limited dispersal among drainages has been hypothesized to drive drainage-specific endemism and high species richness of this group in the southeastern United States. Until recently, two members of the megacephalic “pulchra clade,” Graptemys barbouri and Graptemys ernsti, were presumed to be allopatric with a gap in both species' ranges in the Choctawhatchee River drainage. In this paper, we analyzed variation in morphology (head and shell patterns) and genetics (mitochondrial DNA and microsatellite loci) from G. barbouri, G. ernsti, and Graptemys sp. collected from the Choctawhatchee River drainage, and we document the syntopic occurrence of those species and back-crossed individuals of mixed ancestry in the Choctawhatchee River drainage. Our results provide a first counter-example to the pattern of drainage-specific endemism in megacephalic Graptemys. Geologic events associated with Pliocene and Pleistoce...

Phenotypic variation within a species can be associated with genetic differentiation and varying environmental conditions among populations and their habitats. The relationship between environmenta...

We investigated the annual nesting ecology of a population of Desert Tortoises (Gopherus agassizii) inhabiting a utility-scale renewable energy (USRE) facility in southern California and compared our results with populations inhabiting relatively undisturbed sites. In 2000, 15 radio-tracked females produced 29 clutches, and 24 nests were monitored to examine nest-site selection, nest predation, hatching success, date of emergence of hatchlings, and hatchling mass and carapace length. Overall, the nesting ecology of the population inhabiting the USRE facility was very similar to other populations of Desert Tortoises inhabiting relatively undisturbed habitats. Oviposition occurred from 12 May to 8 July, which was similar to other sites. Nest depths (11.1 cm), nest predation (12%), hatchling emergence date (7 August and 29 September), and hatchling morphometrics (i.e., MCL: 44.5 mm; mass: 23 g) were all within ranges reported in other populations. Unlike within other populations, we observed no relationship ...