SPATIAL AND TEMPORAL ECOLOGY OF OAK TOADS (BUFO QUERCICUS) ON A FLORIDA LANDSCAPE

Amphibian breeding phenology and reproductive outcome: an examination using terrestrial and aquatic sampling

Worldwide amphibian declines highlight the need for programs that monitor species presence and track population trends. We sampled larval amphibians with a box trap at 3-week intervals for 23 months in eight wetlands, and concurrently trapped adults and juveniles with drift fences, to examine spatiotemporal patterns of tadpole occurrence; explore relationships between breeding effort, tadpole abundance, and recruitment; and compare the efficacy of both methods in detecting species presence and reproductive outcome. Intermittent detection of species within and among wetlands suggested high mortality, followed by deposition of new eggs and tadpole cohorts. Breeding effort, tadpole abundance, and juvenile recruitment were generally not correlated. The reasons for this may include differential bias in detecting species or life stages between methods and high incidence of egg or tadpole mortality. Drift fences detected more species than box traps, but each provided insights regarding amphibian presence and recruitment. Our results illustrate shortfalls in the ability of infrequent aquatic sampling to detect local species richness of larval amphibians, as occurrence of many species is spatially and temporally variable. We also show the importance of using different sampling methods to detect species’ presence, as well as difficulties associated with both methods in tracking breeding effort, tadpole occurrence, or reproductive outcome.

Foraging modality and plasticity in foraging traits determine the strength of competitive interactions among carnivorous plants, spiders and toads

Foraging modalities (e.g. passive, sit-and-wait, active) and traits are plastic in some species, but the extent to which this plasticity affects interspecific competition remains unclear. Using a long-term laboratory mesocosm experiment, we quantified competition strength and the plasticity of foraging traits in a guild of generalist predators of arthropods with a range of foraging modalities. Each mesocosm contained eight passively foraging pink sundews, and we employed an experimental design where treatments were the presence or absence of a sit-and-wait foraging spider and actively foraging toad crossed with five levels of prey abundance. We hypothesized that actively foraging toads would outcompete the other species at low prey abundance, but that spiders and sundews would exhibit plasticity in foraging traits to compensate for strong competition when prey were limited. Results generally supported our hypotheses. Toads had a greater effect on sundews at low prey abundances, and toad presence caused spiders to locate webs higher above the ground. Additionally, the closer large spider webs were to the ground, the greater the trichome densities produced by sundews. Also, spider webs were larger with than without toads and as sundew numbers increased, and these effects were more prominent as resources became limited. Finally, spiders negatively affected toad growth only at low prey abundance. These findings highlight the long-term importance of foraging modality and plasticity of foraging traits in determining the strength of competition within and across taxonomic kingdoms. Future research should assess whether plasticity in foraging traits helps to maintain coexistence within this guild and whether foraging modality can be used as a trait to reliably predict the strength of competitive interactions.

Ontogenetic and interspecific variation in timing of movement and responses to climatic factors during migrations by pond-breeding amphibians

Pond-breeding amphibians from temperate regions undertake overland migrations to reproduce in aquatic habitats. In turn, their offspring metamorphose and emigrate to upland, terrestrial habitats. We examined the diel patterns and daily variability of migrations of adult and juvenile amphibians in response to climatic cues. Of the eight species ( Ambystoma talpoideum (Holbrook, 1838), Ambystoma tigrinum (Green, 1825), Bufo terrestris (Bonnaterre, 1789), Hyla gratiosa LeConte, 1856, Pseudacris crucifer (Wied-Neuwid, 1838), Pseudacris ornata (Holbrook, 1836), Rana sphenocephala Cope, 1886, and Scaphiopus holbrookii (Harlan, 1935)) that we observed, all migrated almost exclusively at night except for the recently metamorphosed B. terrestris, which frequently migrated diurnally (>50% of captures). Additionally, we correlated daily captures of adult and juvenile A. talpoideum, A. tigrinum, B. terrestris, and R. sphenocephala to maximum and minimum daily temperatures, number of previous days without rain, total rainfall during the previous 24 h, and interactions of these variables. Rain was often the most important predictor of amphibian movements. However, species differed in their response to climatic factors, with some species and age classes being more dependent on rain for migrations than others. Rapid changes in regional weather patterns may affect species’ migrations differently, possibly altering arrival times of reproductive adults or affecting the likelihood of successful migrations.