Regulation of Structure in Complex Systems: Experimental Temporary Pond Communities

Abstract

Interactions among competition, predation, and disturbance in determining the abundances of four species of anurans were studied in a factorial experiment using 36 replicated experimental ponds. Hatchlings of the four species (Rana utricularia, Scaphiopus holbrooki, Bufo americanus, and Hyla chrysoscelis) were introduced at the same relative abundances at a low or a high initial density. Competition determined survival, body size at metamorphosis, and length of larval period in high-density communities, which were food-limited. The predatory salamander Notophthalmus viridescens did not alter either the total number of metamorphs or their combined biomass in the high-density communities, but the relative abundance of metamorphs was shifted as Scaphiopus holbrooki, the competitive dominant, was selectively eaten. In low-density communities, predation decreased survival and biomass production of tadpoles, often to zero, in all species. For each of the four combinations of tadpole density and presence or absence of predators, ponds were drained at three rates to simulate different drying regimes. Competition slowed growth and thus increased the risk of desiccation in high-density populations in drying ponds. Predation ameliorated the effects of competition, allowing survivors to grow rapidly enough to metamorphose before ponds dried.Survival of tadpoles to metamorphosis, body size at metamorphosis, and the timing of metamorphosis were determined in a complex way by interactions among all of the treatment effects and the life history characteristics of the four species studied. Scaphiopus was the species least sensitive to tadpole density and was the competitive dominant in ponds without newts. It has a rapid growth rate and metamorphosed soon enough to escape desiccation. It suffered the greatest risk of predation and was eliminated from even some of the high-density communities. Rana was most successful in low-density communities without predators. No Rana survived in rapidly drying (50-d) ponds because of insufficient time to obtain a minimum size for metamorphosis. Rana were also eliminated from most populations exposed to predation. The effect of competition on Bufo in high-density populations, few or no survivors, was reversed by predation as newts selectively fed on Scaphiopus and Rana. This result was most striking in the tanks that dried most rapidly. Hyla did very poorly in all slowly drying ( 1 00-d) tanks compared with controls because of intense competition. It had moderate success in high-density communities where newts had removed most competitors.These results show that biological and environmental factors interact to determine the structure of anuran communities. Neither competition nor predation is the single unifying force, but rather they interact to determine the different consequences of the date of drying of a pond to the success of each species.

Gastropod communities in alpine grasslands are characterized by high beta diversity

“…Patterns of species co-occurrence might differ between disturbed and undisturbed communities (Wilbur 1987). Although several surveys suggest that invasive species can disassemble the native community structure Armett 2000, Sanders et al 2003), there is only sporadic information on how environmental gradients structure species co-occurrence patterns (Ulrich et al 2010).…”

Diet of four annual killifishes: an intra and interspecific comparison

“…This fact reinforces temporal limitations, and so, this cost should surpass costs related to competition or predation (Houston and McNamara, 1999). These strategies could maintain killifishes diversity, despite of the occurrence of four generalist vertebrate predators in a small, time constrained ecosystem (Wilbur, 1987).…”

“…Biological and environmental factors interact to determine the structure of the temporary pond communities (Wilbur, 1987). Mortality risk can be high in these habitats due to desiccation and predation by odonates, beetles and hemipterans (Wilbur, 1987).…”

“…Biological and environmental factors interact to determine the structure of the temporary pond communities (Wilbur, 1987). Mortality risk can be high in these habitats due to desiccation and predation by odonates, beetles and hemipterans (Wilbur, 1987). Animals found in that habitatsmostly macroinvertebrate and amphibian larvae-show adaptations to deal with that particular hydrological regime, such as rapid colonization and growth rate, high phenotypic plasticity (Wilbur, 1987;Marcus & Weeks, 1997;Relyea & Werner, 2000;Mura et al, 2003) or the presence of a resistance phase in their life cycle (e.g.…”

Temperature, genetic and hydroperiod effects on metamorphosis of brown frogs Rana arvalis and R. temporaria in the field

“…However, there is little (Newman, 1989) information on whether this happens in nature. Also, competition can have dramatic in¯uences on tadpole development rate and metamorph size in laboratory studies (Wilbur, 1987). Is this an important phenomenon in natural ponds?…”