Geographic Variation in Asymmetric Competition: A Case Study with Two Larval Anuran Species

Abstract

Abstract. The outcome of interspecific competition may be modulated by a large number of factors, both biotic and abiotic. In this paper, we examined experimentally the effects of geographic variation, population density, and abiotic stress on the outcome of interspecific competition between two species of larval anurans. Three different populations of natterjack toad (Bufo calamita) were set to compete with common toad (Bufo bufo) in replicated artificial ponds under different combinations of osmotic stress (freshwater or brackish water) and intraspecific density (high and low). Among the B. calamita populations used, only one of them is sympatric to B. bufo and inhabits a freshwater environment. The two other populations, allopatric to B. bufo, occupy freshwater and brackish water environments, respectively. Survival, length of the larval period, and size at metamorphosis were analyzed at both the specific and the populational interaction levels. Intra-and interspecific competition did occur and generally resulted in a decrease in survival rates, an increase in the duration of the larval period, and a decrease in size at metamorphosis. Water salinity also prolonged the larval period and interacted with intra-and interspecific density, intensifying its effects. Interspecific competition was asymmetric, since B. bufo was competitively superior to B. calamita, causing larger effects on B. calamita than those experienced by B. bufo. However, the three populations of B. calamita showed different competitive effects and responses when they were set to compete with B. bufo. The population sympatric to B. bufo had the stronger competitive effect and response, causing a strong impact on survival, growth, and developmental rate of B. bufo. The allopatric population inhabiting the brackish environment also had a marked effect on B. bufo survival, although only at high density. The other allopatric population only had a significant effect on the size at metamorphosis of B. bufo. The impact of B. bufo on B. calamita was greater for the allopatric populations than for the sympatric one. This pattern suggests that the nature and outcome of ecological interactions are a function of environmental conditions and population history.

Hierarchical competition in pond-breeding anuran larvae in a Mediterranean area

“…Our findings on competition are consistent with previous studies that have demonstrated strong asymmetric interspecific effects on the fitness-related parameters of tadpoles (e.g., Heusser, 1972aHeusser, , 1972bSmith-Gill and Gill, 1978;Wilbur, 1982Wilbur, , 1987Morin and Johnson, 1988;Griffiths, 1991;Griffiths et al, 1991;Werner, 1992;Semlitsch, 1993;Kupferberg, 1997;Parris and Semlitsch, 1998;Bardsley and Beebee, 2000;Gurevich et al, 2000;Relyea, 2000;Dayton and Fitzgerald, 2001;Gómez-Mestre and Tejedo, 2002;Smith et al, 2004;Smith, 2005). Our results, however, showed a pattern different from that detected in previous studies of desert anuran communities, in which active ephemeral pool species have a competitive advantage over less active species from temporary or permanent ponds (Woodward, 1982;Dayton and Fitzgerald, 2001).…”

Reliable effective number of breeders/adult census size ratios in seasonal‐breeding species: Opportunity for integrative demographic inferences based on capture–mark–recapture data and multilocus genotypes

“…These results were independent of the use of any sibship size prior, thus supporting the reliability of mating system inferences. Epidalea calamita lays clutches in ephemeral puddles (therefore reducing interspecific but increasing intraspecific competition), taking advantage of their fast larval development (Gómez-Mestre & Tejedo, 2002). Immediate occupancy of these ephemeral sites after heavy rainfalls is therefore critical for maximizing the opportunities for larvae to survive until metamorphosis.…”

Effects of Salinity on the Survival, Growth, Development, and Metamorphosis ofFejervarya limnocharisTadpoles Living in Brackish Water

“…Euryhaline tadpoles of Fejervarya cancrivora (formerly known as Rana cancrivora), which live in mangrove swamps experiencing wide salinity fluctuations (Alcala, 1962;Gordon and Tucker, 1965;Dunson, 1977;Uchiyama et al, 1990), can tolerate extremely high salinity (≥35 ppt) but suffer developmental retardation to the point of preventing metamorphosis (Gordon, 1961;Gordon and Tucker, 1965;Dunson, 1977;Uchiyama et al, 1990). Delayed time to metamorphosis incurs an increased risk of desiccation (Newman, 1992;Gomez-Mestre and Tejedo, 2002) and predation (Alford, 1999).…”