Mechanisms of cohort suppression and population fluctuation in tiger salamanders

Conference (2006)

The mechanisms underlying population fluctuation have been well studied in mammals and insects but less research has focused on amphibians. Yet, the current global decline of amphibians equires that we ... [more ▼]

The mechanisms underlying population fluctuation have been well studied in mammals and insects but less research has focused on amphibians. Yet, the current global decline of amphibians equires that we understand these mechanisms, and be able to distinguish between anthropogenically induced declines and natural population fluctuations. We have followed a marked population of the Arizona tiger salamander, Ambystoma tigrinum nebulosum, for over 16 years during which time the population has completed two “boom and bust” cycles, generated by a dominant cohort that appears to suppress larval recruitment until it senesces. We tested two hypotheses for this suppression, cannibalism and resource depression, using a series of meso- and microcosm experiments. We found significant lethal and sublethal (behavior, diet, growth rates) effects of cannibalism by large larvae and paedomorphic adults on hatchling and 1st-year larvae, suggesting that both cannibalism and the threat of cannibalism are important in cohort suppression. Resource depression experiments revealed that paedomorphic adults did not affect larval survival, diet, or growth, despite reduced prey densities, because paedomorphs mainly reduced large bodied prey, whereas hatchlings fed primarily on smaller benthic and zooplanktonic invertebrates. Future experiments will determine how hatchlings are impacted by boom cohorts that are more similar in size and diet. Our results lend insight into the mechanisms underlying fluctuations in this population, and suggest that a better understanding of natural population fluctuations will aid amphibian conservation efforts. [less ▲]

Mechanisms of larval cohort suppression and population fluctuation in tiger salamanders.

Conference (2006)

The mechanisms underlying population fluctuation have been well studied in mammals and insects but less research has focused on amphibians. Yet, the current global decline of amphibians requires that we ... [more ▼]

The mechanisms underlying population fluctuation have been well studied in mammals and insects but less research has focused on amphibians. Yet, the current global decline of amphibians requires that we understand these mechanisms, and be able to distinguish between anthropogenically induced declines and natural population fluctuations. We have followed a population of the Arizona tiger salamander, Ambystoma tigrinum nebulosum, over 16 years and through two cycles of population fluctuation, which is typified by the production of “boom” cohorts followed by suppression of larval recruitment by paedomorphic adults in this cohort. We tested two hypotheses for this suppression, cannibalism and resource depression, using a series of meso- and microcosm experiments. We found significant direct (mortality) and indirect (behavior, diet, growth rates) effects of cannibalism by larger larvae and paedomorphic adults on hatchling and 1st-year larvae, suggesting that both cannibalism and the threat of cannibalism play a large role in suppression of larval cohorts. In contrast, paedomorphic adults showed no substantial effects on larval survival, diet, or growth via resource depression, in part because paedomorphic adults reduced availability of large benthic invertebrates, while hatchlings fed primarily on smaller benthos and zooplankton. However, current experiments suggest that hatchlings can be impacted by cohorts of larvae that are more similar in size and diet. Our results lend insight into the mechanisms underlying fluctuations in this population, and suggest that a better understanding of natural population fluctuations will aid amphibian conservation efforts. [less ▲]

Feeding habits in a dimorphic metapopulation of the tiger salamander Ambystoma tigrinum nebulosum

Conference (2003)

Facultative paedomorphosis in salamanders refers to the presence of two ontogenetic pathways in natural populations – paedomorphosis, in which individuals retain gills at the adult stage, and ... [more ▼]

Facultative paedomorphosis in salamanders refers to the presence of two ontogenetic pathways in natural populations – paedomorphosis, in which individuals retain gills at the adult stage, and metamorphosis, in which larvae metamorphose. The Mexican Cut Nature Preserve (Colorado, USA) is composed of numerous ponds which are inhabited by paedomorphic and metamorphic tiger salamanders. While paedomorphs usually stay in the same aquatic habitat all their life, metamorphs may leave water and colonize other ponds. The aim of this study was to determine the feeding habits of the two morphs from this metapopulation. To this end, adults were caught by dip-netting, stomach-flushed, measured and marked. Paedomorphs were only found in permanent waters. Metamorphs were present in all habitats, but particularly in the temporary ponds. Diet differed between ponds – reflecting their invertebrate composition – with a preponderance of either microcrustaceans, fairy shrimp or insect larvae. In ponds inhabited by the two morphs, paedomorphs consumed more prey items. Because dry mass and energy content varied between invertebrates, feeding on some of them, such as fairy shrimp in the temporary ponds where they are abundant, gave high energy intake to the predators. Because such resources are only available to the dispersive morph, metamorphs are at the advantage in being able to avoid competition with paedomorphs in permanent ponds and in using transient resources from the productive temporary waters. [less ▲]