Seminatrix pygaea, a model of ecological resilience in dynamic habitats
Winne, Christopher T.
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To capitalize on productive wetland habitats, organisms must cope with temporal variability in habitat suitability. Stochastic climatic variation causes variation in resource abundance, and extensive droughts can render isolated wetland habitats dry and devoid of aquatic prey for years. This dissertation documents strategies of Seminatrix pygaea, a freshwater aquatic snake, for long-term persistence in isolated wetlands. Seminatrix pygaea survived drought by aestivating within a dried wetland, unlike many sympatric snake species, which leave wetlands during drought. The first wet season following drought, S. pygaea reproduced with similar frequency and fecundity compared to pre-drought years, suggesting reproduction was unaffected by prior aestivation. The ability to rebound rapidly from drought was due partly to S. pygaea’s reproductive ecology, which was distinct from snakes exhibiting capital breeding and "adaptive anorexia". Seminatrix pygaea fed throughout pregnancy, rapidly translating high prey abundance into reproductive output through income breeding. Experiments using artificially enriched N stable isotopes as biological tracers confirmed pregnant S. pygaea can incorporate income energy into maternal and offspring body tissues during pregnancy, and revealed substantial variation in reproductive allocation strategies among individual S. pygaea. Another experiment demonstrated that reproductive costs to locomotor performance differed between aquatic and terrestrial habitats, elucidating possible reasons why aquatic habitats may enable aquatic snakes to continue foraging during pregnancy. The lack of aquatic prey during severe drought imposed significant survivorship pressures on S. pygaea, and the largest individuals, particularly females, were most adversely affected by resource limitation. Compared to pre-drought years, the largest S. pygaea were absent from the population immediately following drought, causing both maximum body size and sexual size dimorphism to be dramatically reduced. Conversely, strong positive correlations between maternal body size and indices of reproductive success in S. pygaea suggest females experience fecundity selection for large size during non-drought years. Following drought, S. pygaea quickly grow to pre-drought sizes or larger, reaching record body sizes and litter sizes within 2-4 years following wetland refilling. Overall, S. pygaea possess a distinctive suite of life-history traits enabling them to survive, reproduce, and thrive in isolated wetlands subject to periodic droughts and dramatic fluctuations in prey abundance.