General Statement
I am a population biologist especially interested in the conservation biology and evolutionary ecology of endemic species. My research addresses how, why and when some species are successful (or not) in particular unique environments that have high levels of endemism by comparing demography of endemics to close relatives that are widespread. I use a variety of field, laboratory, statistical and modeling approaches to determine which biotic and abiotic factors are key to the success of individuals at different points in their life cycle and how factors acting at different phases in the life cycle affect overall success. I am interested in applications to management of endangered species.
Species of particular focus for my dissertation work was the endemic Florida leafwing butterfly, Anaea troglodyta floridalis (Nymphalidae), and its widespread congener the tropical leafwing, Anaea aidea, that occurs from Texas to Costa Rica. Leafwing butterflies have a complex life cycle that is characterized by there being multiple generations within a year, distinct seasonal forms of adults, and relatively long-lived adults who feed on nitrogen-rich sources. During a single year, the stage structure of the population changes seasonally as do the probabilities of survival and metamorphosis and the amount of reproduction. In this life cycle, the timing of allocation to different functions is likely an adaptation to historical climate (within season) and disturbance (between seasons) patterns.
Issues, questions addressed
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How vulnerable are endemic species to extinction, and how sensitive is extinction risk to natural disturbance?
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What are the survival and development rates of immature insects and how do their dynamics affect population dynamics?
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If the fates of individuals depend on life stage and season, then how do life stage changes in each season contribute to population dynamics evaluated over the entire seasonal cycle?
Research Projects (Click on image to see informative slide show)
Using randomly located vegetation surveys in the Long Pine Key area of the Everglades National Park, I investigated the factors correlated with the occurrence and abundance Croton cascarilla (Euphorbiaceae).
In a captive population of Anaea aidea and Anaea andria, caterpillars were fed controlled diets of one of five known host plants, and I evaluated the performance of caterpillars in terms of survival to pupation, development time, pupa mass, and adult size. Insect herbivores commonly feed on multiple plants throughout their geographic range, but feed locally on only one or a few plants.
I used morphometric analyses of larval head capsules that reveal sympatric leafwing populations segregated by larval food plants.
I developed a population model for the endangered Florida leafwing from 16 years of monthly counts of adult butterflies. Using the peak butterfly density as an index of population density, I modeled the yearly change in abundance with the Ricker function, a density-dependent population model. Fire is a necessary disturbance that maintains the leafwing’s habitat, and I tested for the effects of fire on r0, the theoretical growth rate at zero density, and K, the carrying capacity.
In the field, I applied mark-recapture methods to repeatedly survey tropical leafwing caterpillars in their natural environment for one month during spring. This work estimated the stage demographics of the recruitment process as a progression of individuals from egg to pupa through all juvenile stages, which is absent from most studies of butterfly demography.
Leafwing butterflies respond to seasonal extremes with an alternation of generations, in which one generation specializes in breeding and rapid development (summer form), while another generation specializes in enduring harsh conditions (winter form). Combining demographic rates estimated for the tropical leafwing in the field with demographic rates estimated in the laboratory, I constructed a periodic stage-structured matrix model that features a trade-off between survival and reproduction.