Frogs in plants: Ecology and conservation of a bromeliad-dwelling amphibian from Brazil

This thesis investigates the population ecology and population dynamics of a species of bromeligenous frog, Crossodactylodes itambe, endemic to a highland area in the Atlantic Rainforest of Brazil, within the Espinhaço Mountain Range. Bromeligenous frogs spend their entire life cycle inside bromeliads and dispersal of individuals is still unknown. There are 99 species of bromeligenous frogs, all restricted to the Neotropics, and most species are threatened. Crossodactylodes is comprised of five small-sized bromeligenous frogs and there is little information on their ecology and natural history of the whole genus. Crossodactylodes itambe occurs at the Itambé summit, above 1700 m in elevation, with an estimated area of occurrence of < 0.5 km2. Individuals are known to occupy a single species of bromeliad, which is also endemic to just two localities, including the Itambé summit.

Species abundance was influenced by specific features of habitat structure, such as size of plant and presence of water, which were considered more important than local climate. Number of adults in a single plant was usually limited to one individual and the structure of the bromeliad was considered extremely important for species persistence. Distribution of plants at the Espinhaço Range was influenced by topography and specific climatic conditions, such as temperature seasonality and annual precipitation. Given the strong dependence of the frogs on the plant, using bromeliads as a surrogate for modelling frog distribution can be extended to many bromeligenous species that lack distributional data. Despite extensive survey effort, Crossodactylodes itambe cannot be found anywhere else within the southern limits of the Espinhaço Range, and the species is indeed naturally rare.

Detecting declines in amphibian populations is challenging and surveys should be species-specific and designed to meet specific monitoring goals. A sampling design was suggested for Crossodactylodes itambe, which can detect large to moderate population changes with 80% statistical power. The first analysis of population trends for a bromeligenous frog was provided. Although population changes were detected at all elevational ranges covering the current species distribution, a decline was only significant at lower elevations, where bromeliads are smaller and occur at lower density. While colonization of bromeliads by frogs was driven by habitat characteristics, local extinction was explained by seasonal variation in local weather conditions. Colonization rates were negatively affected by a stochastic fire event, which decreased dramatically in burnt plants.

This thesis provides valuable information on the drivers of distribution and abundance of this threatened frog species. The same methodological approaches could be broadly applied to many Data Deficient bromeligenous frogs, for which little information is available. This research also demonstrates how the frog-bromeliad system can be a useful small-scale model for investigating key demographic parameters, such as extinction and colonization, which might be unfeasible on a larger scale or in patchy habitats. Considering the population dynamics of this bromeligenous frog, in the short-term, habitat conservation should be a priority action when compared to climate change mitigation.