Niche restriction and conservatism in a neotropical psittacine: the case of the Puerto Rican parrot
The factors which govern species‘ distribution and abundance are myriad, and together constitute the ecological niche of a given species. Because abiotic factors are arguably the most profound of the factors influencing niche boundaries and thus, species distributions, substantial changes in either climatic or habitat-related parameters can be expected to produce interrelated and profound niche shifts. Habitat loss and degradation can also effectively induce a de facto climate change by forcing populations to relocate to environmentally suboptimal habitats. Populations experiencing niche shifts due to range restrictions and geographic isolation become subject to a suite of factors that may act synergistically to amplify deleterious ecological effects of habitat loss. These factors tend to exert a greater influence on populations of rare or endemic species with inherently restricted ranges. The Puerto Rican parrot (Amazona vittata) is an example of a tropical, insular, endemic and critically-endangered species that has suffered from extensive habitat loss and degradation over the past century, resulting in a single relict wild population restricted for more than 70 years to the montane rainforest of the Luquillo Mountains in northeastern Puerto Rico. In this chapter, we examine the current ecological situation of this geographically and demographically isolated parrot population by reviewing the history of landscape-level changes in and around the Luquillo Mountains, and concurrent biotic and abiotic limiting factors in relation to both historical population trajectory and current prognosis for species recovery. We used a decade (2000-2009) of empirical data on parrot fledgling survival together with long-term climatological data to model effects of local climate on fledgling survival and gain insights into its influence on population growth. We also modeled hypothetical survival of parrot fledglings in the lowlands surrounding the Luquillo Mountains, areas currently deforested but previously occupied by parrots, to illustrate both quantitative and qualitative losses of reproductive habitat for the species. We illustrate and systematically discuss how progressive and sustained changes in landscape composition and associated limiting factors have effectively shifted and restricted the ecological niche of this species, and how this complex suite of ecological processes affects the Puerto Rican parrot in the Luquillo Mountains. Our niche restriction hypothesis is supported by the demographic response of Puerto Rican parrots recently (2006-2009) reintroduced in the lower elevation karst forest of northwestern Puerto Rico. Based on our findings, we present conservation strategies aimed at promoting the recovery of the species both in the Luquillo Mountains and elsewhere in Puerto Rico. Finally, we address the relevance of our findings to conservation of other endangered species, particularly those threatened by both habitat loss and climate change.