Mammals are one of the most important groups in the functioning of ecosystems, and represent one of the groups under greater threat from global change and human pressures in general. Considering that nearly 25% of mammals are threatened on a global scale, the loss of their populations and consequent loss of functions can potentially represent a major threat to global scale ecosystem´s functioning and for goods and services provision. Different approaches to evaluate species diversity have been used at different scales, with species richness historically the main measure used for understanding macroecological processes or as a tool for conservation planning and prioritization. Recent developments however have addressed different dimensions of diversity, mainly from the functional and evolutionary perspective.
Functional diversity is a measure of the diversity of functions that species play within a community, and thus have implications for the functioning and resilience of ecosystems. Originally developed for plants, until recent years this measure had not been widely assessed in animals, especially mammals, and its related patterns, processes, and determinants had not yet been addressed. The aim of this thesis was to evaluate patterns of functional diversity at different scales, the effect of spatial and biogeographical scale, its spatial variation and main determinants at global, regional and national levels, as well as its relationship with human intervention and endangered species.
Mammals´ functional diversity, measured from the concept of functional richness, was evaluated by assessing patterns at three levels: globally from biogeographic regions, biomes and ecoregions, at regional level for the Neotropics and the Isthmus of Panama-Choco continuum, and at national levels in Colombia and Costa Rica. We obtained the range distribution for all mammal species from the IUCN Red List of Threatened Species and built a database of functional attributes for each species by addressing those more related with resource use and therefore exerting greater influence on ecosystem´s functioning. We estimated a functional diversity measure based on Petchey and Gaston index for each scale based on different sampling units. For global patterns we assessed functional diversity global gradients, spatial variation and its relation to the ecological and area scales across the world´s ecoregions; further we assessed the influence of threatened species on functional diversity identifying the most susceptible ecoregions to functional loss and its spatial variation. At regional scale we assessed the distribution of functional diversity for the Neotropics and the influence of human intervention and species at risk on this scale; likewise we evaluated the variation of ecological attributes for the Panama-Chocó continuum identifying gradient areas in the connection of Central and South America. For the national scale, we evaluated the distribution of functional diversity and its major biological, environmental and anthropogenic determinants for Costa Rica; furthermore, we tested the surrogacy and mismatch of functional, taxonomic and phylogenetic diversity in Colombia to assess whether the use of a single measure could represent the other as a basis for prioritizing and planning conservation actions.
We found that mammal functional diversity varies globally with clear patterns similar to species diversity, but influenced by ecological scale, species richness and geographic area in the world´s ecoregions; in turn, we determined that species richness and functional diversity do not match at global scale, so that for certain ecoregions there are underlying processes that must be considered, while a single measurement is not enough for conservation planning. Additionally, we found that threatened species are strong influencers of functional diversity at ecoregional resolution, explaining 60% of this diversity on a global scale, and varying spatially with ecoregions influenced in more than 70% of their functional diversity by threatened species. Regionally, we found that human intervention and species at risk are the main determinants of current functional diversity, where certain ecoregions have already suffered from drastic functional loss and others are more likely to suffer this loss from vulnerable species extinction. In terms of the functional attributes variation we found strong variation between Central and South America, where the convergence of functional attributes generates continuous gradients, while identifying where abrupt changes occur in assemblages´ functional composition. Nationally, we determined that functional diversity differs from the species richness gradient and is strongly influenced by the composition (i.e., bats and rodents), identifying three functionally distinct regions for Costa Rica, and that environmental, biogeographic and anthropogenic determinants influence varying depending on the region. Furthermore, we found that the three measures (i.e., functional, phylogenetic and taxonomic) vary spatially in Colombia, indicating spatial mismatch between them, also highlighting the need to select priority areas considering these three dimensions and thus ensuring the preservation of evolutionary history, ecosystems´ functioning and species diversity nationally.
Overall, functional diversity is a recent measure that advances not only in the ecological understanding of diversity but also allows to do conservation planning considering the species-ecosystem relationship, thus with implications for ecosystems functioning and resilience. Global variation and convergence can be the response to environmental filtering as well as an extraordinary trait convergence in assembling communities associated with ecosystem type and ecological regions. The results of the analyses at multiple scales allow highlighting the variation that exists in this measure of diversity, and the need to understand the patterns at different ecological and planning scales. In terms of conservation, the results have implications for the prioritization and planning of critical conservation areas, the differential impact of human intervention and the need to explore the spatial variation of the species-ecosystem relationship and its key drivers. Functional diversity should be a measure considered in future conservation schemes and its understanding will allow better resolution for exploring ecological patterns and how to support decision-making for biodiversity management and conservation.
