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Ecological dynamics & Wildlife ecology in the Anthropocene
Research lines
Ecological dynamics & Wildlife ecology in the Anthropocene
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Check below some details of my current research lines
Research: Research
Regulation of trophic interactions, community & ecosystem dynamics by large herbivores & frugivores
I am leading a research agenda that aims to provide experimental evidence on the functional role of different types of large tropical forest herbivores. Studies on iconic large African grazers and browsers are well documented, and the dynamic feedbacks between plants, herbivores and their predators in tropical savannahs and, to a lesser extent, temperate forests and grasslands have been intensively studied. Ironically, despite holding high levels of diversity and providing critical ecosystem services at the global scale, the dynamic feedbacks involving large herbivores on tropical forests are poorly understood. Unlike on grasslands and temperate forests, many large herbivores on tropical forests are frugivores, relying on fruits as a key food resource. In turn, many trees in tropical forests produce fruits that sustain and are dispersed by animals. Consequently, plant-herbivore feedbacks on these systems do not fit well within the general frameworks developed for other ecosystems. Frugivory adds a totally new dimension to the kind of dynamics observed on classical plant-herbivore systems, where antagonisms, and not mutualisms such as assisted seed dispersal, are thought to play a critical role.
I have recently introduced the concept of "FRUITING LAWNS", a positive feedback process between fruit production, consumption & disturbance by large frugivores, and soil nutrient cycling. This work is currently focused on the Atlantic Forest of Brazil, where we run a long-term multi-site experimental defaunation study aiming to disentangle the regulatory role of the two most dominant species in most of the neotropics -the lowland tapir (a generalist frugivore and browser) and the white-lipped-peccary (a generalist frugivore and omnivore)- on community dynamics and ecosystem functions. During my FAPESP postdoctoral Fellowship in Brazil, I have demonstrated that white-lipped-peccary strongly limits plant recruitment, and that these large ground-dwelling tropical forest herbivores increase beta diversity in regenerating seedling communities, but only when they occur simultaneously. This might be the result of complementary mutualistic dispersal & antagonistic disturbance functions, but this meta-community style model is still highly speculatory. I am currently assessing how these large herbivores affect nitrogen cycling and primary productivity at the understory, and collaborating in disentangling their impact on plant functional and phylogenetic diversity, soil microbial communities, plant biomass allocation strategies and fitness, and, more generally, above-belowground feedbacks.
During my PhD on the upland grasslands of Scotland, I experimentally studied how livestock grazing effects on rodent densities and dynamics affects other trophic levels directly and indirectly linked to rodent fluctuations in temperate grasslands (predators, insectivores, invertebrates and plants). Our work suggests that moderate grazing intensities is a feasible solution in order to minimize impacts of livestock grazing on wild communities.
Research: Research
Coexistence, assembly and adaptation to the Anthropocene
I am very interested in studying if and how communities can cope with the Anthropocene, and if and how populations might achieve this by altering their behavior, interactions and life-history strategies, or ultimately, through rapid evolutionary change. Classical studies suggest that niche partitioning seems to resolves competitive exclusion fairly well. However, when humans mess around with populations, alter community structure and disrupt ecosystem functions, the spectrum of available niches changes, and coexistence and equilibrium dynamics might become a hard business.
I have recently started to investigate empirically patterns of coexistence in human altered ecosystems. The work of my former MRes student P. Akkawi, demonstrated a dominance hierarchy in palm resource partitioning amongst mammalian frugivores (white-lipped-peccary, collared peccary and agouti) in a highly isolated forest fragment of the Atlantic Forest of Brazil. Palms are a key resource in this tropical forest ecosystem, and dominance hierarchies in resource exploitation can promote coexistence. Our results suggest that coexisting species can cope with isolation and high resource overlap by exploiting different resources with different intensity. Yet, ongoing work with Brazilian collaborators using isotopes suggests strong dietary shifts towards animal prey in large frugivores inhabiting fragmented forests.
Defaunation is another ubiquitous phenomenon across the world´s ecosystems. Making use of our long-term multisite large frugivore exclusion experiment in the Atlantic Forest of Brazil, me and my former MRes student P. Akkawi are deciphering whether large frugivores competitively exclude small mammals from tropical forests (these thrive in the absence of the former, a phenomenon known as “rodentation”). In addition, with Yuri Souza, a MRes student, I am inspecting how the coexistence between different plant life-forms is altered by the extinction of large frugivores. Furthermore, I have previously found that large frugivores decrease and stabilize the dominance of abundant plant species in tropical forests, favoring subdominant ones (but not rare species), and increasing community (beta) diversity. I am currently starting to investigate whether this might be due to altered metacommunity dynamics.
Research: Research
Population regulation and demography under pressure
I am fascinated by the phenomenon of density dependence and how this might be affected by human pressures. All biological processes are regulated, and the dynamics of populations and communities are no exception. Natural ecosystems are clearly structured and elegantly organized in populations that play different functions and that show relatively stable trajectories. I am interested in disentangling the relative importance of different processes in regulating demography and population sizes of different functional types of organisms, and understanding how anthropogenic pressures mess up with these.
In my PhD, I demonstrated experimentally that intense livestock grazing suppresses field vole (Microtus agrestis) population cycles on upland grasslands of Scotland. One hypothesis is that through reduced vegetation shelter and/or food available for small mammals, livestock grazing might lead to higher predation (increased top-down regulation) or starvation (competitive exclusion). Our results rejected both hypotheses. We demonstrated that generalist predation declined concomitantly to small mammal densities, and that delayed density dependence (commonly attributed to numerical changes in specialist predation) decreased with livestock grazing. Using capture-mark-recapture in the same experimental set up, I also showed that livestock grazing affected recruitment but not survival during the low, increase and peak phases of the small mammal cycle, suggesting that neither predation nor starvation nor parasitism were responsible for such declines. Hence, livestock must be messing around with a more elusive mechanism (availability of nesting sites, changes in social dynamics).
I also collaborated in an experimental test of the synergic effects of predation and disease in the crash of the European rabbit (Oryctolagus cuniculus) populations in my beloved Iberian Peninsula, where these have been declining since the introduction of myxomatosis in the 80´s. We demonstrated that predation affects rabbit survival, so that management aiming to improve cover would benefit rabbit populations, but that the benefits of a vaccination campaign were very narrow.
Research: Research
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