Ongoing research, a personal description

Ongoing Research, a description

Networks are graph representations that depict the patterns of connections among interacting elements. Mutualistic networks are assemblages of animals and plants that interact; and the outcome of the interactions has pervasive consequences for the ecology and evolution of each couterpart. Moreover, not only pairwise interactions are important in these networks: the connectedness among the different species has deep implications for the stability and persistence of the whole system.

Together with Jordi Bascompte and Jens Olesen, we are examining the topology of networks of mutualists (plant-pollinator, plant-seed disperser) in an attempt to find out invariants in the interaction patterns similar to other biotic (e.g., trophic webs), abiotic (connections among circuit components, power lines, roads among cities) or social (friendship) networks. We are comparing the patterns of connectedness and generalisation level in plant-animal mutualistic networks in the wild with those of abiotic networks and computer-simulated networks. The figure shows the patterns of interaction in a plant-frugivore community in southern Spain. Plant and bird species are arranged as separate groups of points, so that oblique blue lines connect pairs of species that interact (bird species to the left; plant species to the right). These patterns of interactions behave as broad-scale networks, showing greater stability to loss or extinction of key species compared to random networks or scale-free networks. We are investigating how these mutualistic networks buildup and what are the consequences of species extinctions, fragmentation, and overall stability for the evolution and persistence of the mutualistic interactions.

A central issue in the analysis of plant-animal coevolution is whether the patterns of mutual coadaptation can be inferred from present-day patterns of interaction. I'm using comparative methods based on the analysis of phylogenetically independent contrasts to test adaptive hypotheses about correlated evolution between fruit traits and disperser types.

Suppose that a particular difference in, say, fruit diameter or pulp lipid content has evolved in a given clade in relation to divergence in frugivore types dispersing the seeds. Then a relationship between contrasts in the fruit trait and contrasts in the proportions of frugivore types will show up when examining the patterns through a phylogeny of the group.

My previous work on this topic has concentrated on analyses for the whole Angiosperm clade. Recently I'm collaborating with Mauro Galetti and Marco Pizo, involving comparative analyses restricted to the tropical families Palmae and Myrtaceae. Together with Paulo Guimaraes, Mauro and I are also analyzing the comparative ecology of the so-called anachronic seed dispersal systems, i.e., plant species with extremely large fruits supposedly dispersed by an extinct megafauna and having present-day interactions with surrogate frugivorous animals. The dataset, and additional information, for this study is available here.

I am involved in a long term analysis of the seed dispersal system of Prunus mahaleb, a rosaceous treelet inhabiting the mountains of SE Spain. My main study area is located in the Sierra de Cazorla, Segura y las Villas, Jaén province. My main reserach focuses on the net effects of the mutualistic interaction with animal frugivores, which include birds and mammals. I am interested in the demographic, genetic, and evolutionary effects of the interaction. I started studying the system in 1980, and have continued working on it in collaboration with Eugene W. Schupp, since 1988.

My long term monitoring involves study of fruiting intensity, phenology, seed rain patterns, tree growth, and phenotypic variation in seed mass. I am studying variation in these variables for 75 trees, with data starting in 1988.

A long-standing challenge in studies of seed dispersal by animal frugivores has been the characterization of the spatial relationships between dispersed seeds and the maternal plants, i.e., the seed shadow. The difficulties to track unambiguously the origin of frugivore-dispersed seeds in natural communities has been considered an unavoidable limitation of the research field and precluded a robust analysis of the direct consequences of zoochory. Together with José A. Godoy, we are using the multilocus genotype at SSR (microsatellite) loci of the woody endocarp, a seed tissue of maternal origin, to provide an unequivocal genetic fingerprint of the source tree. By comparing the endocarp genotype against the complete set of genotypes of reproductive trees in a population, we were able to unambiguously identify the source tree for 82.1 % of the seeds collected in seed traps and hypothesized that the remaining 17.9 % of sampled seeds come from other populations. Identification of the source tree for Prunus mahaleb seeds dispersed by frugivores revealed a marked heterogeneity in the genetic composition of the seed rain in different microhabitats, with a range of 1-5 distinct maternal trees contributing seeds to a particular landscape patch. Within-population dispersal distances ranged between 0-912 m, with up to 62 % of the seeds delivered within 15 m of the source trees. We are interested in the ecological and evolutioary implications of our results, indicating strong distance limitation of seed delivery combined with infrequent long-distance dispersal events, extreme heterogeneity in the landscape pattern of genetic makeup, and a marked mosaic of multiple parentage for the seeds delivered to a particular patch. A detailed description of our field methods and lab protocols is available here.

The activity of frugivorous animals that disperse seeds has delayed consequences for plant demography. These consequences translate through the series of concatenated stages in plant recruitment that include seed delivery, survival to post-dispersal seed predators, seed germination, early seedling establishment, seedling survival up to sapling stage, and adult establishment. This is so because it matters not only how many seeds are dipsersed by frugivores, but where the seeds are delivered and which are the concatenated probabilities of survival for these seeds in particular microhabitat patches that differ in quality for recruitment after dispersal.

The figure illustrates an structural equation model fitted to the sequential probabilities of recruitment of Phillyrea latifolia in Mediterranean montane scrubland, SE Spain. The path model depicts the multiple and delayed influences, both direct and indirect, of frugivore-mediated seed-rain on later stages of recruitment.

Together with Juan-Luis García Castaño and Eugene W. Schupp, we are using this explicitly demographic approach to understand the multiple influences of frugivore activity on plant demography.

Interaction networks in plant-animal mutualisms	Networks are graph representations that depict the patterns of connections among interacting elements. Mutualistic networks are assemblages of animals and plants that interact; and the outcome of the interactions has pervasive consequences for the ecology and evolution of each couterpart. Moreover, not only pairwise interactions are important in these networks: the connectedness among the different species has deep implications for the stability and persistence of the whole system. Together with Jordi Bascompte and Jens Olesen, we are examining the topology of networks of mutualists (plant-pollinator, plant-seed disperser) in an attempt to find out invariants in the interaction patterns similar to other biotic (e.g., trophic webs), abiotic (connections among circuit components, power lines, roads among cities) or social (friendship) networks. We are comparing the patterns of connectedness and generalisation level in plant-animal mutualistic networks in the wild with those of abiotic networks and computer-simulated networks. The figure shows the patterns of interaction in a plant-frugivore community in southern Spain. Plant and bird species are arranged as separate groups of points, so that oblique blue lines connect pairs of species that interact (bird species to the left; plant species to the right). These patterns of interactions behave as broad-scale networks, showing greater stability to loss or extinction of key species compared to random networks or scale-free networks. We are investigating how these mutualistic networks buildup and what are the consequences of species extinctions, fragmentation, and overall stability for the evolution and persistence of the mutualistic interactions.
Comparative analysis of plant-animal interactions	A central issue in the analysis of plant-animal coevolution is whether the patterns of mutual coadaptation can be inferred from present-day patterns of interaction. I'm using comparative methods based on the analysis of phylogenetically independent contrasts to test adaptive hypotheses about correlated evolution between fruit traits and disperser types. Suppose that a particular difference in, say, fruit diameter or pulp lipid content has evolved in a given clade in relation to divergence in frugivore types dispersing the seeds. Then a relationship between contrasts in the fruit trait and contrasts in the proportions of frugivore types will show up when examining the patterns through a phylogeny of the group. My previous work on this topic has concentrated on analyses for the whole Angiosperm clade. Recently I'm collaborating with Mauro Galetti and Marco Pizo, involving comparative analyses restricted to the tropical families Palmae and Myrtaceae. Together with Paulo Guimaraes, Mauro and I are also analyzing the comparative ecology of the so-called anachronic seed dispersal systems, i.e., plant species with extremely large fruits supposedly dispersed by an extinct megafauna and having present-day interactions with surrogate frugivorous animals. The dataset, and additional information, for this study is available here.
Seed dispersal ecology: Prunus mahaleb	I am involved in a long term analysis of the seed dispersal system of Prunus mahaleb, a rosaceous treelet inhabiting the mountains of SE Spain. My main study area is located in the Sierra de Cazorla, Segura y las Villas, Jaén province. My main reserach focuses on the net effects of the mutualistic interaction with animal frugivores, which include birds and mammals. I am interested in the demographic, genetic, and evolutionary effects of the interaction. I started studying the system in 1980, and have continued working on it in collaboration with Eugene W. Schupp, since 1988. My long term monitoring involves study of fruiting intensity, phenology, seed rain patterns, tree growth, and phenotypic variation in seed mass. I am studying variation in these variables for 75 trees, with data starting in 1988.
Molecular ecology of seed dissemination by animals	A long-standing challenge in studies of seed dispersal by animal frugivores has been the characterization of the spatial relationships between dispersed seeds and the maternal plants, i.e., the seed shadow. The difficulties to track unambiguously the origin of frugivore-dispersed seeds in natural communities has been considered an unavoidable limitation of the research field and precluded a robust analysis of the direct consequences of zoochory. Together with José A. Godoy, we are using the multilocus genotype at SSR (microsatellite) loci of the woody endocarp, a seed tissue of maternal origin, to provide an unequivocal genetic fingerprint of the source tree. By comparing the endocarp genotype against the complete set of genotypes of reproductive trees in a population, we were able to unambiguously identify the source tree for 82.1 % of the seeds collected in seed traps and hypothesized that the remaining 17.9 % of sampled seeds come from other populations. Identification of the source tree for Prunus mahaleb seeds dispersed by frugivores revealed a marked heterogeneity in the genetic composition of the seed rain in different microhabitats, with a range of 1-5 distinct maternal trees contributing seeds to a particular landscape patch. Within-population dispersal distances ranged between 0-912 m, with up to 62 % of the seeds delivered within 15 m of the source trees. We are interested in the ecological and evolutioary implications of our results, indicating strong distance limitation of seed delivery combined with infrequent long-distance dispersal events, extreme heterogeneity in the landscape pattern of genetic makeup, and a marked mosaic of multiple parentage for the seeds delivered to a particular patch. A detailed description of our field methods and lab protocols is available here.
Ecological and demographic consequences of seed dispersal by frugivorous animals	The activity of frugivorous animals that disperse seeds has delayed consequences for plant demography. These consequences translate through the series of concatenated stages in plant recruitment that include seed delivery, survival to post-dispersal seed predators, seed germination, early seedling establishment, seedling survival up to sapling stage, and adult establishment. This is so because it matters not only how many seeds are dipsersed by frugivores, but where the seeds are delivered and which are the concatenated probabilities of survival for these seeds in particular microhabitat patches that differ in quality for recruitment after dispersal. The figure illustrates an structural equation model fitted to the sequential probabilities of recruitment of Phillyrea latifolia in Mediterranean montane scrubland, SE Spain. The path model depicts the multiple and delayed influences, both direct and indirect, of frugivore-mediated seed-rain on later stages of recruitment. Together with Juan-Luis García Castaño and Eugene W. Schupp, we are using this explicitly demographic approach to understand the multiple influences of frugivore activity on plant demography.
Mutualistic interactions of frugivorous animals and plants in Mediterranean-type vegetation	This is my primary research line, started in 1979, which, over the time, has unfolded in the different research interests outlined in the paragraphs above. Mediterranean-type vegetation has physiognomic and biotic characteristics similar to some subtropical and tropical forests. Among them, the most relevant to me is the ubiquity and importance of interactions with animals in the reproductive cycle of plant species, especially the woody species. Around 45%, and up to 62%, of the woody species in a particular site are dispersed by animal frugivores. This mutualistic plant-frugivore interaction is thus a key element to understand the evolution and maintenance of diversity in these shrublands. Among frugivores, small passerine birds which are wintering migrants dominate; a rich and abundant production of fleshy fruits is thus a central element for them, a keystone resource to understand the organization of their annual cycle and the evolution of migration. My research has focused on both studies at the community level (starting with my PhD) and specific analyses of particular species. Among the plants my favorite species have been Rubus ulmifolius, Pistacia lentiscus, Olea europaea, and Prunus mahaleb. Among the frugivores, I've focused on the Sylvia warblers and thrushes, Turdus species.