Trait evolution, resource specialization and vulnerability to plant extinctions among Antillean hummingbirds.

Species traits are thought to predict feeding specialization and the vulnerability of a species to extinctions of interaction partners, but the context in which a species evolved and currently inhabits may also matter. Notably, the predictive power of traits may require that traits evolved to fit interaction partners. Furthermore, local abiotic and biotic conditions may be important. On islands, for instance, specialized and vulnerable species are predicted to be found mainly in mountains, whereas species in lowlands should be generalized and less vulnerable. We evaluated these predictions for hummingbirds and their nectar-food plants on Antillean islands. Our results suggest that the rates of hummingbird trait divergence were higher among ancestral mainland forms before the colonization of the Antilles. In correspondence with the limited trait evolution that occurred within the Antilles, local abiotic and biotic conditions-not species traits-correlate with hummingbird resource specialization and the vulnerability of hummingbirds to extinctions of their floral resources. Specifically, hummingbirds were more specialized and vulnerable in conditions with high topographical complexity, high rainfall, low temperatures and high floral resource richness, which characterize the Antillean Mountains. These findings show that resource specialization and species vulnerability to extinctions of interaction partners are highly context-dependent.

Relicts of the lost arc: High-throughput sequencing of the Eutrichomyias rowleyi (Aves: Passeriformes) holotype uncovers an ancient biogeographic link between the Philippines and Fiji.

Molecular studies have revealed a number of cases in which traditional assessments of evolutionary relationships have been incorrect. This has implications not only for systematics and taxonomy but also for our understanding of how diversity patterns on Earth have been formed. Here, we use high-throughput sequencing technology to obtain molecular data from the holotype specimen of the elusive Eutrichomyias rowleyi, which is endemic to the Indonesian island of Sangihe. We show that E. rowleyi unexpectedly is a member of the family Lamproliidae, which dates back some 20 Million years and only include two other species, Lamprolia victoriae from Fiji and Chaetorhynchus papuensis from New Guinea. Tectonic reconstructions suggest that the Melanesian island arc, which included land masses on the northern edge of the Australian plate (present day New Guinea) stretched as a string of islands from the Philippines (including proto-Sangihe) to Fiji from 25 to 20 My. Consequently, our results are indicative of an ancient distribution along the Melanesian island arc followed by relictualization, which led to members of the Lamproliidae to be distributed on widely separated islands across the Indo-Pacific.

Historical Biogeography and Extinction in the Hawaiian Honeycreepers.

Hawaiian honeycreepers, comprising an endemic radiation of passerine birds in the Hawaiian archipelago, have suffered losses of individual island populations and the extinction of many species as a result of colonization of the islands by Polynesians and, more recently, introduced avian pox virus and avian malaria. Here, I test the idea that populations have an intrinsic tendency toward extinction regardless of the cause. The distribution of each species before the arrival of humans in the archipelago was inferred from present distribution, historical records, and fossil remains. On the basis of these records, each species was placed in one of four stages of the taxon cycle: (1) expanding or recently expanded, (2) differentiating, (3) fragmenting, or (4) single-island endemic. Subsequent extinction of individual island populations was most frequent in stage 3 species, which had already suffered loss of individual island populations, suggesting commonality in vulnerability to extinction from anthropogenic and nonanthropogenic causes.

Emergence of evolutionary cycles in size-structured food webs.

The interplay of population dynamics and evolution within ecological communities has been of long-standing interest for ecologists and can give rise to evolutionary cycles, e.g. taxon cycles. Evolutionary cycling was intensely studied in small communities with asymmetric competition; the latter drives the evolutionary processes. Here we demonstrate that evolutionary cycling arises naturally in larger communities if trophic interactions are present, since these are intrinsically asymmetric. To investigate the evolutionary dynamics of a trophic community, we use an allometric food web model. We find that evolutionary cycles emerge naturally for a large parameter ranges. The origin of the evolutionary dynamics is an intrinsic asymmetry in the feeding kernel which creates an evolutionary ratchet, driving species towards larger bodysize. We reveal different kinds of cycles: single morph cycles, and coevolutionary and mixed cycling of complete food webs. The latter refers to the case where each trophic level can have different evolutionary dynamics. We discuss the generality of our findings and conclude that ongoing evolution in food webs may be more frequent than commonly believed.

Taxon Cycles in Neotropical Mangroves.

The concept of the taxon cycle involves successive range expansions and contractions over time, through which a species can indefinitely maintain its core distribution. Otherwise, it becomes extinct. Taxon cycles have been defined mostly for tropical island faunas; examples from continental areas are scarce, and similar case studies for plants remain unknown. Most taxon cycles have been identified on the basis of phylogeographic studies, and straightforward empirical evidence from fossils is lacking. Here, empirical fossil evidence is provided for the recurrent Eocene to the present expansion/contraction cycles in a mangrove taxon (Pelliciera) after a Neotropical-wide study of the available pollen records. This recurrent behavior is compatible with the concept of the taxon cycle from biogeographical, chronological and ecological perspectives. The biotic and abiotic drivers potentially involved in the initiation and maintenance of the Pelliciera expansion/contraction cycles are analyzed, and the ecological and evolutionary implications are discussed. Whether this could be a trend toward extinction is considered under the predictions of the taxon cycle theory. The recurrent expansion and contraction cycles identified for Pelliciera have strong potential for being the first empirically and unequivocally documented taxon cycles and likely the only taxon cycles documented to date for plants.

MODELS OF CHARACTER DISPLACEMENT AND THE THEORETICAL ROBUSTNESS OF TAXON CYCLES.

The appropriateness of the techniques used in modeling character displacement has been the focus of vigorous debate. In this paper, the three competing methods (the coevolutionarily stable community (CSC), the evolutionarily stable strategy (ESS), and quantitative genetic recursion (QGR)) are compared in models using a common ecological setting. Specific predictions of the CSC model have been used to understand features of character displacement among Cnemidophorous lizards on islands off Mexico, Anolis lizards in the Lesser Antilles and Galápagos finches. Nonetheless, the validity of the approach has been repeatedly questioned. Conceptually the three formalisms vary in the degree to which within species variability is allowed in the models. The predictions of the CSC are found not to be robust to even small violation of its fundamental assumption of absolute species monomorphy. We show by simulation and analytical observations that the CSC is not valid under frequency dependent selection, and that the ESS is the limiting case of QGR as intraspecific phenotypic variation goes to zero. Thus the ESS and the QGR models agree closely when the between-phenotype component (BPC) of the niche width is small. However, as the BPC increases, quantitative discrepancies between ESS and QGR predictions increase, although model behavior remains qualitatively similar. A fourth approach, termed "Quantitative Genetic Optimization" (QGO) analysis, is suggested, combining advantages of both the ESS and QGR. Although all approaches support the possibility of taxon cycles, the cycle patterns predicted are qualitatively different and strongly model dependent.