Stability of ecological communities and the architecture of mutualistic and trophic networks.

Research on the relationship between the architecture of ecological networks and community stability has mainly focused on one type of interaction at a time, making difficult any comparison between different network types. We used a theoretical approach to show that the network architecture favoring stability fundamentally differs between trophic and mutualistic networks. A highly connected and nested architecture promotes community stability in mutualistic networks, whereas the stability of trophic networks is enhanced in compartmented and weakly connected architectures.

Distorted views of biodiversity: spatial and temporal bias in species occurrence data.

Boakes et al. compile and analyze a historical dataset of 170,000 bird sightings over two centuries and show how changing trends in data gathering may confound a true picture of biodiversity change.

Differences in spawning date between populations of common frog reveal local adaptation.

Phenotypic differences between populations often correlate with climate variables, resulting from a combination of environment-induced plasticity and local adaptation. Species comprising populations that are genetically adapted to local climatic conditions should be more vulnerable to climate change than those comprising phenotypically plastic populations. Assessment of local adaptation generally requires logistically challenging experiments.

Speciation has a spatial scale that depends on levels of gene flow.

Area is generally assumed to affect speciation rates, but work on the spatial context of speciation has focused mostly on patterns of range overlap between emerging species rather than on questions of geographical scale. A variety of geographical theories of speciation predict that the probability of speciation occurring within a given region should (1) increase with the size of the region and (2) increase as the spatial extent of intraspecific gene flow becomes smaller. Using a survey of speciation events on isolated oceanic islands for a broad range of taxa, we find evidence for both predictions.

Some methodological issues in macroecology.

Recent years have seen the emergence of "macroecology" as a distinct research program in biology. It is concerned with geographical scale patterns in assemblage structure and, as such, of necessity relies heavily on approaches that are nonexperimental and that depend on the availability of reliable information for large numbers of species. This gives rise to a particular set of analytical issues that need to be addressed when conducting studies of macroecological patterns.

Coexistence and relative abundance in annual plant assemblages: the roles of competition and colonization.

Although an interspecific trade-off between competitive and colonizing ability can permit multispecies coexistence, whether this mechanism controls the structure of natural systems remains unresolved. We used models to evaluate the hypothesized importance of this trade-off for explaining coexistence and relative abundance patterns in annual plant assemblages. In a nonspatial model, empirically derived competition-colonization trade-offs related to seed mass were insufficient to generate coexistence.

Snow tussocks, chaos, and the evolution of mast seeding.

One hitherto intractable problem in studying mast seeding (synchronous intermittent heavy flowering by a population of perennial plants) is determining the relative roles of weather, plant reserves, and evolutionary selective pressures such as predator satiation. We parameterize a mechanistic resource-based model for mast seeding in Chionochloa pallens (Poaceae) using a long-term individually structured data set. Each plant's energy reserves were reconstructed using annual inputs (growing degree days), outputs (flowering), and a novel regression technique.

Are plants really larger in their introduced ranges?

The "rule" that individuals of nonindigenous plant species are larger where they are introduced than where they are native is not borne out in detailed comparisons of European species introduced to California or the Carolinas and species from California and the Carolinas introduced to Europe. On average, individuals of California species are taller in California than in Europe, while individuals of species native to Europe do not differ between Europe and California. Similarly, individuals of species from the Carolinas are, on average, taller in the Carolinas than in Europe, while individuals of European species are the same height in Europe and the Carolinas or, depending on the nature of the statistical analysis, taller in Europe.

Nitrogen enrichment modifies plant community structure via changes to plant-soil feedback.

We tested the hypothesis that N enrichment modifies plant-soil feedback relationships, resulting in changes to plant community composition. This was done in a two-phase glasshouse experiment. In the first phase, we grew eight annual plant species in monoculture at two levels of N addition.

Sympatric speciation in birds is rare: insights from range data and simulations.

Sympatric speciation is now accepted as theoretically plausible and a likely explanation for divergence in a handful of taxa, but its contribution to large-scale patterns of speciation remains contentious. A major problem is that it is difficult to differentiate between alternate scenarios of geographic speciation when species ranges have shifted substantially in the past. Previous studies have searched for a signal of the geographic mode of speciation by testing for a correlation between time since speciation and range overlap.

Density-dependent cladogenesis in birds.

A characteristic signature of adaptive radiation is a slowing of the rate of speciation toward the present. On the basis of molecular phylogenies, studies of single clades have frequently found evidence for a slowdown in diversification rate and have interpreted this as evidence for density dependent speciation. However, we demonstrated via simulation that large clades are expected to show stronger slowdowns than small clades, even if the probability of speciation and extinction remains constant through time.

Application of the lumped age-class technique to studying the dynamics of malaria-mosquito-human interactions.

A series of models of malaria-mosquito-human interactions using the Lumped Age-Class technique of Gurney & Nisbet are developed. The models explicitly include sub-adult mosquito dynamics and assume that population regulation occurs at the larval stage. A challenge for modelling mosquito dynamics in continuous time is that the insect has discrete life-history stages (egg, larva, pupa & adult), the sub-adult stages of relatively fixed duration, which are subject to very different demographic rates.

Biogeographical basis of recent phenotypic divergence among birds: a global study of subspecies richness.

Theory predicts that biogeographic factors should play a central role in promoting population divergence and speciation. Previous empirical studies into biogeography and diversification have been relatively restricted in terms of the geographical area, phylogenetic scope, and the range of biogeographic factors considered. Here we present a global analysis of allopatric phenotypic divergence (measured as subspecies richness) across more than 9600 bird species.

Seed dispersal and spatial pattern in tropical trees.

Theories of tropical tree diversity emphasize dispersal limitation as a potential mechanism for separating species in space and reducing competitive exclusion. We compared the dispersal morphologies, fruit sizes, and spatial distributions of 561 tree species within a fully mapped, 50-hectare plot of primary tropical forest in peninsular Malaysia. We demonstrate here that the extent and scale of conspecific spatial aggregation is correlated with the mode of seed dispersal.

Decoupling the direct and indirect effects of nitrogen deposition on ecosystem function.

Elevated nitrogen (N) inputs into terrestrial ecosystems are causing major changes to the composition and functioning of ecosystems. Understanding these changes is challenging because there are complex interactions between 'direct' effects of N on plant physiology and soil biogeochemistry, and 'indirect' effects caused by changes in plant species composition. By planting high N and low N plant community compositions into high and low N deposition model terrestrial ecosystems we experimentally decoupled direct and indirect effects and quantified their contribution to changes in carbon, N and water cycling.

Ecology predicts large-scale patterns of phylogenetic diversification in birds.

One of the most striking patterns in evolutionary biology is that clades may differ greatly in the number of species they contain. Numerous hypotheses have been put forward to explain this phenomenon, and several have been tested using phylogenetic methods. Remarkably, however, all such tests performed to date have been characterized by modest explanatory power, which has generated an interest in explanations stressing the importance of random processes.

Latent extinction risk and the future battlegrounds of mammal conservation.

Global conservation prioritization usually emphasizes areas with highest species richness or where many species are thought to be at imminent risk of extinction. However, these strategies may overlook areas where many species have biological traits that make them particularly sensitive to future human impact but are not yet threatened because such impact is currently low. In this article, we identify such areas for the world's mammals using latent extinction risk, the discrepancy between a species' current extinction risk and that predicted from models on the basis of biological traits.

Aphid protected from pathogen by endosymbiont.

Aphids are associated with several facultative bacterial endosymbionts that may influence their interactions with other organisms. We show here that one of the three most common facultative symbionts of pea aphid (Acyrthosiphon pisum), the bacterium Regiella insecticola, has a major effect on host resistance to a fungal pathogen. Experimental establishment of the bacterium in uninfected aphid clones led to higher survival after fungal attack.

Local spatial structure and predator-prey dynamics: counterintuitive effects of prey enrichment.

The Lotka-Volterra predator-prey model with prey density dependence shows the final prey density to be independent of its vital rates. This result assumes the community to be well mixed so that encounters between predators and prey occur as a product of the landscape densities, yet empirical evidence suggests that over small spatial scales this may not be the normal pattern. Starting from an individual-based model with neighborhood interactions and movements, a deterministic approximation is derived, and the effect of local spatial structure on equilibrium densities is investigated.

Evolutionary change in parasitoid resistance under crowded conditions in Drosophila melanogaster.

Patterns of investment of limiting resources in such processes as competing for food and defense against natural enemies are shaped by trade-offs and constraints. In Drosophila melanogaster artificial selection for increased resistance to parasitoids results in a correlated decrease in larval competitive ability. Here we ask whether selection for competitive ability leads to a correlated reduction in parasitoid resistance.

The effect of recycling on plant competitive hierarchies.

Evidence from field studies suggests that some plant species enhance their persistence by reinforcing patterns of N availability through differences in litter quality. Using mathematical models of nutrient flow, we explore whether and how recycling affects plant growth, competition, and coexistence and whether it leads to positive feedbacks. Two mechanisms are considered: the ability of plants to access two forms of soil N, complex (e.

Periodic local disturbance in host-parasitoid metapopulations: host suppression and parasitoid persistence.

Within many agricultural systems, insect pests and their natural enemies are forced to persist as a metapopulation, continuously recolonizing patches following disturbance through harvesting or spraying with insecticides. Despite the need to understand factors influencing biocontrol success, few theoretical studies of host-parasitoid interactions have examined the potential impact of local disturbance within a metapopulation framework. Here, we add periodic local mortality to series of classical host-parasitoid models to examine its effect on host suppression and parasitoid persistence.

Darwin's abominable mystery: Insights from a supertree of the angiosperms.

Angiosperms are among the major terrestrial radiations of life and a model group for studying patterns and processes of diversification. As a tool for future comparative studies, we compiled a supertree of angiosperm families from published phylogenetic studies. Sequence data from the plastid rbcL gene were used to estimate relative timing of branching events, calibrated by using robust fossil dates.

The effects of enrichment on the dynamics of apparent competitive interactions in stage-structured systems.

In the absence of other limiting factors, assemblages in which species share a common, effective natural enemy are not expected to persist. Although a variety of mechanisms have been postulated to explain the coexistence of species that share natural enemies, the role of productivity gradients has not been explored in detail. Here, we examine how enrichment can affect the outcome of apparent competition.