Biodiversity inhibits species' evolutionary responses to changing environments.

Despite growing interplay between ecological and evolutionary studies, the question of how biodiversity influences evolutionary dynamics within species remains understudied. Here, using a classical model of phenotypic evolution in species occupying a patchy environment, but introducing global change affecting patch conditions, we show that biodiversity can inhibit species' evolution during global change. The presence of several species increases the chance that one or more species are pre-adapted to new conditions, which restricts the ecological opportunity for evolutionary responses in all the species. Consequently, environmental change tends to select for changes in species abundances rather than for changing phenotypes within each species. The buffering effects of species diversity that we describe might be one important but neglected explanation for widely observed niche conservatism in natural systems. Furthermore, the results show that attempts to understand biotic responses to environmental change need to consider both ecological and evolutionary processes in a realistically diverse setting.

Evolutionary rates and species diversity in flowering plants.

Genetic change is a necessary component of speciation, but the relationship between rates of speciation and molecular evolution remains unclear. We use recent phylogenetic data to demonstrate a positive relationship between species numbers and the rate of neutral molecular evolution in flowering plants (in both plastid and nuclear genes). Rates of protein and morphological evolution also correlate with the neutral substitution rate, but not with species numbers. Our findings reveal a link between the rate of neutral molecular change within populations and the evolution of species diversity.

Phylogenetics and speciation.

Species-level phylogenies derived from molecular data provide an indirect record of the speciation events that have led to extant species. This offers enormous potential for investigating the general causes and rates of speciation within clades. To make the most of this potential, we should ideally sample all the species in a higher group, such as a genus, ensure that those species reflect evolutionary entities within the group, and rule out the effects of other processes, such as extinction, as explanations for observed patterns. We discuss recent practical and theoretical advances in this area and outline how future work should benefit from incorporating data from genealogical and phylogeographical scales.

The effect of habitat type on speciation rates and range movements in aquatic beetles: inferences from species-level phylogenies.

Most aquatic beetles in the family Dytiscidae are tightly associated either with running (lotic) or stagnant (lentic) water bodies. The range size of lotic species is known to be, on average, much smaller than that of lentic species, presumably as a result of differences in dispersal strategies in each habitat type. We explored possible effects of these differences on clade evolution and speciation rates by comparing species-level phylogenies based on cytochrome oxidase I (COI) and 16S rRNA mitochondrial genes for two genera, the lentic Ilybius and the lotic Deronectes. The expectation that species turnover is higher in lotic lineages due to their lower dispersal propensity compared to lentic species was not strongly supported. Deronectes displays a higher frequency of recent splits than Ilybius, consistent with the hypothesis, but the difference was not significant compared to expected patterns under a constant speciation rate null model. Similarly, when the degree of sympatry was plotted against relative node age, more allopatric splits were evident in the lentic Deronectes, suggesting a slower rate of range movement since speciation, but the differences were not significant. We discuss two explanations for our failure to detect differences between the two clades. First, current methods for analysing species-level phylogenies may be sensitive to taxonomic and sampling artefacts. Second, lentic and lotic clades may indeed display similar levels of species turnover despite occupying very different habitats at different spatial scales. More work is needed to investigate the effects of population level processes and spatial scale on macroevolutionary dynamics.

Species richness: does flower power explain beetle-mania?

The huge species richness of beetles has been attributed to their colonisation of flowering plants, but a vegetarian diet may not be the sole secret of the beetles' success.