The Evolution of Functionally Redundant Species; Evidence from Beetles

While species fulfill many different roles in ecosystems, it has been suggested that numerous species might actually share the same function in a near neutral way. So-far, however, it is unclear whether such functional redundancy really exists. We scrutinize this question using extensive data on the world’s 4168 species of diving beetles. We show that across the globe these animals have evolved towards a small number of regularly-spaced body sizes, and that locally co-existing species are either very similar in size or differ by at least 35%. Surprisingly, intermediate size differences (10–20%) are rare. As body-size strongly reflects functional aspects such as the food that these generalist predators can eat, these beetles thus form relatively distinct groups of functional look-a-likes. The striking global regularity of these patterns support the idea that a self-organizing process drives such species-rich groups to self-organize evolutionary into clusters where functional redundancy ensures resilience through an insurance effect

Testing niche-based and neutral mechanisms of species coexistence

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Data from: Complex relationships between competing guilds along large-scale environmental gradients

Despite much research over the past 30 years, there is still little general understanding of how the outcomes of interactions vary along environmental gradients, particularly at large geographic scales. A simple expectation is that decreasing environmental quality should reduce densities of competitors and hence the effects of competition should weaken in poorer environments. A counterintuitive consequence is that associations between densities of competitors might change from negative to positive as environments decrease in quality. Here we test these predictions in a set of vascular plant communities where perennial species share space and resources with less competitive annuals. We surveyed nine gray dune communities annually for 5 years along a cross-European latitudinal gradient of habitat quality. We find that densities of annual and perennial species are negatively correlated at the high-quality end of the gradient, while at the low-quality end, guild densities are uncorrelated or positively correlated, consistent with a weakening of competition linked to increasing environmental limitations. Our results suggest that even simple interactions can give rise to nonobvious changes in species associations along environmental gradients. They highlight that understanding the outcome of species interactions may require explicit characterization of their changing intensity with environmental quality and that the factors limiting species’ codistribution can vary along environmental gradients

Link to GenBank accession numbers for phylogeny in appendix Figure B1

Excel file containing the link to GenBank accession numbers for phylogeny in appendix Figure B1. This figure is based on the phylogeny presented in Leijs et al. 2012, PLoS ONE, vol 7

Data from: Repeated parallel evolution reveals limiting similarity in subterranean diving beetles

The theory of limiting similarity predicts that co-occurring species must be sufficiently different to coexist. Although this idea is a staple of community ecology, convincing empirical evidence has been scarce. Here we examine 34 subterranean beetle communities in arid inland Australia that share the same habitat type but have evolved in complete isolation over the past 5 million years. Although these communities come from a range of phylogenetic origins, we find that they have almost invariably evolved to share a similar size structure. The relative positions of coexisting species on the body size axis were significantly more regular across communities than would be expected by chance, with a size ratio, on average, of 1.6 between coexisting species. By contrast, species’ absolute body sizes varied substantially from one community to the next. This suggests that self-organized spacing according to limiting-similarity theory, as opposed to evolution toward preexisting fixed niches, shaped the communities. Using a model starting from random sets of founder species, we demonstrate that the patterns are indeed consistent with evolutionary self-organization. For less isolated habitats, the same model predicts the coexistence of multiple species in each regularly spaced functional group. Limiting similarity, therefore, may also be compatible with the coexistence of many redundant species

Raw annual and perennial abundance data

This data set contains annual abundances for all sites and all years (2008-2012) as well as perennial heights in cms (2009-2012) and perennial ground covers as percentages (2008-2012). It also contains a column called "relationship" which shows the type of relationship found between annual abundances and perennial heights (one of positive, negative or quadratic) according to the method described in the paper. This data was used to produce figures 4, 5, 6, B2 and B4

Environmental data along the latitudinal gradient

This file contains data on the abiotic and biotic conditions experienced by both annual and perennial guilds along the sampled latitudinal gradient. Variables include mean rainfall in mm, temperatures in degree celcius (mean monthly maximum, mean monthly minimum, mean daily), mean sunshine hours in autumn, spring and winter, mean number of rabbit faecal pellets (a proxy for grazing intensity), mean soil nitrogen concentration, as well as mean bryophyte ground cover and mat thickness, and mean correlation between annual abundances and bryophyte ground cover. This data was used to produce figures 3, B1 and B3

Body size data of Australian diving beetles

Excel file containing 1) body sizes of individuals of diving beetle species collected in the field, 2) body size ranges for additional beetle species, taken from Watts and Humphreys 200