Ecology Letters

Arita, Héctor T.; Vázquez‐Domínguez, Ella

doi: 10.1111/j.1461-0248.2008.01197.xpmid: 18445032

Several ecological and evolutionary hypotheses have been proposed to explain the latitudinal diversity gradient (LDG), but a general model for this conspicuous pattern remains elusive. Mid‐domain effect (MDE) models generate gradients of species diversity by randomly placing the geographic ranges of species in one‐ or two‐dimensional spaces, thus excluding both evolutionary processes and the effect of contemporary climate. Traditional MDE models are statistical and static because they determine the size of ranges either randomly or based on empirical frequency distributions. Here we present a simple dynamic null model for the LDG that simulates stochastic processes of range shifts, extinction and speciation. The model predicts higher species diversity and higher extinction and speciation rates in the tropics, and a strong influence of range movements in shaping the LDG. These null expectations should be taken into consideration in studies aimed at understanding the many factors that generate latitudinal diversity gradients.

Jones, Owen R.; Gaillard, Jean‐Michel; Tuljapurkar, Shripad; Alho, Jussi S.; Armitage, Kenneth B.; Becker, Peter H.; Bize, Pierre; Brommer, Jon; Charmantier, Anne; Charpentier, Marie; Clutton‐Brock, Tim; Dobson, F. Stephen; Festa‐Bianchet, Marco; Gustafsson, Lars;

Diez, Jeffrey M.; Sullivan, Jon J.; Hulme, Philip E.; Edwards, Grant; Duncan, Richard P.

doi: 10.1111/j.1461-0248.2008.01178.xpmid: 18400019

Darwin acknowledged contrasting, plausible arguments for how species invasions are influenced by phylogenetic relatedness to the native community. These contrasting arguments persist today without clear resolution. Using data on the naturalization and abundance of exotic plants in the Auckland region, we show how different expectations can be accommodated through attention to scale, assumptions about niche overlap, and stage of invasion. Probability of naturalization was positively related to the number of native species in a genus but negatively related to native congener abundance, suggesting the importance of both niche availability and biotic resistance. Once naturalized, however, exotic abundance was not related to the number of native congeners, but positively related to native congener abundance. Changing the scale of analysis altered this outcome: within habitats exotic abundance was negatively related to native congener abundance, implying that native and exotic species respond similarly to broad scale environmental variation across habitats, with biotic resistance occurring within habitats.

Reber, Anabelle; Castella, Grégoire; Christe, Philippe; Chapuisat, Michel

doi: 10.1111/j.1461-0248.2008.01177.xpmid: 18371089

A leading hypothesis linking parasites to social evolution is that more genetically diverse social groups better resist parasites. Moreover, group diversity can encompass factors other than genetic variation that may also influence disease resistance. Here, we tested whether group diversity improved disease resistance in an ant species with natural variation in colony queen number. We formed experimental groups of workers and challenged them with the fungal parasite Metarhizium anisopliae. Workers originating from monogynous colonies (headed by a single queen and with low genetic diversity) had higher survival than workers originating from polygynous ones, both in uninfected groups and in groups challenged with M. anisopliae. However, an experimental increase of group diversity by mixing workers originating from monogynous colonies strongly increased the survival of workers challenged with M. anisopliae, whereas it tended to decrease their survival in absence of infection. This experiment suggests that group diversity, be it genetic or environmental, improves the mean resistance of group members to the fungal infection, probably through the sharing of physiological or behavioural defences.

Carvalheiro, Luisa G.; Buckley, Yvonne M.; Ventim, Rita; Fowler, Simon V.; Memmott, Jane

doi: 10.1111/j.1461-0248.2008.01184.xpmid: 18422636

Despite current concern about the safety of biological control of weeds, assessing the indirect impacts of introduced agents is not common practice. Using 17 replicate food webs, we demonstrate that the use of a highly host‐plant specific weed biocontrol agent, recently introduced into Australia, is associated with declines of local insect communities. The agent shares natural enemies (predators and parasitoids) with seed herbivore species from native plants, so apparent competition is the most likely cause for these losses. Both species richness and abundance in insect communities (seed herbivores and their parasitoids) were negatively correlated with the abundance of the biocontrol agent. Local losses of up to 11 species (dipteran seed herbivores and parasitoids) took place as the biocontrol agent abundance increased. Ineffective biocontrol agents that remain highly abundant in the community are most likely to have persistent, indirect negative effects. Our findings suggest that more investment is required in pre‐release studies on the effectiveness of biocontrol agents, as well as in post‐release studies assessing indirect impacts, to avoid or minimize the release of potentially damaging species.

Dlugosch, Katrina M.; Parker, Ingrid M.

doi: 10.1111/j.1461-0248.2008.01181.xpmid: 18410377

Human‐mediated species introductions offer opportunities to investigate when and how non‐native species to adapt to novel environments, and whether evolution has the potential to contribute to colonization success. Many long‐established introductions harbour high genetic diversity, raising the possibility that multiple introductions of genetic material catalyze adaptation and/or the evolution of invasiveness. Studies of nascent invasions are rare but crucial for understanding whether genetic diversity facilitates population expansion. We explore variation and evolution in founder populations of the invasive shrub Hypericum canariense. We find that these introductions have experienced large reductions in genetic diversity, but that increased growth and a latitudinal cline in flowering phenology have nevertheless evolved. These life history changes are consistent with predictions for invasive plants. Our results highlight the potential for even genetically depauperate founding populations to adapt and evolve invasive patters of spread.

McCoy, Michael W.; Gillooly, James F.

doi: 10.1111/j.1461-0248.2008.01190.xpmid: 18422635

Understanding the factors that control the mortality rates of species in their natural environments is important for understanding the structure and dynamics of populations, communities and ecosystems. Here, we test a model of natural mortality that yields explicit, quantitative predictions based on the constraints of body size and temperature on individual metabolism. Extensive field data from plants, invertebrates, fish, birds and mammals indicate that much of the heterogeneity in rates of natural mortality can be predicted, despite the many extrinsic sources of mortality in natural systems. These results suggest that common ‘rule(s)’ govern mortality rates in ecological communities for organisms as diverse as plants and animals.

Questad, Erin J.; Foster, Bryan L.

doi: 10.1111/j.1461-0248.2008.01186.xpmid: 18445035

The effect of spatial heterogeneity on species coexistence relies on the degree of niche heterogeneity in the habitat and the ability of species to exploit the available niche opportunities. We studied species coexistence in a perennial grassland, and tested whether small‐scale disturbances create environmental heterogeneity that affects coexistence and whether the functional diversity of species in the species pool affects the ability of community composition to reflect heterogeneity through species sorting. We manipulated the spatio‐temporal heterogeneity of disturbance and the functional diversity of species added as seed and measured their impact on the spatial turnover of species composition. Disturbance increased environmental heterogeneity and spatial turnover, and the effect of heterogeneity on turnover was greatest in the presence of a functionally diverse species pool, showing the importance of trait variation among species for exploiting environmental heterogeneity, and suggesting that coexistence occurred due to species sorting among heterogeneous niches.

Karban, Richard

doi: 10.1111/j.1461-0248.2008.01183.xpmid: 18400016

Plant behaviours are defined as rapid morphological or physiological responses to events, relative to the lifetime of an individual. Since Darwin, biologists have been aware that plants behave but it has been an underappreciated phenomenon. The best studied plant behaviours involve foraging for light, nutrients, and water by placing organs where they can most efficiently harvest these resources. Plants also adjust many reproductive and defensive traits in response to environmental heterogeneity in space and time. Many plant behaviours rely on iterative active meristems that allow plants to rapidly transform into many different forms. Because of this modular construction, many plant responses are localized although the degree of integration within whole plants is not well understood. Plant behaviours have been characterized as simpler than those of animals. Recent findings challenge this notion by revealing high levels of sophistication previously thought to be within the sole domain of animal behaviour. Plants anticipate future conditions by accurately perceiving and responding to reliable environmental cues. Plants exhibit memory, altering their behaviours depending upon their previous experiences or the experiences of their parents. Plants communicate with other plants, herbivores and mutualists. They emit cues that cause predictable reactions in other organisms and respond to such cues themselves. Plants exhibit many of the same behaviours as animals even though they lack central nervous systems. Both plants and animals have faced spatially and temporally heterogeneous environments and both have evolved plastic response systems.

Gruner, Daniel S.; Smith, Jennifer E.; Seabloom, Eric W.; Sandin, Stuart A.; Ngai, Jacqueline T.; Hillebrand, Helmut; Harpole, W. Stanley; Elser, James J.; Cleland, Elsa E.; Bracken, Matthew E. S.; Borer, Elizabeth T.; Bolker, Benjamin M.