Ecology Letters

Wiens, John J.; Cornell, Howard

doi: 10.1111/ele.12503pmid: 26346782

Terrestrial environments occupy ~ 30% of the Earth's surface yet contain ~ 80% of all species. The causes of this dramatic biodiversity gradient have remained relatively unstudied. Here, I test the fundamental prediction that predominantly non‐marine clades have more rapid rates of diversification than marine clades, using a time‐calibrated phylogeny of animal phyla. The results strongly support this hypothesis. This pattern helps explain the higher richness of terrestrial environments and the dramatic variation in species richness among animal phyla. The results show the importance of ecology in explaining large‐scale patterns of clade richness and of diversification rates in explaining Earth's largest biodiversity patterns. The results also demonstrate remarkable niche conservatism in habitats, in some cases lasting > 800 million years. Finally, the results highlight the surprisingly high species richness of freshwater habitats, which are nearly equal to marine environments despite their much smaller area (~ 2% of Earth's surface vs. 70% for marine habitats).

Fleming‐Davies, Arietta E.; Dukic, Vanja; Andreasen, Viggo; Dwyer, Greg; Lafferty, Kevin

doi: 10.1111/ele.12506pmid: 26365355

Phenotypic variation is common in most pathogens, yet the mechanisms that maintain this diversity are still poorly understood. We asked whether continuous host variation in susceptibility helps maintain phenotypic variation, using experiments conducted with a baculovirus that infects gypsy moth (Lymantria dispar) larvae. We found that an empirically observed tradeoff between mean transmission rate and variation in transmission, which results from host heterogeneity, promotes long‐term coexistence of two pathogen types in simulations of a population model. This tradeoff introduces an alternative strategy for the pathogen: a low‐transmission, low‐variability type can coexist with the high‐transmission type favoured by classical non‐heterogeneity models. In addition, this tradeoff can help explain the extensive phenotypic variation we observed in field‐collected pathogen isolates, in traits affecting virus fitness including transmission and environmental persistence. Similar heterogeneity tradeoffs might be a general mechanism promoting phenotypic variation in any pathogen for which hosts vary continuously in susceptibility.

Pintor, Lauren M.; Byers, James E.; Anderson, Marti

doi: 10.1111/ele.12496pmid: 26303824

Despite knowledge on invasive species’ predatory effects, we know little of their influence as prey. Non‐native prey should have a neutral to positive effect on native predators by supplementing the prey base. However, if non‐native prey displace native prey, then an invader's net influence should depend on both its abundance and value relative to native prey. We conducted a meta‐analysis to quantify the effect of non‐native prey on native predator populations. Relative to native prey, non‐native prey similarly or negatively affect native predators, but only when studies employed a substitutive design that examined the effects of each prey species in isolation from other prey. When native predators had access to non‐native and native prey simultaneously, predator abundance increased significantly relative to pre‐invasion abundance. Although non‐native prey may have a lower per capita value than native prey, they seem to benefit native predators by serving as a supplemental prey resource.

Bestion, Elvire; Clobert, Jean; Cote, Julien; Gaillard, Jean‐Michel

doi: 10.1111/ele.12502pmid: N/A

Range shift, a widespread response to climate change, will depend on species abilities to withstand warmer climates. However, these abilities may vary within species and such intraspecific variation can strongly impact species responses to climate change. Facing warmer climates, individuals should disperse according to their thermal optimum with consequences for species range shifts. Here, we studied individual dispersal of a reptile in response to climate warming and preferred temperature using a semi‐natural warming experiment. Individuals with low preferred temperatures dispersed more from warmer semi‐natural habitats, whereas individuals with higher preferred temperatures dispersed more from cooler habitats. These dispersal decisions partly matched phenotype‐dependent survival rates in the different thermal habitats, suggesting adaptive dispersal decisions. This process should result into a spatial segregation of thermal phenotypes along species moving ranges which should facilitate local adaptation to warming climates. We therefore call for range shift models including intraspecific variation in thermal phenotype and dispersal decision.

Jones, Emily I.; Afkhami, Michelle E.; Akçay, Erol; Bronstein, Judith L.; Bshary, Redouan; Frederickson, Megan E.; Heath, Katy D.; Hoeksema, Jason D.; Ness, Joshua H.; Pankey, M. Sabrina; Porter, Stephanie S.; Sachs, Joel L.; Scharnagl, Klara; Friesen, Maren L.; Dam, Nicole

doi: 10.1111/ele.12507pmid:

Li, Ronghua; Zhu, Shidan; Chen, Han Y. H.; John, Robert; Zhou, Guoyi; Zhang, Deqiang; Zhang, Qianmei; Ye, Qing; He, Fangliang

doi: 10.1111/ele.12497pmid: 26311436

Significant changes in the composition of tree species have been observed in various forests worldwide. We hypothesised that these changes might result from variable sensitivities of species to global change, and species sensitivities might be quantified, using functional traits. Employing long‐term (1978–2010) species abundance data of 48 tree species from a permanent subtropical forest plot, where multiple global change factors have been observed, including soil drying, we examined the relationships between temporal trends in abundance and suits of functional traits. We found that species with high photosynthesis rates, leaf phosphorus and nitrogen concentrations, specific leaf area, hydraulic conductivity, turgor loss point and predawn leaf water potential had increased in abundance, while species with opposite trait patterns had decreased. Our results demonstrate that functional traits underlie tree species abundance dynamics in response to drought stress, thus linking traits to compositional shifts in this subtropical forest under global changes.

Armitage, David W.; Vellend, Mark

doi: 10.1111/ele.12501pmid: 26314690

The time–area–productivity hypothesis is a proposed explanation for global biodiversity gradients. It predicts that a bioregion's modern diversity is the product of its area and productivity, integrated over evolutionary time. I performed the first experimental test of the time–area–productivity hypothesis using a model system for adaptive radiation – the bacterium Pseudomonas fluorescens SBW25. I initiated hundreds of independent radiations under culture conditions spanning a variety of productivities, spatial extents and temporal extents. Time‐integrated productivity was the single best predictor of extant phenotypic diversity and richness. In contrast, ‘snapshots’ of modern environmental variables at the time of sampling were less useful predictors of diversity patterns. These results were best explained by marked variation in population growth parameters under different productivity treatments and the long periods over which standing diversity could persist in unproductive habitats. These findings provide the first experimental support for time‐integrated productivity as a putative driver of regional biodiversity patterns.

Ryabov, Alexey B.; Morozov, Andrew; Blasius, Bernd; Fussmann, Gregor

doi: 10.1111/ele.12521pmid: 26391624

Ecological communities are often characterised by many species occupying the same trophic level and competing over a small number of vital resources. The mechanisms maintaining high biodiversity in such systems are still poorly understood. Here, we revisit the role of prey selectivity by generalist predators in promoting biodiversity. We consider a generic tri‐trophic food web, consisting of a single limiting resource, a large number of primary producers and a generalist predator. We suggest a framework to describe the predator functional response, combining food selectivity for distinctly different functional prey groups with proportion‐based consumption of similar prey species. Our simulations reveal that intermediate levels of prey selectivity can explain a high species richness, functional biodiversity, and variability among prey species. In contrast, perfect food selectivity or purely proportion‐based food consumption leads to a collapse of prey functional biodiversity. Our results are in agreement with empirical phytoplankton rank‐abundance curves in lakes.

Villellas, Jesús; Doak, Daniel F.; García, María B.; Morris, William F.; Hille Ris Lambers, Janneke

doi: 10.1111/ele.12505pmid: 26355390

Most species are exposed to significant environmental gradients across their ranges, but vital rates (survival, growth, reproduction and recruitment) need not respond in the same direction to those gradients. Opposing vital rate trends across environments, a phenomenon that has been loosely called ‘demographic compensation’, may allow species to occupy larger geographical ranges and alter their responses to climate change. Yet the term has never been precisely defined, nor has its existence or strength been assessed for multiple species. Here, we provide a rigorous definition, and use it to develop a strong test for demographic compensation. By applying the test to data from 26 published, multi‐population demographic studies of plants, we show that demographic compensation commonly occurs. We also investigate the mechanisms by which this phenomenon arises by assessing which demographic processes and life stages are most often involved. In addition, we quantify the effect of demographic compensation on variation in population growth rates across environmental gradients, a potentially important determinant of the size of a species’ geographical range. Finally, we discuss the implications of demographic compensation for the responses of single populations and species’ ranges to temporal environmental variation and to ongoing environmental trends, e.g. due to climate change.

Ward, Colette L.; McCann, Kevin S.; Rooney, Neil; Chase, Jonathan

doi: 10.1111/ele.12498pmid: 26311533

Classical food web theory holds that energy channels are regulated by top‐down control with increasing productivity, arising from within‐channel processes. However, these hypotheses do not consider the existence of parallel energy channels linked by shared resource pools and which can fuel generalist predators, imposing trophic control arising from multi‐channel processes. Using 23 large marine food webs, we show that food web responses to increasing productivity are consistent with the apparent trophic cascade hypothesis (ATCH) – with rising productivity predators derive an increasing fraction of their diet from increasingly productive bottom‐up controlled detritus channels, thereby subsidising predator biomass, and in turn strengthening top‐down control in parallel grazing channels. These results testify to a fundamental role of detritus channels specifically and multi‐channel processes in general in mediating food web response to productivity and demonstrate that the ATCH provides an alternative explanation for classical predictions of top‐down control.