Spatial foraging segregation by close neighbours in a wide-ranging seabird.

Breeding seabirds are central-place foragers and therefore exploit food resources most intensively nearer their colonies. When nesting aggregations are close to one another density-dependent competition is likely to be high, potentially promoting foraging segregation (i.e. neighbouring colonies may segregate to search for food in different areas). However, little is known about spatial segregation in foraging behaviour between closely adjacent colonies, particularly in species that are wide-ranging foragers. Here, we tested for foraging segregation between two sub-colonies of a wide-ranging seabird, Cory's shearwater Calonectris borealis, separated by only 2 km, on a small Island in the North Atlantic. During the 2010 chick-rearing period, 43 breeding adults of both sexes were simultaneously sampled at both sub-colonies. A GPS logger was deployed on each individual and removed after several foraging trips at sea. Blood samples (plasma and red blood cells) were collected from each tracked individual for stable isotope analysis. Results indicated partial spatial segregation between the two sub-colonies during local foraging trips (i.e. those of ≤1 day duration and 216 km from the colony) accounting for 84.2% of all trips recorded. The location of the breeding sub-colony influenced the direction of travel of birds during local trips resulting in sub-colony-specific foraging areas. Although the oceanographic conditions associated with the foraging range of the two sub-colonies differed, no differences were found in the habitat exploited and in their estimated diets. This suggests that birds concentrated their feeding activity in patches of similar habitat and prey during the chick-rearing period.

Quantifying and addressing the prevalence and bias of study designs in the environmental and social sciences.

Building trust in science and evidence-based decision-making depends heavily on the credibility of studies and their findings. Researchers employ many different study designs that vary in their risk of bias to evaluate the true effect of interventions or impacts. Here, we empirically quantify, on a large scale, the prevalence of different study designs and the magnitude of bias in their estimates. Randomised designs and controlled observational designs with pre-intervention sampling were used by just 23% of intervention studies in biodiversity conservation, and 36% of intervention studies in social science. We demonstrate, through pairwise within-study comparisons across 49 environmental datasets, that these types of designs usually give less biased estimates than simpler observational designs. We propose a model-based approach to combine study estimates that may suffer from different levels of study design bias, discuss the implications for evidence synthesis, and how to facilitate the use of more credible study designs.

Effects of alien plants on insect abundance and biomass: a food-web approach.

The replacement of native plants by alien species is likely to affect other trophic levels, particularly phytophagous insects. Nevertheless, the effect of alien plants on insect biomass has not yet been quantified. Given their critical role in transferring energy from plants to higher trophic levels, if alien plants do affect insect biomass, this could have far-reaching consequences for community structure. We used 35 food webs to evaluate the impacts of alien plants on insect productivity in a native forest in the Azores. Our food webs quantified plants, insect herbivores, and their parasitoids, which allowed us to test the effects of alien plants on species richness and evenness, insect abundance, insect biomass, and food-web structure. Species richness of plants and insects, along with plant species evenness, declined as the level of plant invasion increased. Nevertheless, none of the 4 quantitative food-web descriptors (number of links, link density, connectance, and interaction evenness) varied significantly with plant invasion independent of the size of the food web. Overall, insect abundance was not significantly affected by alien plants, but insect biomass was significantly reduced. This effect was due to the replacement of large insects on native plants with small insects on alien plants. Furthermore, the impact of alien plants was sufficiently severe to invert the otherwise expected pattern of species-richness decline with increased elevation. We predict a decrease in insect productivity by over 67% if conservation efforts fail to halt the invasion of alien plants in the Azores.