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Ecosystem engineers modify habitats in ways that facilitate other community members by ameliorating harsh conditions. The strength of such facilitation is predicted to be influenced by both beneficiary traits and abiotic context. One key trait of animals that could control the strength of facilitation is beneficiary body size because it should determine how beneficiaries fit within and exploit stress ameliorating habitat modifications. However, few studies have measured how beneficiary body size relates to facilitation strength along environmental gradients.We examined how the strength of facilitation by net‐spinning caddisflies on invertebrate communities in streams varied along an elevation gradient and based on traits of the invertebrate beneficiaries. We measured whether use of silk retreats as habitat concentrated invertebrate density and biomass compared to surrounding rock surface habitat and whether the use of retreat habitat varied across body sizes of community members along the gradient.We found that retreats substantially concentrated the densities of a diversity of taxa including eight different Orders, and this effect was greatest at high elevations. Caddisfly retreats also concentrated invertebrate biomass more as elevation increased. Body size of invertebrates inhabiting retreats was lower than that of surrounding rock habitats at low elevation sites, however, body size between retreats and rocks converged at higher elevation sites. Additionally, the body size of invertebrates found in retreats varied within and across taxa. Specifically, caddisfly retreats functioned as a potential nursery for taxa with large maximal body sizes. However, the patterns of this taxon‐specific nursery effect were not influenced by elevation unlike the patterns observed based on community‐level body size.Collectively, our results indicate that invertebrates use retreats in earlier life stages or when they are smaller in body size independent of life stage. Furthermore, our analysis suggests that facilitation strength intensifies as elevation increases within stream invertebrate communities.Further consideration of how trait variation and environmental gradients interact to determine the strength and direction of biotic interactions will be important as species ranges and environmental conditions continue to shift. [ABSTRACT FROM AUTHOR]

Theory suggests that non‐trophic interactions can be a major mechanism behind community stability and persistence, but community‐level empirical data are scarce, particularly for effects on species interactions mediated through changes in the physical environment.Here, we explored how ecosystem engineering effects can feed back to the engineer, not only modulating the engineer's population density (node modulation) but also affecting its interactions with other species (link modulation).Gall induction can be viewed as ecosystem engineering since galls serve as habitat for other species. In a community‐level field experiment, we generated treatments with reduced or elevated ecosystem engineering by removing or adding post‐emergence galls to different plots of their host plant in the Brazilian Cerrado. We tested the effect of post‐emergence galls on the galler, as well as on the galler–parasitoid and galler—aphid interactions.The manipulation of post‐emergence galls had little effect on the galler—abundance and survivorship were not affected, and gall volume changed only slightly—but modified interactions involving the galler, parasitoid wasps and inquiline aphids. Aphid inquilines negatively affected density‐dependent parasitism rates (interaction modification) likely by killing parasitised galling larvae. Post‐emergence galls interfered with aphid inquilinism—likely by the provision of alternative habitat for aphids—and thus interfered with the negative effect of aphids on parasitism (modification of an interaction modification).This work is one of the few studies to demonstrate experimentally the role played by environment‐mediated interaction modification at a community level in the field. Moreover, by manipulating a species' ecosystem engineering effect (post‐emergence galls) instead of the species itself, we demonstrate the novel result that populations can be regulated by non‐trophic effects initiated by their own activities that alter their interaction with other species. This reveals that indirect interactions mediated via the environment offer new pathways of feedback loops for population regulation. Our results indicate that interaction modification has the potential to be a key regulatory mechanism underlying interaction variation in nature, and play a major role in community structure, dynamics and stability. [ABSTRACT FROM AUTHOR]

Large mammalian herbivores ( LMH) strongly shape the composition and architecture of plant communities. A growing literature shows that negative direct effects of LMH on vegetation frequently propagate to suppress the abundance of smaller consumers. Indirect effects of LMH on the behaviour of these consumers, however, have received comparatively little attention despite their potential ecological significance., We sought to understand (i) how LMH indirectly shape small-mammal habitat use by altering the density and distribution of understorey plants; (ii) how these effects vary with climatic context (here, seasonality in rainfall); and (iii) the extent to which behavioural responses of small mammals are contingent upon small-mammal density., We tested the effects of a diverse LMH community on small-mammal habitat use using 4 years of spatially explicit small-mammal trapping and vegetation data from the UHURU Experiment, a replicated set of LMH exclosures in semi-arid Kenyan savanna., Small-mammal habitat use was positively associated with tree density and negatively associated with bare (unvegetated) patches in all plots and seasons. In the presence of LMH, and especially during the dry season, small mammals consistently selected tree cover and avoided bare patches. In contrast, when LMH were excluded, small mammals were weakly associated with tree cover and did not avoid bare patches as strongly. These behavioural responses of small mammals were largely unaffected by changes in small-mammal density associated with LMH exclusion., Our results show that LMH indirectly affect small-mammal behaviour, and that these effects are influenced by climate and can arise via density-independent mechanisms. This raises the possibility that anthropogenic LMH declines might interact with changing patterns of rainfall to alter small-mammal distribution and behaviour, independent of numerical responses by small mammals to these perturbations. For example, increased rainfall in East Africa (as predicted in many recent climate-model simulations) may relax constraints on small-mammal distribution where LMH are rare or absent, whereas increased aridity and/or drought frequency may tighten them. [ABSTRACT FROM AUTHOR]

The effects of mammalian ecosystem engineers on soil microbial communities and ecosystem functions in terrestrial ecosystems are poorly known. Disturbance from livestock has been widely reported to reduce soil function, but disturbance by animals that forage in the soil may partially offset these negative effects of livestock, directly and/or indirectly by shifting the composition and diversity of soil microbial communities. Understanding the role of disturbance from livestock and ecosystem engineers in driving soil microbes and functions is essential for formulating sustainable ecosystem management and conservation policies. We compared soil bacterial community composition and enzyme concentrations within four microsites: foraging pits of two vertebrates, the indigenous short-beaked echidna (Tachyglossus aculeatus) and the exotic European rabbit (Oryctolagus cuniculus), and surface and subsurface soils along a gradient in grazing-induced disturbance in an arid woodland. Microbial community composition varied little across the disturbance gradient, but there were substantial differences among the four microsites. Echidna pits supported a lower relative abundance of Acidobacteria and Cyanobacteria, but a higher relative abundance of Proteobacteria than rabbit pits and surface microsites. Moreover, these microsite differences varied with disturbance. Rabbit pits had a similar profile to the subsoil or the surface soils under moderate and high, but not low disturbance. Overall, echidna foraging pits had the greatest positive effect on function, assessed as mean enzyme concentrations, but rabbits had the least. The positive effects of echidna foraging on function were indirectly driven via microbial community composition. In particular, increasing activity was positively associated with increasing relative abundance of Proteobacteria, but decreasing Acidobacteria. Our study suggests that soil disturbance by animals may offset, to some degree, the oftreported negative effects of grazing-induced disturbance on soil function. Further, our results suggest that most of this effect will be derived from echidnas, with little positive effects due to rabbits. Activities that enhance the habitat for echidnas or reduce rabbit populations are likely to have a positive effect on soil function in these systems. [ABSTRACT FROM AUTHOR]

Migration and re-colonization enable organisms to persist in metapopulations. Re-colonization success may be limited by the number of arriving migrants or by patch quality. In a well-studied rock pool Daphnia metapopulation, it is frequently assumed that re-colonization is limited by the number of arriving migrants, and that all patches are equally suitable for colonization. This assumption strongly influences how observations about dynamics, epidemiology and population genetics for the entire metapopulation are interpreted. Here we test this assumption., In 627 rock pools, we found that high pH, high Ca++ and high water conductivity were positively correlated with the presence of D. magna. The experimental release of D. magna into randomly chosen natural pools revealed the highest colonization success in pools with high pH. Next, we elevated pH and Ca++ concentrations in natural pools by adding a system-specific natural source of calcium carbonate (either from crushed oyster shells or from eider duck droppings, which contain blue mussel shells). These treatments led to a rapid increase in pH and Ca++ and strongly raised the likelihood that introduced D. magna would establish persistent populations. Therefore, we conclude that low pH and Ca++ result in unsuitable colonization conditions in two-thirds of the untreated pools., A further experiment revealed that natural colonization rates were about five times higher in calcium-treated pools than in untreated pools. Finally, we observed that eider droppings are more frequently found in the catchment area of occupied pools, than they are in those of unoccupied pools, suggesting that the blue mussel shells contained in the eider droppings play an important role in making pools suitable for colonization and in enabling D. magna to persist. Thus, eider ducks are ecosystem engineers in this system., We recalculate typical metapopulation parameters to account for the unsuitable pools, resulting in a much more dynamic picture of this metapopulation than previously believed, with colonization rates and gene flow three to five times higher. These results have strong implications for metapopulation persistence, local and global genetic diversity, genetic rescue, gene flow and local adaptation. Our results emphasize that without verifying patch suitability, estimated rates of metapopulation dynamics can severely underestimate the true rates. [ABSTRACT FROM AUTHOR]