Dietary guild composition and disaggregation of avian assemblages under climate change

Abstract

Climate change is expected to cause geographic redistributions of species. To the extent that species within assemblages have different niche requirements, assemblages may no longer remain intact and dis- and reassemble at current or new geographic locations. We explored how climate change projected by 2100 may transform the world's avian assemblages (characterized at a 110 km spatial grain) by modeling environmental niche-based changes to their dietary guild structure under 0, 500, and 2000 km-dispersal distances. We examined guild structure changes at coarse (primary, high-level, and mixed consumers) and fine (frugivores, nectarivores, insectivores, herbivores, granivores, scavengers, omnivores, and carnivores) ecological resolutions to determine whether or not geographic co-occurrence patterns among guilds were associated with the magnitude to which guilds are functionally resolved. Dietary guilds vary considerably in their global geographic prevalence, and under broad-scale niche-based redistribution of species, these are projected to change very heterogeneously. A nondispersal assumption results in the smallest projected changes to guild assemblages, but with significant losses for some regions and guilds, such as South American insectivores. Longer dispersal distances are projected to cause greater degrees of disassembly, and lead to greater homogenization of guild composition, especially in northern Asia and Africa. This arises because projected range gains and losses result in geographically heterogeneous patterns of guild compensation. Projected decreases especially of primary and mixed consumers most often are compensated by increases in high-level consumers, with increasing uncertainty about these outcomes as dispersal distance and degree of guild functional resolution increase. Further exploration into the consequences of these significant broad-scale ecological functional changes at the community or ecosystem level should be increasingly on the agenda for conservation science.

Functional biogeography of dietary strategies in birds

“…Diets influence demographic and distributional responses of species to modifications in land use through their determinant role on offspring productivity and other aspects of energetic demands (Newbold et al, ; Sibly et al, ). The outcomes of a dietary homogenization of bird assemblages associated with the human imprint would thus deserve a more mechanistic assessment, especially with respect to the persistence and resilience of critical bird functions, such as pollination, endozoochorous dispersal and pest control (Ko, Schmitz, Barbet‐Massin, & Jetz, ; Şekercioğlu, , ).…”

Expanding population edges: theories, traits, and trade‐offs

“…Populations that disperse faster than populations with which they have specific relationships will need to either change the relationship at the edge (by switching to a substitute species or losing the relationship entirely) or be limited by the slower disperser's speed. Ecological niche models of avian communities, for example, have projected a decrease in functional diversity (Barbet‐Massin & Jetz, ) and substantial changes in dietary guild composition (Ko et al ., ), with more severe changes occurring with higher dispersal rates. The degree to which trait shifts at range edges could affect these complex community dynamics remains mostly uninvestigated and is a promising avenue for future theoretical investigations.…”

What North America's skeleton crew of megafauna tells us about community disassembly

“…Impressive, global scale models use functional diversity to predict the effects of community disassembly on large taxonomic groups given expected climate change [11,12] but ground truthing these models is difficult. Despite decades of fruitful research on community assembly, we still have a poor understanding of community disassembly and how it relates to functional diversity [13].…”