Species interactions

Species interact in numerous ways, from competition and predation to mutualism and facilitation, many of them fundamental to the processes driving phenotypic evolution, structuring ecological communities and determining the composition and functioning of ecosystems altered by anthropogenic change. The role of interactions in limiting population size or driving microevolution (adaptation) can be demonstrated experimentally in the field or lab, and these effects are often proposed to explain broader-scale patterns in macroevolution (i.e. speciation or phenotypic variation above species level) and macroecology (i.e. the structure and distribution of biodiversity). However, the processes giving rise to these macro-scale patterns occur over millions of years and, as they cannot be witnessed during a human lifespan or even inferred from current traits and local communities, we still know remarkably little about the broader implications of species interactions.

We are addressing this problem using molecular phylogenies as temporal frameworks, since the amount of time or evolutionary change since lineages shared a common ancestor can be estimated from branch lengths of phylogenetic trees. This research programme requires large samples of species with well-resolved phylogenetic relationships, a suite of traits providing clear insight into function, and accurate data on occurrence, both globally and across local gradient or plot-based studies.

Our long-term field studies have revealed that ecological similarity is not limiting in mega-diverse environments such as rainforests. These studies also show how acoustic signals mediate interspecific competition, and how interspecific interactions can drive signal convergence through the process of agonistic character displacement. Meanwhile, experimentation on captive birds reveals that interspecific convergence in male signals can be accommodated by fine-tuning of perceptual abilities in female receivers. To address the question of how members of diverse assemblages partition signalling space, we study the timing and design of acoustic signals used by members of the Amazonian dawn chorus. We have been further testing these ideas using comparative analyses focusing on the passerine clade (>5000 species).

Major questions include: What are the relative influences of species interactions, divergence in environmental niche (e.g. climate, habitat) and life history (e.g. dispersal, sexual selection) on phenotypic evolution? How do species interactions shape complex communication networks? To what extent do species interactions limit co-occurrence? This latter possibility is a hot topic, partly because of the implications for predicting range shifts or extinctions in response to anthropogenic change. We have already clarified ecological constraints on co-occurrence in one bird family (Furnariidae), and the next step is to provide a quantitative framework for all birds, based on phylogenetic relationships and trait data, for estimating the likelihood of range overlap when predicting future shifts in range.