Testing for effects of climate change on competitive relationships and coexistence between two bird species

Abstract

Climate change is expected to have profound ecological effects, yet shifts in competitive abilities among species are rarely studied in this context. Blue tits (Cyanistes caeruleus) and great tits (Parus major) compete for food and roosting sites, yet coexist across much of their range. Climate change might thus change the competitive relationships and coexistence between these two species. Analysing four of the highest-quality, long-term datasets available on these species across Europe, we extend the textbook example of coexistence between competing species to include the dynamic effects of long-term climate variation. Using threshold time-series statistical modelling, we demonstrate that long-term climate variation affects species demography through different influences on density-dependent and density-independent processes. The competitive interaction between blue tits and great tits has shifted in one of the studied sites, creating conditions that alter the relative equilibrium densities between the two species, potentially disrupting longterm coexistence. Our analyses show that long-term climate change can, but does not always, generate local differences in the equilibrium conditions of spatially structured species assemblages. We demonstrate how long-term data can be used to better understand whether (and how), for instance, climate change might change the relationships between coexisting species. However, the studied populations are rather robust against competitive exclusion.

Effects of interspecific coexistence on laying date and clutch size in two closely related species of hole‐nesting birds

“…The present study was based on nest boxes, and the population density of the number of occupied boxes per unit area does not apply to the fraction of the population breeding in natural holes. This situation does not differ from analyses of other nest box populations (e.g., Dhondt, ; Dhondt et al., ; Gustafsson, ; Minot, , ; Siriwardena et al., ; Stenseth et al., ; Török & Tóth, ).…”

“…Both great and blue tits have a large distribution, and, therefore, they are ideal for addressing questions about competition at large spatial and temporal scales. The large temporal and spatial variation in the resources subject to competition is a source of variance that can readily be implemented into the study of competition, but has only been so to a very limited and, so far, unplanned extent (Stenseth et al., ). We suggest that deliberate comparison between sympatric populations of congeners inhabiting spatially and temporally variable environments will allow for much more powerful statistical tests.…”

Distribution of a climate‐sensitive species at an interior range margin

“…Impacts of contemporary climate change on interspecific interactions remain an understudied research frontier (Stenseth et al. ).…”

Niche partitioning of sympatric penguins by leapfrog foraging appears to be resilient to climate change

“…The alteration of competitive interactions by climate change has received less attention, although a growing body evidence demonstrates that the presence of competitors may have substantial effects on the magnitude and form of a species’ response to climate change. Examples include barnacles (Poloczanska, Hawkins, Southward, & Burrows, ), insects (Bulgarella, Trewick, Minards, Jacobson, & Morgan‐Richards, ), fish (Helland, Finstad, Forseth, Hesthagen, & Ugedal, ; Milazzo, Mirto, Domenici, & Gristina, ) and birds (Sætre, Post, & Král, ; Stenseth et al., ). Ecologically similar species may alter their breeding phenology in response to warming at different rates (Chadwick, Slater, & Ormerod, ; Lynch, Fagan, Naveen, Trivelpiece, & Trivelpiece, ) and, where breeding cycles become more synchronised, increases in competitive interactions may arise (Ahola, Laaksonen, Eeva, & Lehikoinen, ), which we hereafter term as “competitor matching.”…”