Bird species co‐occurrence patterns in an alpine environment supports the stress‐gradient hypothesis

Abstract

Understanding the relative contribution of different biotic interactions in shaping species assemblages constitutes a major goal in community ecology, and consequently, multiple methods aimed at inferring the nature of these associations have emerged during the last decade. In this framework, the stress‐gradient hypothesis (SGH) predicts that prevalent biotic interactions shift from competition to facilitation as abiotic stress increases (and productivity decreases). This hypothesis originally raised by plant ecologists has been barely applied to faunal communities. Here, we take advantage of 20 years of abundance data to investigate pairwise patterns in species co‐occurrence in alpine bird communities inhabiting two contrasting habitat types: forests (high productivity) and mountain grasslands (low productivity). We also integrate functional data with presence–absence and quantitative matrices in order to detect the signature of processes driving community assembly and test for limiting similarity. We employ a null model approach, probabilistic pairwise association tests and joint species distribution models; all methods revealed a higher frequency of positive interactions in mountain grasslands in agreement with SGH predictions. Both the frequency of positive and negative interactions remained moderately stable over the study period in both habitat types. There was no significant relationship between the degree of co‐occurrence of species pairs and their functional distance in either habitat. However, when we only considered those combinations of species whose co‐occurrence patterns deviated from that expected at random, we found that co‐existing species are functionally more similar than those pairs that show segregated patterns in the forest assemblages. Such a relationship may arise via selective social information use and other processes, including microhabitat preferences. Overall, our findings suggest that interspecific competition does not constitute a major force driving the structure of bird assemblages in this mountain region. This work also shows that association analyses should not be underestimated as they can provide clues to the mechanisms responsible for community structure.

Ecological engineering across a spatial gradient: Sociable weaver colonies facilitate animal associations with increasing environmental harshness

“…This study provides empirical support for the SGH and complements recent research using terrestrial animal communities that found evidence of increased importance of associative or facilitative interactions in harsh environments (Bell & Cuddington, 2019;Dangles et al, 2018;García-Navas et al, 2021). Additionally, by demonstrating that some taxa associate strongly with colony trees in more arid climates, we provide support that facilitation by weaver colonies increases the realized niches of certain species (Armas et al, 2011;He & Bertness, 2014).…”

“…Additionally, by demonstrating that some taxa associate strongly with colony trees in more arid climates, we provide support that facilitation by weaver colonies increases the realized niches of certain species (Armas et al, 2011; He & Bertness, 2014). Furthermore, only one other study has extended this hypothesis to free‐ranging animals (García‐Navas et al, 2021), as many of the previous studies were tested under laboratory conditions (Bell & Cuddington, 2019; Dangles et al, 2018). Temporal variations in climatic conditions may also play a part in understanding the facilitative role of weaver colonies.…”

“…This is supported by empirical evidence demonstrating greater associative and positive between‐species impacts with increasing environmental stress, often facilitated by identified ecosystem engineers (He et al, 2013). To date, studies into the SGH have almost been exclusively tested in plant communities; however, recently, ecologists started to apply these ideas to animal communities (Dangles et al, 2018; García‐Navas et al, 2021; Lowney & Thomson, 2021). Moreover, studies across broad spatial scales are challenging to replicate but may demonstrate the importance of engineering species to different communities and in different contexts.…”

Human disturbance increases spatiotemporal associations among mountain forest terrestrial mammal species

“…Understanding how species associations vary along environmental conditions is pivotal in making robust ecological predictions about biodiversity responses to changing environmental conditions (Dangles et al, 2018;Perrin et al, 2022). For example, alpine bird communities have a higher frequency of positive interactions in grasslands with low productivity compared with in forests with high productivity (García-Navas et al, 2021).…”

Modularity in temporal co-occurrence networks at a stopover site reveals strong co-migration fidelity in African-European migratory landbirds over time

“…Within this context, co-occurrence analysis and co-occurrence networks are valuable tools to elucidate mechanisms driving species assemblages. Recently, García-Navas et al (2021) [35] used null model approaches on 20 years of abundance data to investigate co-occurrence patterns in bird communities inhabiting habitats with different degree of productivity, showing the role of social information and microhabitat preferences over interspecific competition. Furthermore, Montaño-Centellas (2020) [36] used spatial data to build and explore co-occurrence networks of avian mixed-species flocks across elevation gradients, identifying changes in interactions as the main driver of species turnover among Andean flocking birds.…”