Climate change exacerbates interspecific interactions in sympatric coastal fishes

Abstract

Summary1. Biological responses to warming are presently based on the assumption that species will remain within their bioclimatic envelope as environmental conditions change. As a result, changes in the relative abundance of several marine species have been documented over the last decades. This suggests that warming may drive novel interspecific interactions to occur (i.e. invasive vs. native species) or may intensify the strength of pre-existing ones (i.e. warm vs. cold adapted). For mobile species, habitat relocation is a viable solution to track tolerable conditions and reduce competitive costs, resulting in 'winner' species dominating the best quality habitat at the expense of 'loser' species. 2. Here, we focus on the importance of warming in exacerbating interspecific interactions between two sympatric fishes. We assessed the relocation response of the cool-water fish Coris julis (a potential 'loser' species in warming scenarios) at increasing relative dominance of the warm-water fish Thalassoma pavo (a 'winner' species). These wrasses are widespread in the Mediterranean nearshore waters. C. julis tolerates cooler waters and is found throughout the basin. T. pavo is common along southern coasts, although the species range is expanding northwards as the Mediterranean warms. 3. We surveyed habitat patterns along a thermo-latitudinal gradient in the Western Mediterranean Sea and manipulated seawater temperature under two scenarios (present day vs. projected) in outdoor arenas. Our results show that the cool-water species relocates to a lesspreferred seagrass habitat and undergoes lower behavioural performance in warmer environments, provided the relative dominance of its warm-water antagonist is high. 4. The results suggest that expected warming will act synergistically with increased relative dominance of a warm-water species to cause a cool-water fish to relocate in a less-preferred habitat within the same thermal environment. 5. Our study highlights the complexity of climate change effects and has broad implications for predictive models of responses to warming. To achieve more accurate predictions, further consideration is needed of the pervasive importance of species interactions. We believe these fundamental issues to be addressed to understand the biotic consequences of climate change.

Evidence for large-scale effects of competition: niche displacement in Canada lynx and bobcat

“…Habitat considered to be suitable in rspb.royalsocietypublishing.org Proc R Soc B 280: 20132495 the future could be limited based on pressure from competitors or predators [43,44]. Furthermore, population declines or increases owing to changing habitat suitability could be accelerated in the presence of competition and predation [45,46]. Our results also suggest a less obvious effect of biotic interactions, whereby competition alters range-wide speciesenvironment relationships; this type of effect will also alter future range shifts and distribution patterns of species.…”

Life history trade-offs, the intensity of competition, and coexistence in novel and evolving communities under climate change

“…While numerous studies have provided evidence of changing competitive interactions in response to climate change [10,21,22], it is more difficult to identify how climatic warming affects the overall importance of competition for shaping communities [23]. In general, changes in the intensity of interspecific competition under climate change are likely to be driven by several distinct, but sometimes synergistic, processes: first, changes in the extent and diversity of favourable habitats may alter patterns of competition for remaining space and resources [10,24 -27].…”

“…Potentially equally or more important to future community diversity are effects of warming on changes in the outcomes of competitive interactions, but these have received much less attention to date. Like trophic interactions, competitive interactions may intensify or diminish under climate change [9,10], with important consequences for local biodiversity and ecosystem services.…”

Temporal partitioning of diurnal behavioural patterns of Coris julis and Diplodus vulgaris (Actinopterygii: Perciformes) in Mediterranean coralligenous habitats

“…Defi nitions of the categories of main individual activities are defi ned based on the work of Fulton and Bellwood (2002) and Milazzo et al (2013).…”

“…The observer was trained to estimate individual sizes with a database of screenshots of plastic fi sh silhouettes of different colours (bright and dark ones), known sizes (0.2 m, 0.4 m, 0.6 m, 0.8 m, and 1 m) and known distances from the same camera (2 m, 5 m, 7 m, and 10 m) (Mallet et al 2014). In addition, the behaviour of each individual of C. julis and D. vulgaris was analysed according to the behavioural categories defi ned in Table 2, based on defi nitions of quantifi cation of fi sh behaviour in Fulton and Bellwood (2002) and Milazzo et al (2013).…”