Projecting future response of biological systems to global change requires a mechanistic understanding of how climate and ecology jointly drive species demography and range dynamics. Such knowledge is particularly crucial when it comes to invasive species, which expansion may have far-reaching consequences for recipient ecosystems. Here, we use mark-recapture in replicated outdoor mesocosms to examine how survival and dispersal, two key drivers of population and range dynamics, respond to climate and ecology in the invasive red swamp crayfish (Procambarus clarkii) along an invasion gradient. We show that crayfish survival probability increased with (i) increasing body size at high (but not low) crayfish density and (ii) with warmer temperatures, and decreased (i) with increasing body condition and (ii) under higher crayfish density. Overland dispersal probability by crayfish increased with increasing (i) body-size, (ii) body condition and (iii) temperatures. In contrast, crayfish from range-edge and range-core habitats had similar survival and overland dispersal probabilities, suggesting no evolution of the crayfish expansion potential along the invasion gradient. Our results highlight that species population dynamics and range shifts in a changing world are driven by joint contributions from both climate and ecology. In P. clarkii, global warming will simultaneously promote both a demographic increase and a geographic range expansion, especially in populations dominated by large-bodied individuals.
Structurally-complex habitats harbour more taxonomically-diverse and more productive communities, a phenomenon generally ascribed to habitat complexity relaxing the strength of interspecific predation and competition. Here, we challenge this classical, community-centred view by showing that positive habitat complexity-productivity relationships may also emerge from between-age-class, intra-specific interactions at a single-population level. In replicated outdoor pond populations of the medaka fish (Oryzias latipes), structurally complex habitats provide refuges to newborns and relax the strength of cannibalism, resulting in increased survival of age-0+ individuals, in a 80 % increase in population growth rate, and in dampened negative density-dependence indicating elevated habitat carrying capacity. The resultant higher population density in complex habitats was associated with increased competition for food among age-0+ and age-1+ individuals, as revealed by their smaller and more variable body sizes. Positive habitat complexity-productivity relationships may thus be considered as a generally-emergent property of both size-structured communities and populations, in which a larger body size brings a predation advantage. Our results highlight that anthropogenic habitat simplification drives biodiversity loss not only from community- but also from population-level processes, and hence may further reduce population productivity in the surviving species. Enhancement of habitat structural complexity is therefore a pivotal action for biodiversity improvement, not only in the context of ecosystem management, but also for successful conservation of endangered populations.
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