Impacts of deforestation‐induced warming on the metabolism, growth and trophic interactions of an afrotropical stream fish

Abstract

In ectotherms, anthropogenic warming often increases energy requirements for metabolism, which can either impair growth (when resources are limiting) or lead to higher predator feeding rates and possibly stronger top–down trophic interactions. However, the relative importance of these effects in nature remains unclear because: (1) thermal adaptation or acclimation could lower metabolic costs; (2) greater prey production at warmer temperatures could compensate for higher predator feeding rates; and/or (3) temperature effects on trophic interactions via altered biological rates could be small relative to other, temperature‐unrelated human impacts on food webs. Here, we examined effects of deforestation‐associated warming on the minnow Enteromius neumayeri, occurring in both forested (cool) and deforested (warm) streams located inside or nearby an afrotropical rainforest. Combining approaches from physiological and community ecology, we quantified impacts of anthropogenic warming on the metabolism, growth and trophic interactions of this tropical ectotherm. We then compared these effects with impacts of land use unrelated to temperature. In a long‐term laboratory acclimation experiment quantifying the temperature dependence of growth and metabolism in E. neumayeri, warming increased metabolic rates and decreased growth (at a limited ration). We found no evidence of local (thermal) adaptation, with warming affecting farm and forest populations similarly. Then, using mark–recapture methods to quantify impacts of warming on performance in situ, we found similar growth rates in fish from deforested and forested streams despite their distinct thermal environments. This suggests higher prey consumption at deforested sites to compensate for greater metabolic costs, which could strengthen fish–invertebrate interactions. Finally, we developed a bioenergetics model to estimate fish–invertebrate interaction strength and quantify temperature‐related and unrelated impacts of land use on this interaction. We found that although warming increased fish consumption, it apparently increased invertebrate production even more and thus had a net‐weakening effect on estimated interaction strength. Most importantly, variation in both fish and invertebrate density not directly related to temperature had a much stronger influence on estimated interaction strength than temperature effects on predator consumption and prey growth. We conclude that ectotherms can sometimes offset the metabolic costs of warming with a small increase in consumption that hardly effects food web interactions compared to non‐metabolic impacts of anthropogenic disturbances. Future research should assess whether this is a common feature of heavily impacted ecosystems facing multiple stressors. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13065/suppinfo is available for this article.

Low diversity of fishes in high elevation Afrotromontane streams renders them unsuitable for biomonitoring

“…Small‐bodied Enteromius and Clarias spp. are rhithronic species with preferences for cover and limnophilic features (Fugère, Mehner, et al, 2018; Harniman et al, 2013; Muñoz‐Mas et al, 2019). The longitudinal distribution of fishes in the Sondu‐Miriu River is also influenced by the Odino Waterfalls, which prevent the upstream migration of fishes.…”

“…Small-bodied Enteromius and Clarias spp. are rhithronic species with preferences for cover and limnophilic features (Fugère, Mehner, et al, 2018;Harniman et al, 2013;Muñoz-Mas et al, 2019).…”

Model‐based decomposition of environmental, spatial and species‐interaction effects on the community structure of common fish species in 772 European lakes

“…In contrast to the temperature–size rule, the average size of two cyprinids (bream, Abramis brama , and rudd, Scardinius erythrophthalmus ) was higher in warmer lakes. This is certainly attributable to the higher productivity of the warmer (and often shallow) lakes, suggesting that the higher maintenance costs at higher temperatures affect the growth rates negatively only in conditions of resource limitation and strong intra‐ and interspecific competition (Bourai et al, 2020; Fugère et al., 2018). In contrast, the size of the predator species pike declined with higher temperatures, suggesting that pike cannot cover the higher energetic costs induced by increasing temperatures by higher prey uptake rates; for example, if some of their prey species, such as bream and rudd, escape into a size refuge by higher growth rates (Mehner et al., 2016).…”

Ecosystem response to earlier ice break‐up date: Climate‐driven changes to water temperature, lake‐habitat‐specific production, and trout habitat and resource use

“…Increased climate variation (Dai, 2013; Min, Zhang, Zwiers, & Hegerl, 2011) is likely to drive complex effects on ecosystem and habitat production, with unclear results for consumers and their habitat or resource use (Rosenblatt & Schmitz, 2016). Studies that incorporate climate‐driven changes to habitat‐specific productivity and environmental conditions, coupled with measured responses of individuals, communities and populations are needed to understand and forecast ecosystem level consequences of climate warming (but see Fugère, Mehner, & Chapman, 2018; Stoner et al., 2018).…”