Abstract
As a consequence of global warming, it is important to characterise the potential changes occurring for some functional processes through the intra-specific study of key species. Changes in species distribution, particularly when key or engineer species are affected, should contribute to global changes in ecosystem functioning. In this study, we examined the potential consequences induced by global warming on ecosystem functioning in term of organic matter recycling. We compared consumption of leaf litter by some shredder populations (Gammarus pulex) between five tree species inhabiting continental (i.e., the northern region of the Rhône River Valley) and/or Mediterranean (i.e., the southern region of the Rhône River Valley) conditions. To consider any potential adaptation of the gammarid population to vegetation in the same climate conditions, three populations of the key shredder Gammarus pulex from the northern region and three from the southern region of the Rhône River Valley were used. We experimentally compared the effects of the geographical origin of both the gammarid populations and the leaf litter species on the shredding activity and the physiological state of animals (through body triglyceride content). This study demonstrated that leaf toughness is more important than geographical origin for determining shredder leaf litter consumption. The overall consumption rate of the gammarid populations from the southern region of Rhône Valley was much higher than that of the populations from the northern region, but no clear differences between the origins of the leaf litter (i.e., continental vs. Mediterranean) were observed. The northwards shift of G. pulex populations adapted to warmer conditions might significantly modify organic matter recycling in continental streams. As gammarid populations can demonstrate local adaptations to certain leaf species as a trophic resource, changes in riparian vegetation associated with climate change might locally affect the leaf litter degradation process by this shredder.
Highlights
Aquatic fauna will have to deal with increasing temperatures [1], [2], [3], ranging from +2uC to +6uC for atmospheric temperatures [4] which are strongly correlated with water temperatures
Few studies have focused on the consequences of climate change on different populations of the same species [16], [17], whereas the potential adaptation of populations inhabiting the margin of the distribution area, of species with a wide distributional area, might greatly modify the response at the species level [7], [18]
We proposed the following hypotheses: (i) the Mediterranean leaf litter species adapted to dry environmental conditions [30], is harder to consume than northern leaf litter species [31], [32], [33]; (ii) as southern populations of G. pulex are exposed to tougher leaves in their natural environment, these species should adapt to consume harder leaves and consume more southern leaves than the northern populations of G. pulex; and (iii) the amount of food consumed is not necessarily associated with the efficiency of energy storage in animals [34], [35], because leaves of different species might vary in nutritional quality [32], [36], [37]
Summary
Aquatic fauna will have to deal with increasing temperatures [1], [2], [3], ranging from +2uC to +6uC for atmospheric temperatures [4] which are strongly correlated with water temperatures. The environmental temperature influences latitudinal species distribution patterns and species replacements [6], [7], [8]. This shift, when key or engineer species are affected, contributes to global changes in ecosystem functioning [9]. Few studies have focused on the consequences of climate change on different populations of the same species [16], [17], whereas the potential adaptation of populations inhabiting the margin of the distribution area, of species with a wide distributional area, might greatly modify the response at the species level [7], [18]. For widely distributed species, characterising changes at the intra-specific level could be crucial to highlight the potential effects of climate changes
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