Does like replace like? Local adaptation and phenotypic plasticity in the macrophysiology of food chain interactions

Background/Question/Methods: Concern abounds about the inability of species to adapt to a changing climate, which may have important implications for ecological functioning. Evolutionary theory, however, suggests that species could be resilient either through phenotypic plasticity or local adaptation. Thus, species populations may tolerate climate change through physiological acclimation (plasticity) or by the replacement of thermally intolerant populations with thermally tolerant ones (migration of locally adapted populations). Further, it remains unclear whether populations with different thermal sensitivities also differ in their functional roles within communities. We conducted a reciprocal transplant experiment in two consecutive years (2013 and 2014) to test for evidence of phenotypic plasticity in the physiological thermal sensitivity of two Melanoplus femurrubrum grasshopper populations: one in northeastern Connecticut (CT) and one 300 km north in northern Vermont (VT), USA. During summer, the Vermont site was on average 3ºC cooler with 1.5X greater temperature variation than the Connecticut site. We measured how thermal sensitivity (thermal Q₁₀ effect) translated into grasshopper survival (fitness component) and the strength and nature of grasshopper impact on the plant community (grasses and goldenrod). 

Results/Conclusions: Both populations exhibited phenotypically plastic changes in Q_10.  But, Q₁₀ in Vermont was 1.5X broader for both populations than in Connecticut because populations in Connecticut elevated their metabolism at the cooler temperature. All populations at all sites had similar survivorship, indicating adaptive plasticity. This did not, however, translate into similar population effects on the plant community. Each grasshopper population had stronger effects on grasses in their home field sites than in their transplanted sites. Only VT grasshoppers at the Connecticut transplant site had significant effects on goldenrod. Our findings show that species could physiologically acclimate quickly under new thermal conditions, suggesting stronger tolerance to change than often presumed. Nevertheless, thermal acclimatization may not translate into the maintenance of a species’ functional role.