PS 6-49
Differential responses of two ecologically similar species to variation in temperature and resources
How species respond to shifting environmental conditions is a central question in ecology, especially because ecosystems are currently experiencing rapidly changing climatic conditions. However, predicting how species interactions and community composition might respond to changing conditions is often difficult. Species with complex life cycles, such as dragonflies, are especially interesting systems in which to examine potential effects of changing environmental conditions. For such species, the influence of rearing conditions may result in carry-over effects into adult life stages. We examined the effects of rearing temperature and resource level on larval survival of two ecologically similar species of dragonflies, Erythemis collocata (western pondhawk) and Pachydiplax longipennis (blue dasher). Within high (26 degrees Celsius) and low (21 degrees Celsius) temperatures, we crossed species and resource level and reared larvae individually. We predicted that individuals in the warmer tanks would exhibit a lower survival rate and that higher resource availability should positively influence survival. Because these two ecologically similar species share a similar distribution in the western United States, we expected the two species to respond similarly to experimental conditions.
Results/Conclusions
We found that temperature affected survival, with lower survival rates in tanks at the higher temperature. There was also an interaction between temperature and species; western pondhawk survival was more responsive to temperature than was blue dasher survival. Resource level did not appear to affect survival in either species. These results suggest that these two species might not respond similarly to changing environmental conditions. Thus, global climate change might be expected to affect interactions between these two sympatric, ecologically similar species, with potential consequences for community composition.