Temperature effects on long-term population dynamics in a parasitoid-host system

Long-term environmental changes will likely alter the strengths of interactions between species and consequently their population dynamics, leading to changes in the stability of ecological systems. While an increasing number of empirical studies have shown that environmental changes can alter the strengths of species interactions, these studies are typically short (<1–2 generations) and therefore give only partial information about longer term population dynamics. To focus on longer term dynamics, we investigated population cycles of pea aphids and their most common parasitoid, Aphidius ervi, in Wisconsin, USA. Data collected over three years in alfalfa fields showed an apparent host–parasitoid population cycle. Furthermore, higher pea aphid population growth rates and increased parasitism were correlated with higher naturally occurring temperatures. While these effects were observed with seasonal fluctuations in temperature, they beg the question of how long-term changes in mean an...