Figure 1.
Markers indicate names and field site locations in Canterbury, South Island, New Zealand.
Table 1.
Coordinates for all field sites located on the South Island, New Zealand, including average site temperature (±SE) during the sampling period with rainfall and altitude data.
Figure 2.
Temperature effects on each trophic level.
Relationship between mean daily temperatures and (A) aphid abundance (Z = 0.18, P = 0.857), (B) proportion of aphids parasitised (Z = 5.91, P<0.001), and (C) proportion of aphids hyperparasitised (Z = 1.71, P = 0.087). Dashed lines indicate non-significant effects. Note: data are site averages, whereas individual measurement dates were analysed, grouped by sites, in the mixed effects models.
Table 2.
Results for GLMMs for all field data on the relationships between temperature and aphid population growth and parasitism.
Figure 3.
Interactive effects of temperature and drought on aphid population growth.
Rate of aphid population growth in laboratory mesocosms under 3 treatments, calculated using aphid abundance in parasitoid (Diaeretiella rapae) treatments minus aphid abundances in the predator-free control to give the overall net predator effect (±SE). Temperature caused the greatest reduction in aphid population growth (Z = −4.87, P<0.001) followed by drought (Z = −5.92, P<0.001). In contrast, in the drought × temperature treatment (Z = 11.29, P<0.001) treatment, aphid population growth was positive.
Figure 4.
Effects of temperature and drought on parasitoid fitness.
(A) Parasitoid longevity under drought, elevated temperature, drought and elevated temperature, and control treatments (±SE). (B) Number of offspring per female (dark bars) and percentage of successful adult emergence (light bars) (*temperature: Z = 2.29, P = 0.02, **drought × temperature: Z = −3.26, P = 0.001).
Table 3.
Results for all laboratory experiments on the effects of elevated temperature, drought, and their interaction, on parasitoid life-history parameters and aphid population response to parasitism using GLMMs, GLMs, and two-way ANOVAs.