Figure 1.
Sites (black dots) were 150×150 m in size and were randomly selected from a 360 km2 landscape (black circle) in Johnson County, IA, USA. All sites were inventoried for presence and abundance of black walnut and black cherry trees and their respective fruit flies and parasitoids (see methods). Landscape areas shown include urban/suburban development (gray), agricultural land (yellow), “natural” wooded and herbaceous areas (green), and water (blue).
Table 1.
Coarse- and fine-grain landscape categories used in this study.
Table 2.
Summary statistics for host trees and insects sampled.
Figure 2.
Occupancy of sites by trees, flies and parasitoid wasps at coarse and fine grain resolutions.
Letters in common indicate no significant difference via pairwise Fisher's exact test (p<0.05) within a trophic level. P-values are shown in Table S3. Category names are explained in Table 1 and sample sizes are shown in Table 2. For trees, proportions are in relation to the total number of sites in each landcover class. Only sites with fruits were used to calculate proportions of sites with flies. Similarly, only sites with flies were used to calculate proportions of sites with wasps. A. Proportions of sites occupied across coarse grain landcover categories, B. Proportions of sites occupied across fine grain landcover categories.
Figure 3.
Mean rank tree density and insects parasitism rates (± SE) compared between trophic levels.
Trees are symbolized with black circles, flies with gray circles, and wasps with white circles. Low mean ranks represent higher densities/parasitism rates and vice versa. Ranges of raw values corresponding to ranks are: walnut trees per site, 0-66; cherry trees per site, 0-180; walnut fly larvae per fruit, 0.250-75.500; cherry fly larvae per fruit, 0.000-0.401; walnut wasps per fly pupae, 0.000-0.312; cherry wasps per fly larvae, 0.000-0.212. P-values reflecting significance of differences across landcover within trophic levels are reported in Table S5.
Table 3.
Inter-trophic correlations across coarse grain landcover categories.
Figure 4.
Local spatial autocorrelation (SA) in parasitism rates for cherry and walnut flies.
Symbols indicate sites with positive (plus signs), negative (triangles), and no autocorrelation (dots). Symbols indicating centers of significant local autocorrelation (Moran's I, p<0.05) are shown in white, while all others are shown in black. Landscape areas presented include urban/suburban development (gray), agricultural land (yellow), “natural” wooded and herbaceous areas (green), and water (blue). More information regarding interpretation of this figure is provided in Appendix S3.
Table 4.
Linear regression models in which landcover best predicted fly and wasp parasitism rates.