Figure 1. Responses of key biotic interactions to each global environmental change (GEC) driver. The figure presents the results of a synthesis of 688 separate published studies (Table S1) that have each examined the effect of at least one GEC driver on at least one interaction type (Figs S1–S5), totalling over 1000 specific species interactions. The number of specific pairwise interactions (or entire communities, when interactions were measured at the community scale) showing a decrease, increase, or no effect in the strength or frequency of the interaction, under that specific global change driver was recorded, and this number of interactions was the basis for quantifying changes to interaction frequencies in Fig. 1 and Figs S1–S6. This essentially gave extra weighting to studies that examined a greater variety of pairs of interacting species. Arrows with solid outlines indicate nutrient and energy flow, while double-headed arrows with dotted outlines indicate resource competition. + and − symbols within arrows indicate benefit or cost to each participant (e.g. + + within an arrow is a mutualism). The proportion of colours within each arrow indicates the proportion of published pairwise interactions of a given type affected by each of the GEC drivers present in our database (Table S1) showing increases (green), no effect (white), or decreases (dark grey), respectively, in the strength or frequency of the interaction following each of five major GEC drivers. Yellow arrows indicate a change in dominance between competing species. Width of arrows represents the number of studies considered in this review for each individual driver (small: ≤ 10; medium: 11–40; large: > 40 cases) and all drivers in combination (bottom right, small: ≤ 40; medium: 41–100; large: > 100 cases). In the Biotic Invasion panel, invasive species are depicted within circles, and the new interactions between invasive and native biota are depicted as an interaction (block arrow) with increasing strength. A table of the studies on which these trends are based (Table S1) is provided in the supporting information, with details regarding specific treatments and response variables. The final (bottom right) panel represents the summation of the individual effects of each driver (i.e. the number of pairwise interactions showing an increase, decrease, or no effect when studies of all GEC drivers are combined). Although we acknowledge that this ‘vote-counting’ approach can only give general indications of trends in the literature, it has been argued that a quantitative meta-analysis of such a large number of different response variables and specific treatments would give a false sense of confidence in the trends (see Ives & Carpenter 2007). We therefore emphasize that these are broad generalizations based on current literature, rather than predictions for any single system. Roman numerals describe the interactions as follows: (i) Plant–pollinator, (ii) Plant–fungal mutualism, (iii) Plant–seed disperser, (iv) Plant–plant competition, (v) Plant–hemiparasite, (vi) Plant–herbivore, (vii) Plant–pathogen, (viii) Plant–seed predator, (ix) Host–pathogen, (x) Animal–animal competition, (xi) Predator–prey, (xii) Soil food web. Enlargements are presented in the Figs S1–S6.
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