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Figure 1 | BMC Ecology

Figure 1

From: Troublesome toxins: time to re-think plant-herbivore interactions in vertebrate ecology

Figure 1

Dynamics of two-species plant communities subjected to a population of herbivores that feed optimally. N1 and N2 refer to biomasses of edible plants. The functional response used to generate the plots is the one shown in equation (1) of the text, modified to permit two plant species [48]. When toxins are not incorporated into the functional response (panel A), the plant species coexist. Note that herbivores feed exclusively on plant species 1 initially, i.e., σ1 = 1, σ2 = 0 (panel C), since the starting density of species 1 is higher. Once the density of species 2 exceeds that of species 1, the consumption constants switch to σ1 = 0, σ2 = 1, and the switches continue to occur (the switches occur so rapidly that it appears as a black area in panel C). When toxins are incorporated into the functional response and the resident plant species (species 1 in panel B) is more toxic than a prospective invading species (species 2 in panel B), simulation results demonstrate that the less toxic plant fails to establish. The failure is tied to the adaptive foraging behavior of the herbivore, resulting in a disproportionate fraction of its effort being expended on the less abundant (but less toxic) species 2 (panel D). Parameter values: c12 = 0.9, c21 = 0.9, r1 = r2 = 0.007, K1 = K2 = 7*105, B1 = B2 = 3.4*10-5, e1 = e2 = 0.0007, h1 = h2 = 0.008, mp = 0.0013. For simulations of plants containing toxins (panels B and D): G1 = 35, G2 = 60, initial density of species 1 = 5 × 105, initial density of species 2 = 5 × 103.

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