Density regulation of co-occurring herbivores via two indirect effects mediated by biomass and non-specific induced plan
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ORIGINAL PAPER
Density regulation of co-occurring herbivores via two indirect effects mediated by biomass and non-specific induced plant defenses Atsushi Yamauchi 1
&
Yusuke Ikegawa 2 & Takayuki Ohgushi 1 & Toshiyuki Namba 3
Received: 13 March 2020 / Accepted: 18 August 2020 # Springer Nature B.V. 2020
Abstract Two herbivorous species that share a single plant can interact indirectly with one another, even without direct interaction. One type of indirect interaction is exploitative resource competition, which results from a reduction in plant biomass; another type is that caused by changes in plant traits. These are referred to as indirect effects, mediated, respectively, by biomass and plant traits. The two indirect effect types often occur simultaneously, and they are difficult to partition. To investigate the roles of the two indirect effects on both herbivores, a dynamic one-plant, two-herbivore system model was analyzed assuming the spatiotemporal co-occurrence of the herbivores and the plants’ non-specific induced defenses. Our analysis revealed that the densities of coexisting competitively superior and subordinate herbivores were regulated by negative indirect effects mediated by plant biomass and defense, respectively. This indicates that indirect effects mediated by plant biomass and plant traits can be important regulators of herbivore population size in equilibrium with herbivore coexistence. Our results could be generally applicable to plant–herbivore interactions with non-specific plant defense that is induced through both intra- and transgenerational responses. Keywords Plant–herbivore interaction . Induced defense . Indirect effect . Population dynamics
Introduction An ecological theory predicts that plant abundant in the terrestrial ecosystem is maintained by carnivore predation and/or disease of herbivores (HSS hypothesis, Hairston et al. (1960)), although a meta-analysis recently showed that terrestrial plant communities are controlled by top-down effects of herbivores, e.g., via reductions of plant biomass (Jia et al. 2018). Importantly, such top-down effects on plants possibly feed back to dynamics of herbivores. In plant–herbivore interactions on individual plants, two types of plant-mediated effects can alter competitive outcomes among herbivores. One effect Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12080-020-00479-2) contains supplementary material, which is available to authorized users. * Atsushi Yamauchi [email protected] 1
Center for Ecological Research, Kyoto University, Hirano 2-509-3, Otsu 520-2113, Japan
2
Ryukyu Sankei Co., Ltd., Okinawa, Japan
3
Osaka Prefecture University, Sakai, Japan
arises from a reduction in the host plant’s biomass, resulting in exploitative resource competition. Based on current consensus, which regards exploitative competition as an indirect interaction (Abrams 1987; Kaplan and Denno 2007; Schmitz 2009; Wootton 1994), this is referred to as an indirect effect mediated by plant bioma
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