Abstract

The impact of multiple disturbances on populations could be synergistic or antagonistic via disturbance interaction and are considered to be provoked by alternation of the impact of an ecosystem disturbance due to the effect of a preceding disturbance. The impact of a focal disturbance can also change when a preceding disturbance alters the proportion of individuals in a population exposed to these disturbances (i.e., interaction exposure effects), although this effect has not been addressed to date. Herein, we propose and test interaction exposure effects by elucidating disturbance interactions between canopy gap formation and ungulate grazing. Based on a vegetation and seed bank survey conducted on an island in Hokkaido, northern Japan, we examined whether canopy openness changes the impact of ungulate grazing on the occurrence probability of palatable plant species through the facilitation of germination. Species occurrence in the seed bank significantly decreased with increasing canopy openness under the presence of grazing; however, it slightly increased under the absence of grazing, suggesting that gap creation, which facilitates germination, exposes the seed bank to ungulate grazing. Because disturbances of various types often modify the habitat structure, these proposed disturbance interactions are expected to operate within various ecosystems and taxa.

Highlights

  • The impact of multiple disturbances on populations could be synergistic or antagonistic via disturbance interaction and are considered to be provoked by alternation of the impact of an ecosystem disturbance due to the effect of a preceding disturbance

  • The occurrence probability within grazing plots was approximately one-tenth of that within exclosure plots when canopy openness was 65%, which was the maximum canopy openness in the studied quadrats (Fig. 2a). These results suggested that the interaction of two disturbances induced a synergistic impact on the occurrence probability of a plant species in the seed bank

  • We propose the existence of interaction exposure effects, in which a supportive disturbance expands or reduces the proportion of a population that is exposed to the main disturbance as yet another form of multiple disturbance interaction

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Summary

Introduction

The impact of multiple disturbances on populations could be synergistic or antagonistic via disturbance interaction and are considered to be provoked by alternation of the impact of an ecosystem disturbance due to the effect of a preceding disturbance. An example of interaction modification effects is that of savanna fires reducing the resistance of tree trunks to hurricanes, as rapid tree growth following fires results in low wood density[18] Both interaction chain and modification effects can reasonably explain the variations within disturbances’ impact on a population, we aim to consider the effect of disturbance interactions on population resilience[20,21], which could be influenced by changes in the proportion of individuals within a population that are exposed to a disturbance due to disturbance interactions. We did not include this framework to our focus

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