Modelling the effects of substituting pollinators in decline

Abstract: While pollination is essential for many plant species and ecosystem functions, pollinator populations worldwide are declining. This decline is largely due to abiotic changes in the environment: climate change and other anthropogenic impacts, such as pesticides and land use change. Against this background, I investigate the effects of introducing a non-native pollinator species ("substituting invader") in a pollination network with declining resident pollinators. In particular, I ask 1) whether interspecific competition is a necessary driver for local extinctions of resident pollinator species after environmental changes; and 2) how much the pollination benefits for the resident plants differ between a pollination network including a substituting invader and a network without. To answer this, a standard Lotka-Volterra competition model is extended with terms accounting for mutualism (pollination) and adaptation to the environment. I model a community of two resident plants, as well as two resident pollinators and a substituting invader. I find that interspecific competition is a necessary driver for local pollinator extinction following an abiotic change in the environment. The competitive effect of the substituting invader on resident pollinators is therefore negative, although a minor indirect benefit is observed for one resident pollinator species. However, the resident plants benefit from the introduction of a substituting invader, which leads to a small relative change in the plant population numbers.