The role of ecological interactions in determining species ranges and range changes

Abstract

Climate has been widely regarded as the main determinant of the geographical distribution of species. Biotic interactions between co‐occurring species, however, are an important additional influence. We review the importance of interactions with food and nectar plants (as resources) in determining the distribution of phytophagous and pollinating insects (as consumers). We use biological recording datasets for seven taxonomic groups to quantify the relationship between the geographical distributions within Britain of 1265 phytophagous insects and their associated food plants, representing 9128 interactions in total. We find a consistent pattern across taxonomic groups in that individual phytophagous insect species rarely utilize the full range of their food plants and the relationship between the range sizes of insects and their food plants is not a simple linear one. For a small selection of phytophagous species where data are available, we highlight an association between changes in range and interactions with associated food plant species. Climate‐driven range expansion may be constrained through disruption of trophic relationships between phytophagous insects and their food plants if they respond differently to abiotic drivers. By contrast, range expansion may be facilitated by temporary escape from natural enemies and/or exploitation of novel food plants that enable a broader set of habitats to be utilized. In a changing environment, some existing interactions will be disrupted but opportunities for novel interactions will also emerge, producing new assemblages and changes in distributions that will be dynamic yet hard to predict. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, ●●, ●●–●●.

Ecological networks are more sensitive to plant than to animal extinction under climate change

“…Thus, climatic niche breadth and biotic specialization may be indirectly linked via species traits. Third, realized climatic niche breadth and biotic specialization will be directly linked if the distribution of specialized animal species is constrained by that of their resource plants, which has been demonstrated for antagonistic plant–animal interactions of butterflies and other phytophagous insects723, but not yet for animal species linked to plants by mutualistic interactions. In contrast to animals, plants may depend less on their animal partners because pollination and seed dispersal by animals are characterized by a high degree of animal redundancy24 and because many plants have evolved alternative regeneration loops, such as clonal propagation, autonomous self-pollination or the maintenance of persistent seed banks25.…”

“…Thus, climate change is likely to trigger a decline or even the local extinction of animal species that are constrained by the occurrence of specific plant partners723. However, as the most connected animals seem to be relatively tolerant to projected changes in climatic conditions, climate change may only have weak indirect impacts on ecological networks via top-down effects from animals to plants.…”

“…Such bottom-up effects may be particularly severe for animal groups that depend on plant resources throughout their life cycle (that is, in the larval and adult stage) and are restricted to specific resource types, such as many insect taxa723, rather than for animals that are able to use alternative resources, such as most birds37. Indeed, a high risk of extinction cascades from lower to higher trophic levels has been shown for specialized plant–insect interactions13.…”

When are species invasions useful for addressing fundamental questions in plant biology?

“…Since invasive species spreading in their new range will likely encounter novel biotic interactions, they also provide a model for how range expansion of native species will be impacted by changes in biotic interactions. For example, the enemy release hypothesis, originally conceived to explain how a loss of natural enemies could lead to some species becoming invasive upon introduction, may equally apply to native species, as they may also leave natural enemies behind as their range expands (reviewed by Stewart et al, 2015 ).…”

“…Since invasive species spreading in their new range will likely encounter novel biotic interactions, they also provide a model for how range expansion of native species will be impacted by changes in biotic interactions. For example, the enemy release hypothesis, originally conceived to explain how a loss of natural enemies could lead to some species becoming invasive upon introduction, may equally apply to native species, as they may also leave natural enemies behind as their range expands (reviewed by Stewart et al, 2015 ).Th e use of invasive species as models to explore how and whether species adapt to changing conditions is gaining interest, yet many questions remain unaddressed. Future directions include determining the factors that infl uence evolutionary change during spread, in particular those factors that infl uence spread itself.…”