Combining bottom-up and top-down analyses to test fundamental concepts in invasion biology

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Invasion biology investigates species that have been introduced to areas beyond their native range. Many of its fundamental concepts lack a firm empirical basis, e.g. the resistance hypothesis (which says that richer and less disturbed biota offer more resistance against invaders) or the enemy release hypothesis (which explains the success of invaders by their release from enemies, which are left behind in the native range). I propose to test these and other concepts by combining two approaches. First, I will create a global dataset of islands and continents with information on the number of animals and plants that were introduced to each of them, the number that established there, and the number that spread, separately for different taxonomic groups. The dataset will also provide information on the characteristics of the islands and continents (e.g. area, biodiversity, human population density). This top-down approach will provide a powerful test of the resistance hypothesis. Second, case studies of many individual invasion events exist, but this source of knowledge has not been used to investigate fundamental patterns in invasion biology. I propose to collectively analyze case studies and to compare the results of this bottom-up approach with those of top-down analyses (the one proposed above and previously published ones). Combining these two approaches will either support or help revising fundamental concepts in invasion biology.