Limits to the niche and range margins of alien species

Abstract

We discuss the apparent paradox that while introduced populations often adapt rapidly to conditions in the new range, it is normally assumed that the species’ niche remains unchanged. Focusing on plants, we argue that studies of the niche dynamics of alien species are useful for understanding the constraints acting on species in their native ranges, and vice versa. Most hypotheses about species ecological range margins are more consistent with there being a niche shift than niche stasis in the new range. After reviewing the evidence for niche shifts in alien species, we suggest that the probability of a shift occurring depends primarily upon the ecological and genetic processes limiting the species in its native range. For example, a fundamental niche shift might occur if introduced individuals are released from maladaptive gene flow from central populations, or if genetic diversity is increased by the mixing of individuals from different sources. In addition, other factors such as species characteristics, introduction history and conditions in the new range may also influence whether a niche shift occurs. Based on these considerations, we propose conditions under which niche shifts are most likely. Such understanding is important for predicting and mitigating current and future anthropogenic impacts on species ranges.

Distributional patterns of endemic, native and alien species along a roadside elevation gradient in Tenerife, Canary Islands

“…Alien species were absent from plots located at high elevation, consistent with previous observations (Pauchard and Alaback 2004), suggesting that i) the observed decline of alien species richness with elevation is probably due to the lack of introduction of alien species adapted to grow at high elevations (McDougall et al 2005, Alexander and Edwards 2010, Siniscalco et al 2011, and ii) niche boundaries provide the fundamental constraints for the spread of alien species ). These results confirm the predictions of the directional ecological filtering hypothesis that have been used to explain invasions of alien species in mountain regions.…”

Annual monitoring reveals rapid upward movement of exotic plants in a montane ecosystem

“…For example, while we have direct observations that many exotics can germinate and grow at much higher elevations than previously reported, we cannot be sure that these species can actually complete their life cycles at those highest elevations. In such cases, observations that do not represent self-sustaining populations are outside of their fundamental niches (Alexander and Edwards 2010). Distribution models should thus be calibrated using records that represent the ecological niche of the species.…”

“…A lower number of exotic species in a mountainous area, however, should not be misinterpreted as a high resistance to plant invasions (Pauchard et al 2009). This is especially true for many exotics that have not yet occupied all suitable regions in their introduced range (Alexander and Edwards 2010). Whether an introduced species will successfully invade a montane ecosystem depends on a range of factors such as species plasticity, local disturbance regime, biotic and abiotic resistance, and propagule pressure McDougall et al 2011;Molina-Montenegro et al 2012;Seipel et al 2012;Van Rensburg et al 2013).…”

Evolution under changing climates: climatic niche stasis despite rapid evolution in a non-native plant

“…For example, Franks et al [9] showed that Brassica rapa populations evolved advances in flowering time in response to shorter growing seasons caused by an extended drought. Other evidence comes from non-native plants, which often adapt rapidly to the changing climatic conditions that they encounter as they spread along environmental gradients [10].…”

“…Comparative studies of native and non-native populations of invasive species present an opportunity to test this prediction [10] and to explore the conditions under which evolutionary rescue might occur [12]. This is because many non-native species rapidly evolve clines in traits, such as growth and phenology, as they spread along climatic gradients in a new region [13,14].…”