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Niche conservatism may constrain the ability of species to colonize outside of their physiological niche. However, invasion may disrupt or otherwise alter the evolutionary forces that normally operate to limit niche expansion. Historical collections housed in university herbaria are ideal sources of distributional data for building predictive distributional models. In Silene vulgaris, niche models conditioned upon native range occurrences are significant predictors of the species’ range in North America. However, there is also a large area in the Northwest where S. vulgaris has expanded its niche outside the ancestral prediction. |
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Niche conservatism and expansion during range changes |
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Ecological niche model from a GARP analysis of 30 yr climate normals in Europe and North America. Shown are overlaid range predictions from the best subset of 10 models (shaded according to agreement among models). Yellow points are recorded occurrences in herbaria records or published literature and floras. |
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A little explored aspect of niche modeling during invasion is how population structure in the native range may lead to intraspecific variation in niche requirements among lineages, and different predicted areas of occurrence in the introduced range. Niche models built for the eastern and western European genetic demes (identified with AFLPs) support divergent niche predictions in eastern North America, The degree that genotypes match their predicted range varies with deme membership, suggesting that stochastic events during colonization by chance place genotypes inside or outside their ancestral niche. This random variance determines whether a particular invasion inoculum is pre-adapted to its environment, and may critically affect the success of establishing populations. |
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Intraspecific ecological niche models of Silene vulgaris demes from eastern (A) and western (B) Europe invading North America. Dark green shading indicates the species-wide prediction based on European occurrences. Black circles are genotypes belonging to each deme sampled in North America; size is proportional to sample size. Note how the eastern European deme (in yellow) largely matches its prediction niche, while the western European deme (in light green) is largely mismatched from its niche. |
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Publications:
S. R. Keller and D.R. Taylor. Departures from niche conservatism during a biological invasion. In prep. |