Testing Darwin's Naturalization Hypothesis and Elton's Bio-resistance Hypothesis in North American Breeding Birds
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Skibinski, Emily G.
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Abstract
Invasive species cause environmental and ecological havoc, and it is of great importance to understand why and how they happen. Two influential hypotheses have long been at the center of debate around invasive species: Darwin's naturalization hypothesis, which states that invaders that are less closely related to natives will be more successful, and Elton's bio-resistance hypothesis, which states that communities with higher levels of biodiversity will be more difficult to invade. Many studies have been conducted to test these hypotheses, with mixed results. However, studies which examine these hypotheses through the lens of functional traits and functional diversity are rare. I use data from the Breeding Bird Survey (BBS) to analyze if the native functional diversity has any effect on the non-native species, and if the difference between native and non-native traits is larger, or smaller than expected by chance. I used four different measures of functional diversity: functional richness, functional evenness, functional diversion, and functional dispersion. I found that what affects the non-native species presence, proportion, or longevity is extremely variable depending on which functional diversity metric was used for the
native community, or the metric used to represent the non-natives. Additionally, at the surveyroute scale, Darwin’s hypothesis is neither supported nor refuted. At the scale of bird conservation region however, non-native birds tend to be less similar in mass and more similar in tarsus length to natives. I also found a trend towards bird communities being composed of more large species, even when only Passerines are examined. Overall, this study highlights several issues in the literature that attempts to solve Darwin’s conundrum and the invasion paradox: the metrics used to investigate these hypothesis matter significantly, and more examinations of how these hypotheses relate to functional diversity and functional traits need to be carefully conducted.
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2024-05-23
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