Trait values and not invasive status determine competitive outcomes between native and exotic invasive species under varying soil nutrient availability
thesisposted on 2022-03-28, 15:44 authored by Samiya Tabassum
1. Invasion by exotic plants presents a major threat to global biodiversity and is often associated with nutrient enrichment of soils, particularly on soils of naturally low fertility. It is likely that the outcome of competitive interactions between native and exotic invasive plants may be mediated by soil nutrient availability. 2. I independently investigated competitive effect and response and the occurrence of asymmetric competition in a glasshouse experiment where seedlings of eight functionally similar pairs of exotic invasive and native species from low fertility Hawkesbury Sandstone derived soil were grown under low and high nutrient availability. 3. I tested the hypotheses that native species would be competitively superior in low nutrient environments because they employ a resource conservation strategy and exotic invasive species would be competitively superior in high nutrient environments because they employ a resource acquisition strategy. I also hypothesised that exotic invasive species would be more plastic in their response to increased nutrient availability compared to native species. 4. I found that nutrient availability did not mediate competitive interactions between exotic invasive and native species. Instead, two exotic invasive and one native species were competitively superior irrespective of nutrient availability. Competitively superior species displayed a mixture of both nutrient conservation and acquisition strategies in the low and high nutrient treatments. Exotic invasive species were also not found to have higher degrees of trait plasticity compared with native species. 5. Synthesis. This study provides evidence that the a priori classification of exotic invasive and native species does not predict competitive superiority at varying nutrient levels but rather species specific differences in trait values provide a competitive advantage in response to nutrient availability.