Invasive plants-Chihuahuan Desert, Erodium cicutarium-Chihuahuan Desert, Desert ecology, Allelopathy, Competition (Biology), Desert ecosystem, Density-dependent competition
Understanding the mechanisms that allow invasive plants to be successful in introduced areas is an important field of study in plant ecology, as great effort and economic resources are spent annually to control the widespread of these often highly adaptable species. While it is very tempting to want to simply view invasive exotic species as simply "bad" for the environment, it is important to consider how exotic species reshape the habitat and landscape and how they influence plant and faunal assemblages and interactions, both at an overall community level and at a species to species level. In this study, I use the Chihuahuan Desert invasive, Erodium cicutarium, as a model to explore invasive strategies in maintaining plant community dominance after colonization. In particular, I investigate the seemingly facilitative relationship E. cicutarium has with a Chihuahuan native, Astragalus nuttallianus, through inter- and intra- specific seed and seedling competition trials and density-dependent germination experiments. I also look at E. cicutarium's potential to produce and secrete allelopathic biochemicals into the soil-- a defensive strategy many invasives tend to acquire only after being introduced into a new area-- through invasive leachate concentration experiments as well as soil chemical retention experiments. In my study I found that E. cicutarium germination was negatively correlated with interspecific seed density, but positively correlated with intraspecific seedling density. Contrastingly, A. nuttallianus germination was most negatively impacted by the presence of invasive seedlings. Additionally, E. cicutarium leachate tests showed a significant negative effect on Lepidium lasiocarpum (another Chihuahuan native) germination rates and timing but not with A. nuttallianus. Surprisingly, in both the E. cicutarium leachate concentration tests and the soil chemical retention test, I found potentially facilitative effects on Lesquerella gordonii (another Chihuahuan native) germination rates and timing (although, sample size complicates these findings' significance). These results suggest that the relationship between E. cicutarium and A. nuttallianus may not be directly facilitative, but rather, a toleration of the invasive that creates open niche spaces for it to colonize. While these results also suggest that E. cicutarium is, in fact, able to secrete allelochemicals that delay germination, they also suggest that these negative effects may be species specific, thereby leading to potential positive, nutrient-enabling legacy effects for some native species. If such findings are accurate to what is actually found in the field, environmentalists and conservationists may have to re-think the way they approach invasive plant species.
Danguilan, Samantha Jo, "Rethinking the antagonistic role of "invasive weeds" within plant communities : a case study from the Chihuahuan Desert" (2015). Honors Project, Smith College, Northampton, MA.
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