Abstract
The success of non-native, invasive species may be due to release from natural enemies, superior competitive abilities, or both. In the Sonoran Desert, Erodium cicutarium has increased in abundance over the last 30 years. While native species in this flora exhibit a strong among-species trade-off between relative growth rate and water-use efficiency, E. cicutarium seems to have a higher relative growth rate for its water-use efficiency value relative to the pattern across native species. This novel trait combination could provide the non-native species with a competitive advantage in this water-limited environment. To test the hypothesis that E. cicutarium is able to achieve high growth rates due to release from native herbivores, we compared the effects of herbivory on E. cicutarium and its native congener, Erodium texanum. We also compared these two species across a range of environmental conditions, both in a common garden and in two distinct seasons in the field, using growth analysis, isotopic compositions and leaf-level gas exchange. Additionally, we compared the competitive abilities of the two Erodium species in a greenhouse experiment. We found no evidence of herbivory to either species. Physiological measurements in a common environment revealed that E. cicutarium was able to achieve high growth rates while simultaneously controlling leaf-level water loss. Non-native E. cicutarium responded to favourable conditions in the field with greater specific leaf area and leaf area ratio than native E. texanum. The non-native Erodium was a stronger competitor than its native congener in a greenhouse competition experiment. The ability to maintain relatively higher values of water-use efficiency:relative growth rate in comparison to the native flora may be what enables E. cictarium to outcompete native species in both wet and dry years, resulting in an increase in abundance in the highly variable Sonoran Desert.
Highlights
One primary goal in invasion biology is to understand how non-native species are able to outcompete native species and increase in abundance in their introduced range (Levine et al, 2003; Bossdorf et al, 2005; Richardson and Pysek, 2006; Moles et al, 2012)
At the University of Arizona’s Desert Laboratory in the Sonoran Desert, we have identified a trade-off between leaflevel water-use efficiency (WUE) and relative growth rate (RGR) in the winter annual plant community, such that species with high RGR have low WUE and vice versa (Angert et al, 2007, 2009; Huxman et al, 2008; Kimball et al, 2013)
We focused on mechanisms that may have determined the success of E. cicutarium in our Sonoran Desert winter annual system
Summary
One primary goal in invasion biology is to understand how non-native species are able to outcompete native species and increase in abundance in their introduced range (Levine et al, 2003; Bossdorf et al, 2005; Richardson and Pysek, 2006; Moles et al, 2012). It is possible that invasive species are successful because they possess specific life history or physiological traits that allow them to outcompete natives (Rejmanek, 1996; Rejmanek and Richardson, 1996; Kolar and Lodge, 2001; Sakai et al, 2001). Non-native species may be successful because they are physiologically superior to native species in terms of their ability to capture and use resources (Funk and Vitousek, 2007). These traits that frequently characterize non-natives often trade off with the ability to tolerate predation, so a release from natural enemies may allow populations with such traits to succeed in new environments
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