UC Riverside

Habitat loss and fragmentation are the leading causes of biodiversity loss and are considered to be the principal threats to the sustainability of the biosphere. Historically, fragmentation literature focuses on direct anthropogenic disturbances, such as deforestation and urbanization. However, many ecosystems now face novel disturbances, such as the invasion of non-native species and climate change-induced disturbances, further exasperating the rate of habitat loss and fragmentation. Thus, it is critical to understand the influence of these novel disturbance events on biodiversity in order to identify the long-term consequences of global change. My dissertation focused on two types of landscapes facing novel disturbances: 1) the invasion of an exotic plant species in California’s Coachella Valley, and 2) altered fire regimes in Joshua Tree National Park (JTNP).

Sahara Mustard (Brassica tournefortii; hereafter mustard), has invaded habitats throughout the arid southwestern United States, including five distinct sand habitats in the eastern Coachella Valley, California. I examined trends in ground-dwelling arthropod community structure concurrent with mustard invasion within those habitats from 2003‒2011. I found strong negative relationships with arthropods and mustard even when controlling for non-target environmental correlates and for potential factors that we suspected of mediating mustard effects.

My second study site took place in JTNP, where wildfire was once non-existent or exceedingly rare. However, fires are now increasingly common due to the invasion of non-native grass species – an invasion facilitated by climate change and an on-going nitrogen soil deposition from urban California. This altered fire regime has left behind varying patterns of landscape heterogeneity. Within this landscape, I quantified the influence of fire-induced spatial heterogeneity on ground-dwelling arthropods and small mammal communities. I found that community patterns of both arthropods and mammals varied based on type of heterogeneity. I also found that spatial heterogeneity increased movement patterns for a general small mammal.

My dissertation research focused on the influence of multiple species in two types of disturbed landscapes across multiple habitats to provide a broad, cohesive understanding of novel disturbances influence community structure and patterns. This multifaceted approach provides a more realistic tactic to the understanding the long-term consequences of novel disturbances.