Filtering by
- All Subjects: Ecology
An understanding of the formation of spatial heterogeneity is important because spatial heterogeneity leads to functional consequences at the ecosystem scale; however, such an understanding is still limited. Particularly, research simultaneously considering both external variables and internal feedbacks (self-organization) is rare, partly because these two drivers are addressed under different methodological frameworks. In this dissertation, I show the prevalence of internal feedbacks and their interaction with heterogeneity in the preexisting template to form spatial pattern. I use a variety of techniques to account for both the top-down template effect and bottom-up self-organization. Spatial patterns of nutrients in stream surface water are influenced by the self-organized patch configuration originating from the internal feedbacks between nutrient concentration, biological patchiness, and the geomorphic template. Clumps of in-stream macrophyte are shaped by the spatial gradient of water permanence and local self-organization. Additionally, significant biological interactions among plant species also influence macrophyte distribution. The relative contributions of these drivers change in time, responding to the larger external environments or internal processes of ecosystem development. Hydrologic regime alters the effect of geomorphic template and self-organization on in-stream macrophyte distribution. The relative importance of niche vs. neutral processes in shaping biodiversity pattern is a function of hydrology: neutral processes are more important in either very high or very low discharge periods. For the spatial pattern of nutrients, as the ecosystem moves toward late succession and nitrogen becomes more limiting, the effect of self-organization intensifies. Changes in relative importance of different drivers directly affect ecosystem macroscopic properties, such as ecosystem resilience. Stronger internal feedbacks in average to wetter years are shown to increase ecosystem resistance to elevated external stress, and make the backward shifts (vegetation loss) much more gradual. But it causes increases in ecosystem hysteresis effect. Finally, I address the question whether functional consequences of spatial heterogeneity feed back to influence the processes from which spatial heterogeneity emerged through a conceptual review. Such feedbacks are not likely. Self-organized spatial patterning is a result of regular biological processes of organisms. Individual organisms do not benefit from such order. It is order for free, and for nothing.
Interdisciplinary research has highlighted how social-ecological dynamics drive the structure and function of the urban landscape across multiple scales. Land management decisions operate across various levels, from individuals in their backyard to local municipalities and broader political-economic forces. These decisions then scale up and down across the landscape to influence ecological functioning, such as the provisioning of biodiversity. Likewise, people are influenced by, and respond to, their environment. However, there is a lack of integrated research, especially research that considers the spatial and temporal complexities of social-ecological dynamics, to fully understand how people influence ecosystems or how the resulting landscape in turn influences human decision making, attitudes, and well-being.
My dissertation connects these interdisciplinary themes to examine three questions linked by their investigation of the interactions between people and biodiversity: (1) How do the social and spatial patterns within an arid city affect people’s attitudes about their regional desert environment? (2) How are novel communities in cities assembled given the social-ecological dynamics that influence the processes that structure ecological communities? (3) How can we reposition bird species traits into a conservation framework that explains the complexity of the interactions between people and urban bird communities? I found that social-ecological dynamics between people, the environment, and biodiversity are tightly interwoven in urban ecosystems. The regional desert environment shapes people’s attitudes along spatial and social configurations, which holds implications for yard management decisions. Multi-scalar management decisions then influence biodiversity throughout cities, which shifts public perceptions of urban nature. Overall, my research acts as a bridge between social and ecological sciences to theoretically and empirically integrate research focused on biodiversity conservation in complex, social-ecological systems. My goal as a scholar is to understand the balance between social and ecological implications of landscape change to support human well-being and promote biodiversity conservation.
I collected soil samples from the riparian and terrestrial zones of 21 sites, placing them in growth chambers at one of two temperature regimes, and monitoring emergence of seedlings for 12 weeks. Results showed an approximately equal number of warm and cool specialists in both riparian and terrestrials zones; generalists also were abundant, particularly in the riparian zone. The number of temperature specialists and generalists in the riparian zones did not differ significantly between perennial headwater and ephemeral stream types. In montane streams, alpha diversity of the soil seed bank was highest for ephemeral reaches; in basin streams the intermittent and perennial reaches had higher diversity. Spatial turnover was primarily responsible for within stream beta-diversity—reaches had different species assemblages. The large portion of temperature specialists found in riparian seed banks indicates that even with available moisture riparian zone plant community composition will likely be impacted by changing temperatures. However, the presence of so many temperature generalists in the riparian zones suggests that some component of the seed bank is adapted to variable conditions and might offer resilience in a changing climate. Study results confirm the importance of conserving multiple hydrogeomorphic reach types because they support unique species assemblages.