Toward Ecological Holism: Discerning Pattern, Process and Scale Across the Productivity Landscape

Abstract

Life is self-regulating because it is productive; capturing, storing, and passing energy through trophic compartments of the food web. Our current measurement frameworks for biological productivity rely heavily on measuring biomass in relation to first-order climatic factors, but this approach is insensitive to the mediating factors of genetics and adaptive capacity, metabolism and physiology, and ecological interactions and processes. Productivity is thus an emergent property of ecosystem function, based on the collective metabolism of hosts and symbionts, interactions between species, and the flux of nutrients and energy across multiple levels of biological organization. The human enterprise is changing the structure and function of ecological systems around the world. As natural resources are degraded by pollution, nutrient loading, disturbance, and climate instability, ecosystems are being pushed past critical thresholds resulting in loss of biodiversity and declines in productivity. The internal processes of natural ecosystems are self-correcting, conditioned on the adaptive traits of organisms as they respond to local environmental conditions and each other. Foregoing chemoautotrophic ecosystems in extreme environments, oxygenic photosynthesis assembles the organic compounds upon which all terrestrial and aquatic ecosystems persist. Throughout the biosphere, symbiotic relationships mediate many physiological processes, from soil fungi providing nutrients for plant growth, to gut microbes metabolizing vitamins important to human health, all of which can change the metabolism, well-being, and productivity of hosts. I considered the elements of freshwater and forest ecosystems from which to reframe an understanding of ecological productivity, as trait-based and metabolism-driven, at multiple spatial scales of disturbance and across divergent ecological compartments. The work of this dissertation was to identify how shifts in small-scale physiological responses to disturbance pervade to large-scale ecological function. Understanding the internal processes of ecological stability requires integration of genetic traits and the phenotypic plasticity of those traits (i.e., adaptive capacity), within the broader context of the total environment. That is, there is a need to scale up and scale down. I integrated ecological productivity and disturbance at three spatio-ecological scales: (i) At the landscape level, I analyzed how disturbance influenced the distribution of bacteria with genetic traits for antibiotic resistance (a response to disturbance). I sampled 137 km of longitudinal river distance, from pristine headwaters to Superfund site near Seattle, Washington, USA. Antibiotic resistance was more prevalent in tributaries and in moderate to highly developed stream banks, but resistance was not detected along river segments with intact riparian vegetation. (ii) To evaluate secondary productivity at the host-symbiont level, I collected bacteria that were carrying traits for antibiotic resistance from a polluted urban lake and introduced cultures of these organisms to microcosms of the keystone species, Daphnia magna. I measured the somatic growth, reproduction, and nutritional status of the Daphnia after 30-days. Results indicated secondary productivity was modulated by symbionts in different ways according to the primary ecology of the symbiont. (iii) I evaluated the primary productivity of forest ecosystems at the climatic-regional level with a calculated index, “ecosystem fit,” (total net primary productivity/ theoretical maximum primary productivity) to estimate ecological resilience and scope-for-growth. Primary productivity was independent of tree leaf-traits, but phenology interacted divergently with climatic variables in extreme climates. Increases in biomass were associated with latitudinal gradients and seasonal forcing at the regional scale, and more closely associated with topographic and edaphic characteristics at the forest-stand scale. My analyses indicated that we can accurately predict which forests will be less resilient based on their current level of ecosystem fit and responsiveness across the full range of climatic regimes. With climate destabilization, we need to consider ecosystem function as emergent to all biotic and abiotic components that vary with scale. Each ecosystem is unique, and the most important variables will differ between them, and variable importance will change with scale, both within and between, different ecosystems. Ultimately, ecosystem properties are based on the collective metabolism of the dominant host species and all its symbionts, the collective phenotypic traits of the host-symbiont, and the genetic capacity for those traits to respond to environmental change.