Dept. Publications

Bios

Biosphere


Contact


Department of Biology

18111 Nordhoff Street
Northridge, CA 91330-8303

Phone: (818) 677-3356
Fax: (818) 677-2034

Email:biology.dept@csun.edu

Office Location:
Eucalyptus Hall 2102

Hours:
Mon-Fri: 8:00am-5:00pm

Map

Photo of Steve R. Dudgeon.

Steve R. Dudgeon

Assistant Professor

Ph.D. University of Maine

email: steve.dudgeon@csun.edu
Phone: (818) 677-7322
Fax: (818) 677-2034
Office: Eucalyptus Hall 2207

My research interests lie in two areas. One is the different levels of integration exhibited among individual organisms aggregated in a group, clone or colony and how this variation impacts both, their population ecology, and the evolution of their life histories. The second is the scale- and context-dependence of ecological processes in community development. I study both benthic marine invertebrates and seaweeds for three reasons: first, both taxa are easily manipulated in field and laboratory experiments, second interactions between these taxa are often central features of community organization and third, a great diversity of unitary and clonal lifestyles (often in a single lineage) coexist in one ecosystem.

Life history evolution in clonal taxa

In many clonal eukaryotes variation in morphology and life history traits often are correlated and show concordant plasticity during development, but relatively little is known about the underlying physiology. Here, we seek to determine from laboratory experiments, primarily, whether the correlation between morphology and life history traits in clonal organisms is causal. This research employs colonial hydrozoans (Phylum Cnidaria). Colonies consist of individuals (polyps) connected to one another by a network of circulatory tubes (stolons) that define a colonyís morphology. The transport of fluid through the colonyís stolons emerges from the collective behavior of oscillating polyps. Variation in colony form and polyp behavior generates variation in flow patterns within this gastrovascular system that underlies different developmental patterns and demographic schedules, implying that colony morphology is self-maintaining through the differential expression of pattern-forming genes in response to internal fluid transport. Research to date suggests that patterns of vascular connections codetermine life history and morphology,and that the evolution of life history traits is constrained by physiological and developmental mechanisms before selection can eliminate unfit variants.

Scale- and context-dependence of ecological processes

The ecological processes that generate pattern in communities are well known. How these processes vary in importance across different spatial and temporal scales and, thereby, contribute added variation to patterns in space and time is less well known. For instance, the signatures left by historical events may affect interactions between species in present-day communities. Current research employs field and laboratory experiments to address two related questions: (1) under what spatial and temporal scales and environmental conditions do historical events mediate processes that influence species distribution and abundance?, (2) how do the strengths, or nature, of interactions between species differ in different environmental backgrounds?

My research in the Gulf of Maine suggests that large scale historical events, such as may occur from severe ice scour, can initiate the origin of either rockweed or mussel bed communities at a given site. Alternative communities may arise because disturbances over large areas affects subsequent rates of recruitment and predation during succession. If alternative states do exist, it implies that community transitions are threshold-dependent and that small scale perturbations that cross a threshold may cause large, irreversible changes in ecosystems. Non-linear responses by communities to environmental changes demand that our plans for managing ecosystems be sensitive to these phenomena.

Like the signatures left by historical events, the present environmental context affects interactions between species. My work on intertidal seaweeds has shown that species may compete in favorable environments, but not interact in more stressful environments. This interaction is mediated by physiological responses of each species to varying environments. Continued research will determine variations in the strength, or nature, of species interactions for taxa living together in different environments and how such variation within a target species pair affects other indirectly associated species. The goal is to better predict the dynamics of populations and the structure of communities by casting predictions of species interactions in an environment-dependent context.

Ecological significance of genet fusion among algal holdfasts.

Considerable evidence indicates that among clonal eukaryotic organisms large size is favored by selection. Often genets of a taxon can fuse to rapidly increase their size. In animals fusion is confined to kin, but in plants selection to develop historecognition systems during their evolution may have been weak relative to animals. Consequently, in red seaweeds (at least) cellular fusions are common, but its ecological significance is unknown. I plan to study the adaptive significance of holdfast fusion in suitable red algal species (e.g., on the Pacific coast, Gracilariopsis lemaeniformis). By acquiring suitable genetic markers for different genotypes and outplanting to the field different combinations of fused products (i.e., single clones, chimeras, etc.) of known identity, the demographic performance of each genet can be assessed. Fusions of holdfasts within and among clones may be adaptive for red algae, particularly those that inhabit space-limited, wave-swept shores. A long term goal is to determine if red algal species of different clades in similar habitats show convergence for this trait.

Representative Publications

Dudgeon, S. R., A. Wagner, J. R. Vaisnys, and L. W. Buss. Dynamics of gastrovascular circulation in the hydrozoan Podocoryne carnea: The one polyp case. The Biological Bulletin (in press).

Dudgeon, S. R., R. S. Steneck, I. R. Davison, and R. L. Vadas. Coexistence of similar species in a space-limited intertidal zone. Ecological Monographs (in press).

1996. Dudgeon, S. R. and L. W. Buss. 1996. Growing with the flow: On the maintenance and malleability of colony from in the hydroid, Hydractinia. The American Naturalist 147: 667-691.

Petraitis, P. S. and S. R. Dudgeon. Experimental evidence for the origin of alternative communities. Oikos (in press).

1998. Wagner, A., Dudgeon, S. R., J. R. Vaisnys, and L. W. Buss. 1998. Non-linear oscillations in polyps of the colonial hydroid Podocoryne carnea. Naturwissenschaften 85: 1-5.

Manuscripts in review

Dudgeon, S. R. and P. Petraitis. Scale-dependent recruitment: Altering rates of successional recovery or a mechanism of community divergence? (Ecology).

Dudgeon, S. R., J. E. Kübler, W. Wright, R. L. Vadas, and P. Petraitis. Limited dispersal of Ascophyllum nodosum zygotes under different hydrodynamic regimes. (Ecology).