Daelyn A. Woolnough

Using landscape ecology to understand and manage freshwater mussel populations

Abstract Mussel populations and the environments they inhabit are heterogeneous and fragmented. We review 3 areas in which principles of landscape ecology might be applied to the scientific understanding and management of freshwater mussels. First, recent studies show that hydraulics can be used successfully to delineate patches of mussel habitat, but additional variables such as host fish, food, or predators are probably important under certain conditions. However, research on patch dynamics in freshwater mussels is in its infancy, and we do not know if existing methods to delineate patches are adequate. Second, mussel ecologists are starting to think about the importance of connectivity among habitat patches. Major challenges will be to determine whether connectivity can be estimated in the field and whether human activities that reduce connectivity (e.g., dams) have produced large extinction debts in mussel populations. Third, we need to better understand the links between events on the watershed (e.g., timing and amounts of water, nutrient, and sediment inputs) and the quality, extent, location, and connections among patches of mussel habitats. Because of its focus on patterns and processes, landscape ecology has the potential to improve scientific understanding and management of mussel populations and, in particular, to help define the best spatial scales for scientific studies and management activities.

Insular lake island biogeography: using lake metrics to predict diversity in littoral zone mollusk communities

Abstract.  Island biogeography theory can be used to explain patterns of species richness on various types of habitat islands, including freshwater lake systems. Mollusk production in these systems also has been linked to various water-chemistry variables, such as pH, alkalinity, hardness, and specific conductance. We examined how mollusk diversity patterns were related to geographical and limnological factors in insular lakes of the Beaver and Manitou Archipelagos in Lake Michigan (Laurentian Great Lakes), USA. The strongest correlations observed were with shoreline development (r  =  0.80), specific conductance (r  =  0.87), and pH (r  =  0.87). Principal components analysis revealed that isolation by distance and PO43− concentration also may have affected species richness and abundance. Shoreline length was a better predictor of species richness than surface area, but both measures of habitat size were unable to account for much of the variation in species richness. The data suggest that shoreline length and development represent available habitat area more accurately than lake area for primarily littoral-dwelling mollusks. The relatively weak correlations observed with lake area and isolation from Lake Michigan suggest that application of island biogeography theory to predict mollusk species richness using only lake surface area and isolation by distance is limited for freshwater mollusks.

Coexistence of species with different dispersal across landscapes: a critical role of spatial correlation in disturbance

Disturbance is key to maintaining species diversity in plant communities. Although the effects of disturbance frequency and extent on species diversity have been studied, we do not yet have a mechanistic understanding of how these aspects of disturbance interact with spatial structure of disturbance to influence species diversity. Here we derive a novel pair approximation model to explore competitive outcomes in a two-species system subject to spatially correlated disturbance. Generally, spatial correlation in disturbance favoured long-range dispersers, while distance-limited dispersers were greatly suppressed. Interestingly, high levels of spatial aggregation of disturbance promoted long-term species coexistence that is not possible in the absence of disturbance, but only when the local disperser was intrinsically competitively superior. However, spatial correlation in disturbance led to different competitive outcomes, depending on the disturbed area. Concerning ecological conservation and management, we theoretically demonstrate that introducing a spatially correlated disturbance to the system or altering an existing disturbance regime can be a useful strategy either to control species invasion or to promote species coexistence. Disturbance pattern analysis may therefore provide new insights into biodiversity conservation.

Phylogeography of the freshwater mussel species Lasmigona costata: testing post-glacial colonization hypotheses

Understanding genetic diversity across large spatial scales helps to reveal patterns of population structure. Mitochondrial DNA sequences and microsatellite loci were used to analyze the phylogeography of a common unionid species (Lasmigona costata) from the Laurentian Great Lakes and historically connected river drainages. Phylogeographic patterns were assessed to determine colonization routes into the Great Lakes following glacial recession. A suite of seven microsatellite loci were genotyped and a fragment of the mitochondrial gene COI was sequenced. Multiple analyses using microsatellite allele frequencies suggest at least two distinct genetic populations for L. costata. A total of seven hypothesized post-glacial dispersal scenarios were compared using isolation by distance to test the various dispersal models. Evidence was strongest for two post-glacial dispersal routes into the Great Lakes: one utilizing a connection between the Wabash and Maumee River watersheds, and one utilizing a connection between the Wisconsin River and Green Bay watersheds. A highly differentiated and monophyletic population of L. costata was identified in the Ozark Highlands, which may constitute a unique taxonomic entity.

Application and transferability of Great Lakes coastal wetland indices of biotic integrity to high quality inland lakes of Beaver Island in northern Lake Michigan

Biological indicators or indices of biotic integrity (IBI) have been developed for land management and regulatory agencies to categorize the condition of a given ecosystem. IBIs are more widely used in lotic systems and those that can be used over wide geographic regions or multiple systems are deemed most valuable. Lacustrine wetlands have intrinsic complexity and multidimensionality making them very difficult to classify. This, in turn, greatly affects the transferability of indices created for explicit regions and wetland types. Similarly, due to scarcity, relatively pristine reference conditions are seldom included in IBI calibration and represent a critical end of the disturbance continuum. The robustness and transferability of macroinvertebrate and fish IBIs created for fringing lacustrine and drowned river mouth wetlands of the Great Lakes for use in wetlands occurring in inland-lakes on islands within the Great Lakes were tested. Islands within the Laurentian Great Lakes contain unique and critical habitats that have received little attention, but also require specialized tools for monitoring and management. Inland-lake wetlands of Beaver Island, Lake Michigan, were ranked a priori along a disturbance gradient based on adjacent land use/cover. Transferability of the pre-existing Great Lakes IBIs was determined by correlating the site-specific IBI rank with the site-specific disturbance ranks. Results indicated that the IBIs were not directly transferable and may require substantial modification.

Discrete longitudinal variation in freshwater mussel assemblages within two rivers of central Michigan, USA

A primary focus in the study of lotic ecosystems involves understanding the relationship between changes in the physical environment and changes in biota along a longitudinal gradient. Previous studies examining riverine organisms, primarily fish and aquatic insects, have noted two commonly occurring upstream-to-downstream patterns: either the restriction of species to distinct zones (i.e., discrete variation), or the gradual accumulation of species with increasing distance from the headwaters (i.e., continuous variation). Like other riverine organisms, freshwater mussels exhibit longitudinal patterns in distribution and abundance; however, few studies have quantified these patterns and the environmental variables that influence them. This study examined longitudinal patterns in the assemblage structure of mussels in the Chippewa and Pine rivers, Michigan, United States. A stratified random sampling design was used to sample mussels at 54 sites and timed searches allowed for the characterization of mussel assemblages. Multivariate regression tree models revealed differences in mussel assemblage structure that are consistent with upstream-to-downstream changes in surficial geology and wetland habitat. Certain species were restricted to specific geologies suggesting discrete variation with k-means partitioning and non-metric multidimensional scaling supporting these results. Because the results were consistent between rivers, we expect these patterns to prevail in similarly glaciated regions.

Confirmation of Obovaria olivaria, Hickorynut Mussel (Bivalvia: Unionidae), in the Mississagi River, Ontario, Canada

Abstract A significant and recruiting population of Obovaria olivaria (Hickorynut Mussel) was confirmed in the Mississagi River, Lake Huron drainage, ON, Canada. This large river unionid mussel is known to use Acipenser fulvescens (Lake Sturgeon) and Scaphirhynchus platorynchus (Shovelnose Sturgeon) as hosts. The Mississagi River is known to have a spawning Lake Sturgeon population. In 9.1 person-hours of snorkel and SCUBA searches, 10 live O. olivaria ranging in length from 36 to 79 mm, including six gravid females, were collected in sandy substrates with water depths from 1.5 to 4 m. Obovaria olivaria in the Mississagi River represent a significant range disjunction from the other extant populations in Canada in the Ottawa and St. Lawrence river drainages. As the conservation status of this rare mussel in Canada is assessed, the geographic genetic population structure and spatial extent among known areas should be studied to understand the post-glacial redistribution of the species.