Mechanisms, effects, and scales of dispersal in freshwater zooplankton

Abstract

The distribution of organisms can be regulated by local environmental factors and regional processes such as dispersal. Here, we review recent work on the role of dispersal for generating population and community structure in freshwater zooplankton. We examine evidence for different mechanisms of dispersal among lakes, for the effects of dispersal limitations on populations and communities, and for the effects of spatial scale on dispersal rates. Zooplankton move via human or animal vectors, flowing surface waters, and wind; the relative importance of the different modes of transport is poorly understood. Several lines of evidence suggest that dispersal among lakes separated over short spatial scales (Ͻ10 km) is sufficiently rapid that local interactions should limit species diversity and composition more than the supply of colonists. However, dispersal limitation over broad scales (tens to thousands of kilometers) might constrain geographic ranges and influence community structure. The current explosion in the incidence of exotic species indicates that such global-or continental-scale dispersal was limiting in the past. The spread of exotic species also provides opportunities to study the scale dependence of zooplankton dispersal. We show how patterns of range expansion can be used to estimate the change in invasion likelihood with distance to a source population. Such dispersal functions provide a crucial link between small-scale experimental studies and broad-scale geographic patterns.Theories of geographic structure in communities and populations come from two broad schools of thought. The regional approach examines the importance of movement of individuals and the colonization of isolated patches of habitat separated over broad spatial scales. Parallel theories have been developed for regional control of both genetic variation in populations (Slatkin 1985) and species diversity in communities (MacArthur and Wilson 1963). The regional approach often emphasizes neutral or drift processes such as colonization and extinction and ignores differences among species or environments (Hubbell 2001). By contrast, the local approach examines the response of species to conditions that influence population growth rates within relatively small, homogeneous patches of habitat (MacArthur 1972). Local-scale ecology focuses on differences among organisms or habitats that allow coexistence of multiple species or genotypes. The local and regional views have both enjoyed 1 Corresponding author (johnhavel@smsu.edu).

Role of diapause in dispersal and invasion success by aquatic invertebrates

“…Human-mediated vectors have been discussed by many authors (Carlton 1996;Gollasch & Leppäkoski 1999;Bilton et al 2001;Minchin & Gollasch 2002;Havel & Shurin 2004). Dispersal by human vectors are usually viewed as "introductions", either intentional or unintentional (Carlton 1999).…”

“…Natural mechanisms and vectors of dispersal of aquatic invertebrates have been discussed in detail in recent reviews by Bilton et al (2001), Bohonak & Jenkins (2003), and Havel & Shurin (2004). Diapausing eggs or cysts of aquatic invertebrates have been often considered as potential agents of dispersal by natural vectors, and even depicted in the literature as adaptations for dispersal (Maguire 1963;Korovchinsky & Boikova 1996).…”

“…Currents in marine ecosystems and rivers may be an important vectors for dispersal of active and diapausing invertebrates (Minchin & Gollasch 2002;Havel & Shurin 2004). Dispersal of gemmules of sponges by currents (as well as by fish, and waterfowl) is discussed by Fell (1998).…”

“…Some intercontinental transfers of diapausing eggs of aquatic invertebrates and their subsequent invasions of inland waters have been linked to the introduction of commercially useful plants (McKenzie & Moroni 1986), importation of industrial equipment (see review by Havel & Shurin 2004), and even transportation of the military amphibian vehicles (see case study of Daphnia parvula below). However, at present the majority of biological invasions into coastal and even inland waters worldwide can be linked to unintentional introductions via different shipping-related vectors: construction of canals, ships hull fouling and ballast water release.…”

“…The problem of the degree and mode of dispersal of aquatic invertebrates, first considered by Forel in classic ecological treatise "Le Leman" (1892,1895,1904), has attracted the growing attention of biologists (Shurin 2000;Bilton et al 2001;De Meester et al 2002;Cáceres & Soluk 2002;Figuerola & Green 2002;Havel et al 2002;Bohonak & Jenkins 2003;Havel & Shurin 2004). These papers provide a broad range of opinions (sometimes contradictory) concerning the scales, rates, and relative importance of various vectors in dispersal of aquatic organisms.…”