Zooplankton Diversity and Dispersal by Birds; Insights From Different Geographical Scales

Dag O. Hessen,Thomas C. Jensen,Bjørn Walseng

doi:10.3389/fevo.2019.00074

Dag O. Hessen, Thomas C. Jensen + Show 1 more

Open Access

https://doi.org/10.3389/fevo.2019.00074

Copy DOI

Abstract

Given the major ecological and evolutionary role of dispersal abilities for organisms, as well as the current interest in species’ potential for further migration and colonization as a result of climatic changes or human-mediated invasions, our knowledge about dispersal abilities on spatial and temporal scales in many taxa is surprisingly limited. Zooplankton inhabit lakes and ponds that functionally are “aquatic islands” in the landscape, and both community composition and richness depend on their ability to disperse, and their post-dispersal colonization abilities. We here assess the diversity and dispersal of freshwater microcrustaceans based on three types of data; 1) > 2000 lakes on mainland Norway spanning a wide range in longitude, latitude and altitude, 2) a more limited number of ponds at Svalbard that are differently affected by migrating birds, and 3) immigration and colonization of recently constructed wetlands and man-made ponds. At all scales we discuss whether observed patterns in diversity can be explicitly linked to birds as vectors, or if confounding factors such as climate, productivity, age of locality – or other means of immigration, precludes conclusive evidence. The spatial patterns of zooplankton distribution strongly suggest that local sorting is a major determinant of richness and community composition. This sorting may not necessarily lead to similar community composition (the “quorum effect”) however. Despite the fact that rapid colonization occurs at local scales, and that birds undoubtedly can transmit animals or resting stages, their role in modulating community structure and richness is still an unsettled issue due to the many confounding parameters. The fact that birds often play a dual role in shaping diversity and community composition, first by direct dispersal, and secondly via affecting post-dispersal species sorting by changing water quality and productivity, is an important aspect of zoochory. Direct experimental evidence (colonization with and without bird exclusion), or genetic analysis of zooplankton species along migration routes, would however be the only ways to establish firm evidence for this case of zoochory.

Highlights

There are two principal drivers of biogeographical distribution patterns: the ability of species to disperse to new ecosystems, and the ability to establish permanent populations post dispersal
The ability and mechanisms for dispersal of aquatic organisms may differ with geographical range, ecosystem connectivity, dispersal vectors, and lake specific properties
The dispersal abilities of aquatic organisms is a matter of longstanding interests since Darwin’s seminal studies demonstrated how birds may serve as dispersal vectors for organisms attached to plumage or feet (Darwin, 1859; Bilton et al, 2001; Bohonak and Jenkins, 2003; Simonis and Ellis, 2014)

Summary

INTRODUCTION

There are two principal drivers of biogeographical distribution patterns: the ability of species to disperse to new ecosystems, and the ability to establish permanent populations post dispersal. Most shore-birds and waterfowl perform seasonal, long distance migration, and linking central Europe, Norway and the Svalbard archipelago, e.g., barnacle geese (Branta leucopsis) and purple sandpiper (Calidris maritima) (Figure 3) Both inland and subalpine wetlands are nesting sites for a large number of waders and ducks, but still possess modest or low zooplankton richness. Both these deltas are important stopover sites for migratory water birds, and bird-mediated dispersal could partly explain the high microcrustacean diversity where local sorting is less pronounced owing to the favorable habitats with a high number of available niches This is still at best circumstantial evidence since there is no conclusive evidence of bird-mediated zoochory in shaping community composition or richness at these scales, not the least due to the large number of confounding factors. The proximity to the large lake Øyeren implies a high likelihood of local dispersal by birds

Findings

DISCUSSION

CONCLUSION