15 Population Dynamics of Benthic Species on Tidal
Flats: the Possible Roles of Shorebird Predation
J. VAN DER MEER, T. PIERSMA, and J.J. BEUKEMA
15.1 Introduction
In late summer millions of shorebirds leave their breeding grounds in the
Arctic and move to tidal mudflats in the temperate and tropical zones. These
mudflats can either be used as stopover sites during migration, or as overwintering areas. Shorebirds necessarily have high feeding rates and the densities of these salient predators can be high. Not surprisingly, many researchers have asked the question what the impact is of shorebirds on their
intertidal invertebrate prey, and whether this impact may differ, for example,
between temperate and tropical regions (Piersma and Beukema 1993). Generally, two approaches have been adopted to answer these questions. First,
estimates of annual consumption by shorebirds were compared with annual
invertebrate production estimates. Second, experiments were carried out
using exclosure cages. We argue that neither of the two methods is very
relevant in answering the questions posed. We suggest a more appropriate, but
time-consuming, approach based on long-term observations.
15.2 Production-Consumption Comparisons
A widely applied approach in assessing the impact of migrating or overwintering shorebirds on intertidal invertebrates is the estimation of the
amount of annual invertebrate production that is on average consumed by
shorebirds. The published accounts that we were able to find (Table 15.1) suggest that consumption/production ratios vary around a value of 0.3 (range
0.12-0.52), a value that does not seem to consistently differ between temperate and tropical regions {Fig. 15.1}. Yet, two things should be kept in mind.
First, it may be seriously questioned whether the reliability of these published data allows any conclusions at all. Second, even if such conclusions as
Ecological Studies, Vol. 151
K. Reise (ed.) Ecological Comparisons
of Sedimentary Shores
© Springer-Verlag Berlin Heidelberg 200 1
Flats: the Possible Roles of Shorebird Predation
J. VAN DER MEER, T. PIERSMA, and J.J. BEUKEMA
15.1 Introduction
In late summer millions of shorebirds leave their breeding grounds in the
Arctic and move to tidal mudflats in the temperate and tropical zones. These
mudflats can either be used as stopover sites during migration, or as overwintering areas. Shorebirds necessarily have high feeding rates and the densities of these salient predators can be high. Not surprisingly, many researchers have asked the question what the impact is of shorebirds on their
intertidal invertebrate prey, and whether this impact may differ, for example,
between temperate and tropical regions (Piersma and Beukema 1993). Generally, two approaches have been adopted to answer these questions. First,
estimates of annual consumption by shorebirds were compared with annual
invertebrate production estimates. Second, experiments were carried out
using exclosure cages. We argue that neither of the two methods is very
relevant in answering the questions posed. We suggest a more appropriate, but
time-consuming, approach based on long-term observations.
15.2 Production-Consumption Comparisons
A widely applied approach in assessing the impact of migrating or overwintering shorebirds on intertidal invertebrates is the estimation of the
amount of annual invertebrate production that is on average consumed by
shorebirds. The published accounts that we were able to find (Table 15.1) suggest that consumption/production ratios vary around a value of 0.3 (range
0.12-0.52), a value that does not seem to consistently differ between temperate and tropical regions {Fig. 15.1}. Yet, two things should be kept in mind.
First, it may be seriously questioned whether the reliability of these published data allows any conclusions at all. Second, even if such conclusions as
Ecological Studies, Vol. 151
K. Reise (ed.) Ecological Comparisons
of Sedimentary Shores
© Springer-Verlag Berlin Heidelberg 200 1