Food web structure and basal resource utilization along a tropical
island stream continuum, Puerto Rico.
Abstract: Tropical stream food webs are thought
to be based primarily on terrestrial resources (leaf litter) in small forested
headwater streams and algal resources in larger, wider streams. In tropical
island streams, the dominant consumers are often omnivorous freshwater
shrimps that consume algae, leaf litter, insects, and other shrimps. We
used stable isotope analysis to examine (1) the relative importance of
terrestrial and algal-based food resources to shrimps and other consumers
and determine (2) if the relative importance of these food resources changed
along the stream continuum. We examined 15N
and 13C signatures
of leaves, algae, macrophytes, biofilm, insects, snails, fishes, and shrimps
at three sites (300, 90, and 10 m elev.) along the Río Espíritu
Santo, which drains the Caribbean National Forest, Puerto Rico. Isotope
signatures of basal resources were distinct at all sites. Results of two-source
13C mixing models
suggest that shrimps relied more on algal-based carbon resources than terrestrially
derived resources at all three sites along the continuum. This study supports
other recent findings in tropical streams, demonstrating that algal-based
resources are very important to stream consumers, even in small forested
headwater streams. This study also demonstrates the importance of doing
assimilation-based analysis (i.e., stable isotope or trophic basis of production)
when studying food webs.
March, J. and C. Pringle. 2003. Food web structure and basal resource utilization along a tropical island stream continuum, Puerto Rico. Biotropica 35: 84-93.
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