I believe that the autochthonous primary production plays an important role in the transfer of energy through food webs in tropical streams.
Macroinvertebrates (stream dwelling insects including grazers, shredders, gatherers, filterers, and predators), in stream-ecosystem exploit the physical characteristics of streams to obtain their foods.
Macro invertebrates are influenced by both bottom-up and top down forces in streams. The physical environment of streams places many constraints on organisms as well as on the type and form of food that is available.
Physical heterogeneity, including the substrate (material on or from which an organism lives, grows, or obtains its nourishment) and the current velocity of a stream channel, is an important factor that may influence local biotic diversity, nutrient dynamics,algae and macrophyte distribution, retention and distribution.
The following reference (a review) may be a good resource
Reference
J. Bruce Wallace and Jackson R. Webster.1996. The role of macro invertebrates in stream ecosystem function. Annu Rev. Entomol. 41:115-139
http://www.faculty.biol.vt.edu/webster/webster%20publications%20pdfs/wallace%20and%20webster%201996.pdf
Autochthonous energy is certainly important in all streams, even those that are considered "heterotrophic". There is evidence from several stable isotope studies in tropical streams that suggests most of the invertebrates and fish acquire their carbon from algae rather than from detritus (e.g., March and Pringle 2001, Mantel et al. 2004, Brito et al. 2006, Lau et al. 2009). However, some newer research from my lab (not yt published) incorporated the amount of invertebrate and fish production in Brazilian streams. When the actual amount of material that was consumed and assimilated is accounted for, it again appears that most of the energy moving through the food web was allochthonous in origin. So, even though most of the individual organisms may be herbivores or predators of herbivores, most of the production was through detritivores. This is a question that is not settled however, so it is difficult to say with any certainty if autochthonous or allochthonous energy assimilated into stream food webs is important to forests (which will likely be context-dependent on the specific conditions of your study location).
Energy content / transfer is one measure of the relative importance of auto- vs. alloch energy / carbon sources. There is also the issue of nutritional quality. This is perhaps why some stable isotope studies show a more aquatic diet than would be assumed by purely bulk amounts in the system. The C:N and C:P stoichiometry and fatty acid content of different food sources play an important role here and differ greatly among food sources. For example, inverts that based on mouth parts and behavior would be "strict" detritivores have algal markers (fatty acids, SI) in their guts and tissues. Whether inverts select foods based on their nutritional content is not yet settled.
Both energy inputs are important for streams, but autochthonous energy should be especially prominent in midsized, open-canopied streams according to the River Continuum Concept. This is consistent with my past work on Goose Creek, VA (Vadas 1990). Besides this spatial pattern, there is a temporal trend. Allochthonous production is most important in the cold (fall/winter) season via leaf fall (for aquatic invertebrates) and terrestrial invertebrates (for drift-feeding fishes like salmonids, as emergence of aquatic insects is limited then).
-Bob Vadas, Jr.
Vadas, R.L. Jr. 1990. The importance of omnivory and predator regulation of prey in freshwater fish assemblages of North America. Environmental Biology of Fishes 27: 285-302 (cf. http://springerlink.com/content/r532l217v0816611).
- Badges
- Science topic
- Similar topics
- Geoscience
- Asia
- India