Food Web Studies

Ecology of  Invertebrates

Organic Matter  Processing

Publications

 

Food Web Studies

    A- The role of omnivory in structuring stream communities is potentially great in lowland neotropical streams that are characterized by an abundance of macroconsumers (i.e., fishes and shrimps) which consume both insects and algae. Our results show the importance of: (1) conducting experiments in a relatively natural depositional environment subject to natural background erosion and sloughing (i.e., use of electric exclosures); (2) evaluating effects of natural densities of both diurnal and nocturnal macroconsumers through time in the context of these natural abiotic effects; and (3) distinguishing between the response of different types of algal resources (e.g., diatoms versus greens and bluegreens) which are differentially affected by sedimentation and erosion.  We found no evidence of a trophic cascade.  Our findings are in agreement with the theoretical prediction that large-sized omnivores have strong direct trophic (feeding) effects, both on smaller primary consumers (insects) and basal resources (algae) (Pringle and Hamazaki 1998).

    B- The role of biotic factors (natural assemblages of omnivorous fishes) in controlling the response of primary producers to physical disturbance (frequent high discharge events).  Our results show that fishes play a key role in maintaining the stability of benthic algal assemblages and their resistance to storm events.  Furthermore, results suggest that in the absence of omnivorous fishes, high discharge events would play a major role in structuring benthic algal assemblages, resulting in extreme fluctuations in algal biomass (Pringle and Hamazaki 1997).

    C- Effects of macroconsumers (i.e., fishes and shrimps) on detritus and detritivores.  Results indicate that macroconsumers decrease densities of small invertebrates inhabiting leaf packs, mainly of collector-gatherers, and that decay rates of leaves are not affected by insect densities, but are affected by the presence of macroconsumers (Rosemond et. al. 1998).  In addition, studies assessing the role of macroconsumers vs. nutrients in controlling insect assemblages indicate that nutrients are more important than macroconsumers in controlling insect densities (Rosemond et al. 2001).

    D- Stable isotope ratios were measured in major trophic levels in three streams of varying trophic complexity that were located at two major Neotropical research sites:  La Selva in Costa Rica and Luquillo Experimental Forest in Puerto Rico.  In all streams, nitrogen isotopic values increased with increasing trophic position of the species.  The shrimp Macrobrachium was more of an omnivore in Costa Rica than in Puerto Rico.  Differences in isotopic values at the base of the food web between Puerto Rico and Costa Rica were attributed to larger contribution of remineralized nitrogen to and within the stream in Costa Rica (Kilham and Pringle 1998).

    E-Food web studies at La Selva have focused on the following objectives:  (1) assessing the bottom-up effects of geothermally-introduced phosphorus on benthic community structure and function;  (2) assessing the top-down controls on benthic insect assemblages by macroconsumers in phosphorus-rich and phosphorus-poor streams; and  (3) simulating the effects of geothermally-introduced phosphorus on benthic stream communities in a phosphorus-poor stream, through whole-stream phosphorus enrichment.  Results indicate that:  (1) accrual of algal standing crop is greater in geothermally-modified phosphorus-rich streams than in unmodified streams (Pringle et al. 1986); (2) instantaneous growth rates of detritivores (Chironomidae) are greater in high vs. low phosphorus stream water measured in the laboratory (Rosemond et. al. 2001). (3) top-down control on benthic insect assemblages by macroconsumers was similar in phosphorus-rich and phosphorus-poor streams (Ramírez and Pringle 2004). 

  F-Ecological Stoichiometry The range of dissolved phosphorous concentrations in La Selva streams results in a wide range of P-content in basal food resources (detritus and periphyton).  Phosphorous is an important element for growth and development.  We are measuring how consumers respond to the P-content of their food resources in terms of their body elemental composition, growth rates, RNA content, and rates of nutrient recycling.  Results indicate thatin high P streams, basal resources are enriched 5-fold and invertebrate consumers are enriched 2-fold in P-content (Small & Pringle, submitted).  This bottom-up stoiciometric effect of chronic nutrient loading over millenia extends to fishes, which recycle P at a greater rate in High-P streams.

Top    Home

    A- Benthic insect assemblage structure differs among stream habitats (riffles and pools).  Assemblage composition is similar to that reported for other areas in Central America and is dominated by the orders Ephemeroptera (Tricorythodes, Leptohyphes, Thraulodes, Baetis?), Coleoptera (Elmidae), and Diptera (mainly Chironomidae).  Collector-gatherers are the dominant functional-feeding group and very few shredders can be found.  Insect secondary production is low compared with temperate streams, most likely because of the dominance of non-insect invertebrates, such as shrimps.  Habitat-weighted secondary production was 373.16 mg AFDM m^-2 y^-1 (Ramírez and Pringle 1998).

    B- Invertebrate community composition was assessed along an altitudinal gradient from the Barva volcano (~3000 m.a.s.l.) to the lowlands (30 m.a.s.l.) using two sampling techniques: drift and Surber samplers.  Both sampling techniques indicated that Diptera (Chironomidae) and Ephemeroptera were the dominant insect groups at all sites. Disturbed streams draining banana plantations were dominated by Chironomidae and had lower taxon richness and diversity than other sites.  While data from benthic samples indicated that insects were the major faunal component (> 90%) at all sites, drift samples were dominated by larval shrimps (> 50%) at the 30 m and 50 m sites.  This study shows the importance of measuring invertebrate drift, in addition to directly sampling the benthos. Drift sampling provided data on a major community component (shrimps) of lowland tropical streams, that would have been overlooked using traditional benthic sampling techniques, and in some cases provided additional information on taxon richness.  Based on results of the present study, it is recommended that drift sampling be included as a standard complementary tool to benthic sampling in biological assessments (e.g., bioassessment protocols) of tropical streams, which are often characterized by migratory invertebrate species such as shrimps. Drift samples provide critical information on the presence or absence of shrimps and also on the timing and magnitude of their migration which is an important link between many tropical rivers and their estuaries (Pringle and Ramírez 1998).
    Mayfly (Ephemeroptera) community composition and structure was analyzed for three years at the Sábalo stream.  Composition was dominated by the family Leptohyphidae and Baetidae, with the first one as dominant in terms of density.  Both composition and densities presented large fluctuations over the study period, and were not related with rainfall nor was it consistent among years.  Species richness was high but density was low.  Fish predation seems to be the main factor controlling community structure (Flowers and Pringle 1995).

    C- Invertebrate drift densities are high in streams of La Selva compared with similar sized streams in other regions, however, benthic insect densities are relatively low.  Drift is dominated by larval shrimps in lowland reaches near large rivers and by insects in piedmont and mountain reaches (Ramírez and Pringle 2000).  Drift periodicity is strongly nocturnal, with peaks at 1800 h (sunset) and 0300 h.  Our results suggest that nighttime drift is driven by the presence of predatory diurnal drift-feeding fishes and nocturnal adult shrimps.  There are no clear seasonal patterns over both 'dry' and wet seasons, suggesting that benthic communities are subject to similar stresses throughout the year, and that populations grow and reproduce continuously (Ramírez and Pringle 1998, 2001). 

    D- Freshwater shrimp community composition- Current studies on the freshwater migratoryshrimp species of La Selva focus on the effect of stream solutes an stream morphology on species community composition, abundance, fecundity, and growth rates.  (The freshwater shrimp community in the streams of La Selva is composed primarily of Macrobrachium careinus, Macrobrachium heterochirus, and Macrobrachium oltersi.) 

Top    Home

A. Leaf litter breakdown was examined at La Selva as part of a latitudinal gradient that also included Michigan and Alaska.  Results indicate that while processing rates (per day) were fastest at the Costa Rica site (as expected), rates at the Alaska and Michigan sites were similar to each other, which we would not predict if temperature were the principal factor controlling breakdown rate. If using degree days eliminates any effect of differing thermal regimes, rates should be similar across latitudes; however, rates at the Alaska site were much faster (per degree day) than rates at the sites in Costa Rica and Michigan. Three hypotheses were suggested: (i) shredding insect populations have adapted to the local thermal regime, and invertebrate-mediated processing rates are either similar between regions (showing no latitudinal pattern), or increase with latitude; (ii) microbial populations are less active at colder temperatures, and the rate of microbially mediated processing of leaf litter will show a decrease with latitude, and consequently (iii) the relative importance of invertebrate v microbial processing changes on a latitudinal gradient, with invertebrates being more important at high latitudes (Irons et al. 1994).
 

B. Landscape variation in phosphorus concentration affects leaf breakdown rates. Our work has shown that decay rates of leaves,  fungal biomass, and invertebrate biomass follow a Michaelis-Menten relationship to soluble reactive phosphorus concentration (which varied between 5 and 250 µg/L among streams). Results suggest that differences in decay rates were the result of differences in microbial activity among streams (Rosemond et. al. 2002). Furthermore, macroconsumers decrease biomass of small invertebrates and increase decay rates of leaves (Rosemond et. al. 2001).

C.  Interactions between leaf litter quality and water phosphorus are being assessed to determine their effects on decomposition dynamics.  Specific objectives are to: 1) examine effects of initial leaf litter chemistry on breakdown processes in a Neotropical lowland stream and compare the results to a temperate site; 2) assess the influence of interactions between litter carbon quality and dissolved phosphorus on microbial and invertebrate leaf litter processing; and 3) use artificial substrates of varying carbon quality to examine microbial response to water nutrients.  Results to date suggest that initial concentrations of cellulose and lignin are important in determining leaf breakdown rates and microbial response to increased water phosphorus.
 
 

Top    Home

Marcelo Ardon measuring microbia respiration in the Carapa Stream

Don Stone (OTS Executive Director, 1976-1996) getting his feet wet checking out electric fish exclosures at La Selva

Ardon,  M., and C, M. Pringle.  2007.  Organic matter quality mediates heterotrophic biofilm response to phosphorus enrichment of the water column and substratum.  Freshwater Biology 52: 1762-1772.

Flowers, R. W. and C. M. Pringle. 1995. Yearly fluctuations in the mayfly (Ephemeroptera) community of a tropical stream draining lowland pasture in Costa Rica, Chapter 10. p. 131-149. In: Corkum, L. D. and J. J. H. Ciborowski (eds.) Current Directions in Research on Ephemeroptera. Canadian Scholars Press, Inc. Toronto 478 pp.

Irons, J. G., M. W. Oswood, R. J. Stout, and C. M. Pringle.  1994. Latitudinal patterns in leaf litter breakdown: is temperature really important?  Freshwater Biology 32: 401-411.

Kilham, S. S. and C. M. Pringle. 2000. Food webs in two neotropical stream systems as revealed by stable isotope ratios. Verhandlungen Internationale Verin. Limnol 27: 1768-1775.

Paaby, P., A. Ramirez, and C.M. Pringle. 1998. The benthic macroinvertebrate community in Caribbean Costa Rican streams and the effect of two sampling methods. Refista de Biologia Tropical 46: 185-199.

Pringle, C. M. and T. Hamazaki. 1997. Effects of fishes on algal response to storms in a tropical stream. Ecology 78: 2432-2442.

Pringle, C. M. and T. Hamazaki. 1998. The role of omnivory in a neotropical stream:  separating diurnal and nocturnal effects. Ecology 79: 269-280.

Pringle, C. M., P. Paaby-Hansen, P. D. Vaux, and C. R. Goldman. 1986. In situ nutrient assays of periphyton growth in a lowland Costa Rican stream. Hydrobiologia 134: 207-213.

Pringle, C. M. and A. Ramírez.  1998.  Use of both benthic and drift sampling techniques to assess tropical stream invertebrate communities along an altitudinal gradient, Costa Rica. Freshwater Biology 39: 359-373.

Ramírez, A. and C. M. Pringle. 1998. Structure and production of a benthic insect assemblage in a neotropical stream. Journal of the North American Benthological Society. 17:443-463.

Ramírez, A., P. Paaby, C.M. Pringle, and G. Aguero. 1998. Effect of habitat type on benthic macroinvertebrates in a tropical lowland stream, Costa Rica. Revista de Biologia Tropical 46:201-213.

Ramírez, A. and C. M. Pringle. 1999. Invertebrate drift and benthic community dynamics in a lowland neotropical stream, Costa Rica. Hydrobiologia 386: 19-26.

Ramírez, A.  and C. M. Pringle. 2001.  Spatial and temporal patterns of invertebrate drift in streams draining a neotropical landscape, Costa Rica. Freshwater Biology 46:47-62.

Ramírez, A., C.M. Pringle, and L. Molina. 2003. Effects of stream phosphorus levels on microbial respiration. Freshwater Biology 48:88-97.

Ramirez, A., and C.M. Pringle.  2004. Do macroconsumers affect insect responses to a natural stream phosphorus gradient? Hydrobiologia 515: 235-246.

Ramirez, A. , C. M. Pringle, and M. Douglas. 2006. Temporal and spatial patterns in stream physicochemistry and insect assemblages in a tropical lowland streams. Journal of the North American Benthological Society 25: 108-123.

Ramirez, A. and C. M. Pringle. 2006. Fast growth and turnover of chironomid assemblages in response to stream phosphorus levels in a tropical lowland landscape. Limnology and Oceanography 51:189-196.

Rosemond, A. D., C. M. Pringle, and A. Ramírez.  1998.  Macroconsumer effects on detritus and detritivores in a tropical stream. Freshwater Biology 39: 515-524.

Rosemond, A.D., C.M. Pringle, A. Ramírez, and  M.J. Paul. 2001. A test of top-down and bottom-up control in streams. Ecology 82:2279-2293.

Rosemond, A.D., C.M. Pringle, A. Ramirez, M.J. Paul, and J.L. Meyer. 2002. Landscape variation in phosphorus concentration and effects on detritus-based tropical streams. Limnology and Oceanography 47:278-289.

Stallcup, L. A., M. Ardon, and C. M. Pringle. 2006. Does nitrogen become limiting under high-P conditions in detritus-based tropical streams? Freshwater Biology. 51:1515-1526.

Dissertations

Ramírez, A. 2001. Control of benthic assemblages in detritus-based tropical streams. University of Georgia, Athens, GA.

Ardon, M. 2006. Exogenous versus endogenous control of microbially-mediated decomposition in lowland neotropical streams. University of Georgia, Athens, GA.

Small, G. In Progress. Resource-consumer stoichiometry along a natural phosphorus gradient in Neotropical stream food webs.  University of Georgia, Athens, GA.

Master's Theses

Stallcup, L. 2004. Effects of water chemistry and leaf species on leaf breakdown in neotropical headwater streams. University of Georgia, Athens, GA.

Ramírez, A. 1997. Structure, function and production of benthic macroinvertebrate communities in lowland tropical streams, Costa Rica. University of Georgia, Athens, GA.
 
 

Top    Home