ELECTIVES > THE ROLE OF ANIMALS IN ECOSYSTEMS DYNAMICS

This course covers in depth some of the important roles that animals play in organizing and controlling ecosystem processes, structure and function. These topics are outlined below in the section on Course Content. The course is organized as discussion of primary literature led first by the instructor and then by students. The first section is a structured lecture and discussion of pre-selected material, while the second section is a student led discussions of topics they have selected and researched. The course meets twice a week for 1.5 hrs. each time.

 In the first section, the first class of the week is a lecture by the instructor to introduce the roles of animals in ecosystems. The second class of the week is a structured discussion of one or two selected reading around that week's theme. For example, I might give a lecture that discusses the role of animals as Ecosystem Engineers, and then in the second meeting we would discuss one or two papers that have documented the role of a particular animal as an engineer. Individual students would be assigned to lead the discussion of the papers for that week.

 The second section of the course focuses on student presentations and discussions of animals in ecosystems. Selection of the topic occurs in conjunction with the instructor during the first part of the course. Each student leads an in-class discussion and writes a final paper on his or her chosen subject.

At the end of the course we try to determine if there were any basic principals that would allow us to predict a priori if a particular animal might have an unique role in ecosystems, or if they are part of a general 'functional group'. Students will be encouraged to develop a project that they could use as their Semester in Environmental Science research project topic.

Assigned Reading:  Check assigned reading for each week- see syllabus below.

Class Structure and Grading:
Overall class participation (30%)
Oral presentation of their subject (30%)
Written report on their subject (40%)

Course Content:

In the past, ecology has progressed along two parallel but largely independent paths - ecosystem ecology and population/community ecology. Population and community ecology has focused on interactions between individuals and populations. Ecosystem ecology has focused on the flow and transformation of energy and matter. A growing number of ecologists are now working at the interface of population/community ecology and ecosystem ecology as we have begun to understand that the species that make up ecosystems have important effects on ecosystem functions.

 Although species interact in ecosystem processes in many ways, two major mechanisms are trophic interactions and modification of their surroundings. Trophic interactions are expressed through food webs and have led to important concepts such as 'keystone' species and 'trophic cascades'. Although initially developed to describe a species' role in defining community structure, the term 'keystone' has been extended to include species whose removal results in a significant change in community structure or ecosystem function.

 Organisms that modify, maintain and/or create habitats have been termed 'ecological engineers'. A key characteristic of an 'ecosystem engineer' is that it changes the availability of resources used by other organisms beyond the biomass provided by it's own population. Engineering is not direct trophic support, but rather the activities of the animal (burrowing, mixing, or production of exoskeleton) alter hydrology, nutrient cycles, soil stability fertility, current speeds etc. resulting in a markedly different ecosystem. In this sense these species are 'keystone species' - species whose removal has big effects on ecosystem functions.

 Our understanding of the importance of species composition on ecosystem function is probably the greatest for plants in terrestrial ecosystems. For example, the kinds of trees in the forest affect understory species composition and the weather because evergreens and deciduous trees intercept and retain water and sunlight differently. Decomposition rates and nutrient cycling are also affected because the leaves of different species have characteristic chemical compositions that alter their rates of decay and release of nutrients.

 Increasingly we have realized that animals can also be important in ecosystem function. In terrestrial ecosystems, animals may affect ecosystem function by influencing the physical factors important to nutrient cycles. The physical shredding of leaf litter by arthropods speeds decomposition. Grazing by large mammals, such as deer or moose, alter forest succession, dramatically affecting biogeochemical cycling and response to disturbance. Large mammal fecal pellet deposition can concentrate nutrients and increase recycling providing focal points for plant establishment. In tropical forests, nitrogen and phosphorus cycling are highly dependent on soil infiltration, aeration and compaction. The creation of large macropores by the tunnel and nest building activities of ants creates conduits which accelerate the transportation of nutrients and results in microsite nutrient enrichment. In grasslands, gopher mounds exert a strong influence on the spatial pattern and temporal dynamics of the ecosystem. By bringing soil material up from underneath to the surface and killing the surrounding vegetation by burying it in up to 10 cm of soil, gophers periodically create mounds of bare soil. Plant succession on these "microhabitat islands" subsequently takes place and controls the landscape level plant community. In general the importance of small mammals such as pocket gophers in structuring a variety of plant communities has been increasingly appreciated.

 In some aquatic ecosystems, we also have evidence for the importance of animals in controlling ecosystem processes. Probably the best known example in marine systems is the sea otter/sea urchin/kelp system. Removal of sea otters released sea urchins from predator control resulting in the loss of kelp beds. In addition to the direct effects, loss of kelp also changed wave action, suspended sediment load and siltation rates with profound consequences for other inshore flora and fauna. Another example, San Francisco Bay, illustrates the importance of animals in mediating human-induced changes in ecosystems. In San Francisco Bay phytoplankton levels are much lower than in other estuaries as a result of a combination of factors in which filter feeding bivalves play a major role. Cropping by bivalves helps prevent phytoplankton blooms and periodic oxygen depletion. The importance of bivalve grazing pressure was conclusively demonstrated by the impacts of a bivalve on San Francisco Bay phytoplankton, zooplankton and benthos. Another well known example is the effect sediment infauna have on the physical, chemical and biological properties of sediments. The production of fecal pellets, tests and shells alters the physical structure of sediments while the feeding and burrowing of infauna increases porewater circulation, affecting the transport of dissolved materials, oxygen distribution and nutrient fluxes.

 Changes in the populations of these animals, through harvesting, toxic pollution or habitat alteration, may radically alter ecosystem processes. Integrating population and community dynamics with biogeochemistry is an important step if we are to fully understand what controls the long-term stability of ecosystems. Preservation, restoration, and recovery of systems may be slowed or not possible if populations that control important ecosystem properties are not preserved.

 In this course, we will examine questions such as:

 Are there fundamental roles of animals or specific feedback mechanisms by which animals regulate ecosystem function, such as physical mixing, that occur across a wide variety of ecosystems?

Does the importance of animals in controlling ecosystem function increase as from the arctic to the tropics?

What is the value of animal diversity to ecosystem function?

Course Syllabus:

Week 1: Roles of Animals in Ecosystems - Overview

 Increasingly we have begun to understand that animals may play important roles in controlling ecosystem dynamics. Although species interact in ecosystem processes in many ways, two major mechanisms are trophic interactions and modification of their surroundings by their behaviors. In this lecture, we will discuss some of the basic roles of animals in ecosystems.

Week 1 assigned readings:
Chew, R. M. (1974). "Consumers as regulators of ecosystems: an alternative to energetics." The Ohio Journal of Science 74: 359-371.
Kitchell, J. F., R. V. O'Neill, et al. (1979). "Consumer regulation of nutrient cycling." BioScience 29: 28-34.
Lawton, J. H. 1994. What do species do in ecosystems? Oikos 71:367-374.
Mills, L. Scott, M. Soule and D. Doak. 1993. The keystone-species concept in ecology and conservation. BioScience 43: 219-224.

Week 2: Top Down Control

 Through food web interactions animals can exert 'top-down control' in ecosystems. They can control the diversity and size structure of plants and animals and set a limit on total ecosystem productivity.

Week 2 assigned readings:
Carpenter, S. R., J. F. Kitchell, et al. (1985). "Cascading trophic interactions and lake productivity." BioScience 35: 634-639.
McKendrick, J. D., G. O. Batzli, et al. (1980). "Some effects of mammalian herbivores and fertilization on tundra soils and vegetation." Arctic and Alpine Research 12: 565-578.
Bell, R. H. V. (1971). "A grazing ecosystem in the Serengeti." Scientific American 230: 86-93.

Week 3: Nutrient Cycling

 Animals can influence nutrient cycling of ecosystems by translocating nutrient via migration, by transformation during the process of feeding, or by storage in a biomass pool. Some examples of this are the translocation of P to P-poor freshwater lakes by salmon returning to spawn, zooplankton vertical migration in the open ocean, the regeneration of ammonium by menhaden during feeding in an estuary, and storage of P in the bones of fishes in lakes.

Week 3 assigned readings:
Deegan, L. A. (1993). "Nutrient and energy transport between estuaries and coastal marine ecosystems by fish migration." Can. J. Fish. Aquat. Sci. 50: 74-79.
Krokhin, E. M. (1975). Transport of nutrients by salmon migrating from the sea into lakes. Coupling of Land and Water Systems. A. D. Hasler, Springer-Verlag New York Inc.: 153-156.
Zlotin, R. I. and K. S. Khodashova (1975). The Role of Animals in Biological Cycling on Forest-Steppe Ecosystems. R. I. Zlotin and K. S. Khodashova, Dowden, Hutchison & Ross, Inc., Stroudsburg, PA: 1-116. (read only pages 1-30).

Week 4: Landscape Structure

 Organisms that modify, maintain and/or create habitats have been termed 'ecological engineers'. A key characteristic of an 'ecosystem engineer' is that it changes the availability of resources used by other organisms beyond the biomass provided by it's own population. Engineering is not direct trophic support, but rather the activities of the animal (burrowing, mixing, or production of exoskeleton) alter hydrology, nutrient cycles, soil stability fertility, current speeds etc. resulting in a markedly different ecosystem.

Week 4 assigned readings:

Hall, S. J., D. J. Basford, et al. (1991). "Patterns of recolonization and the importance of pit-digging by the crab Cancer pagurus in a subtidal sand habitat." Marine Ecology Progress Series 72: 93-102.
Naiman, R. H., J. M. Melillo, et al. (1986). "Ecosystem alteration of boreal forest streams by beaver (Castor canadensis)." Ecology 67: 1254-1269.
Nelson, C. H. and K. R. Johnson (1987). "Whales and walruses as tillers of the sea floor." Scientific American ??: 112-117.

Weeks 5-10: Student led discussions of literature.

 

SELECTED REFERENCES

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Baes, C. F., H. E. Goeller, et al. (1977). "Carbon dioxide and climate: the uncontrolled experiment." American Scientist 65: 310-320.

Bazely, D. R. and R. L. Jefferies (1985). "Goose Feces: a source of nitrogen for plant growth in a grazed salt marsh." Journal of Applied Ecology 22: 693-703.

Bedard, J., J. C. Therriault, et al. (1980). "Assessment of the importance of nutrient recycling by seabirds in the St. Lawrence Estuary." Canadian Journal of Fisheries and Aquatic Sciences 37: 583-588.

Bell, R. H. V. (1971). "A grazing ecosystem in the Serengeti." Scientific American 230: 86-93.

Bertness, M. D. (1985). "Fiddler crab regulation of Spartina alterniflora production on a New England salt marsh." Ecology 66: 1024-1055.

Bjorkstrom, A. (1979). "Man's global redistribution of global carbon." AMBIO 8: 254-259.

Bray, R. N., A. C. Miller, et al. (1981). "The fish connection: a trophic link between plankton and rocky reef communities?" Science 214: 204-205.

Bray, R. N., L. J. Purcell, et al. (1986). "Ammonium excretion in a temperate-reef community by a planktivorous fish, Chromis punctipinnis (Pomacentriadae), and potential uptake by young giant kelp, Macrocystis pyrifera (Laminariales)." Marine Biology 90: 327-344.

Cargill, S. M. and R. L. Jefferies (1984). "The effects of grazing by lesser snow geese on the vegetation of a sub-arctic salt marsh." Journal of Applied Ecology 21: 669-686.

Carpenter, R. C. (1981). "Grazing by Diadema antillarum (Philippi) and its effects on the benthic algal community." Journal of Marine Research 39: 749-765.

Carpenter, R. C. (1984). "Predator and population density control of homing behavior in the Caribbean echinoid Diadema antillarum." Marine Biology 82: 101-108.

Carpenter, S. R., J. F. Kitchell, et al. (1985). "Cascading trophic interactions and lake productivity." BioScience 35: 634-639.

Carpenter, R. C. (1985). "Sea urchin mass-mortality: effects on reef algal abundance, species composition, and metabolism and other coral reef herbivores." Proceedings of the Fifth International Coral Reef Congress, Tahiti 4: 53-60.

Carpenter, R. C. (1985). "Relationships between primary production and irradiance in coral reef algal communities." Limnology Oceanography 30: 784-793.

Chew, R. M. (1974). "Consumers as regulators of ecosystems: an alternative to energetics." The Ohio Journal of Science 74: 359-371.

Cross, F. A., J. N. Willis, et al. (1975). Role of juvenile fish in cycling of Mn, Fe, Cu, and Zn in a coastal-plain estuary. Estuarine Research. L. E. Cronin, Academic Press, Inc.: 45-63.

Deegan, L. A. and B. J. Peterson (1992). "Whole-river fertilization stimulates fish production in an Arctic tundra river." Can. Journ. Fish. and Aquat. Sci. 49(9): 1890-1901.

Deegan, L. A. (1993). "Nutrient and energy transport between estuaries and coastal marine ecosystems by fish migration." Can. J. Fish. Aquat. Sci. 50: 74-79.

Deegan, L. A., J. T. Finn, et al. (1997). Flow model analysis of the effects of organic matter--nutrient interactions on estuarine trophic dynamics. Denmark, Sweden, Olsen & Olsen.

Durbin, A. G., S. W. Nixon, et al. (1979). "Effects of the spawning migration of the alewife, Alosa pseudoharengus, on freshwater ecosystems." Ecology 60: 8-17.

Durbin, E. G. and A. G. Durbin (1983). "Energy and nitrogen budgets for the Atlantic menhaden, Brevoortia tyrannus (Pisces: Clupeidae), a filter-feeding planktivore." Fisheries Bulletin 81: 177-199.

Eggers, D. M. (1977). "The nature of prey selection by planktivorous fish." Ecology 58: 46-59.

Ellis, J. E., J. A. Wiens, et al. (1976). "A conceptual model of diet selection as an ecosystem process." Journal of Theoretical Biology 60: 93-108.

Finegan, B. (1984). "Forest succession." Nature 312: 109-114.

Fontier, S. (1978). "Interface entre deux ecosystemes: exemple dans le domaine pelagique." Annales de institut Oceanographique 54: 95-106.

Gaines, S. D. and J. Roughgarden (1987). "Fish in offshore kelp forests affect recruitment intertidal barnacle populations." Science 235: 479-481.

Gallucci, V. F. (1973). "On the principles of thermodynamics in ecology." Annual Review of Ecology and Systematics 4: 329-357.

Gray, L. J. (1993). "Response of insectivorous birds to emerging aquatic insects in riparian habitats of a tallgrass prairie stream." Am. Midl. Nat. 129: 288-300.

Guillet, A. and R. W. Furness (1985). "Energy requirements of a Great white pelican (Pelecanus onocrotalus) population and its impact of fish stocks." Journal of Zoology, London 205: 573-583.

Hall, C. A. S. (1972). "Migration and metabolism in a temperate stream ecosystem." Ecology 53: 585-604.

Hall, S. J., D. J. Raffaelli, et al. (1990). "The importance of flatfish predation and disturbance on marine benthos: an experiment with dab Limanda limanda (L.)." Journal of Experimental Marine Biology and Ecology 136: 65-76.

Hall, S. J., D. Raffaelli, et al. (1990). "Predator-caging experiments in marine systems: a reexamination of their value." The American Naturalist 136: 657-672.

Hall, S. J., D. Raffaelli, et al. (1990). "The role of the predatory crab, Liocarcinus depurator, in a marine food web." Journal of Animal Ecology 59: 421-438.

Hall, S. J., D. J. Basford, et al. (1991). "Patterns of recolonization and the importance of pit-digging by the crab Cancer pagurus in a subtidal sand habitat." Marine Ecology Progress Series 72: 93-102.

Hobbie, J., J. Cole, et al. (1984). "Role of biota in global CO2 balance: the controversy." BioScience 34: 492-498.

Hoffman, J. A., J. Katz, et al. (1984). "Fiddler crab deposit-feeding and meiofaunal abundance salt marsh habitats." Biological Ecology 82: 161-174.

Hughes, J. E., L. A. Deegan, et al. (1998). Nitrogen flow through the food web in the oligohaline zone of a New England estuary. Ecology.

Kitchell, J. F., J. F. Koonce, et al. (1975). "Phosphorus flux through fishes." Verh. Internat. Verein. Limnol. 19: 2478-2484.

Kitchell, J. F., R. V. O'Neill, et al. (1979). "Consumer regulation of nutrient cycling." BioScience 29: 28-34.

Krokhin, E. M. (1975). Transport of nutrients by salmon migrating from the sea into lakes. Coupling of Land and Water Systems. A. D. Hasler, Springer-Verlag New York Inc.: 153-156.

Lawton, J. H. 1994. What do species do in ecosystems? Oikos 71:367-374.

Lewin, R. (1985). "Gregarious grazers eat better." Science 228: 567-568.

Longhurst, A. (1983). "Benthic-pelagic coupling and export of organic carbon from a tropical Atlantic continental shelf-Seirra Leone." Estuarine, Coastal and Shelf Science 17: 261-285.

Lovvorn, J. R. and M. P. Gillingham (1996). "Food dispersion and foraging energetics: a mechanistic synthesis for field studies of avian benthivores." Ecology 2: 435-451.

McKendrick, J. D., G. O. Batzli, et al. (1980). "Some effects of mammalian herbivores and fertilization on tundra soils and vegetation." Arctic and Alpine Research 12: 565-578.

Meyers, J. H. and K. S. Williams (1984). "Does tent caterpillar attack reduce the food quality of red alder foliage?" Oecologia (Berlin) 62: 74-79.

Mills, L. Scott, M. Soule and D. Doak. 1993. The keystone-species concept in ecology and conservation. BioScience 43: 219-224.

 Minshall, G. W. (1978). "Autotrophy in stream ecosystems." BioScience 28: 767-771.

Naiman, R. H., J. M. Melillo, et al. (1986). "Ecosystem alteration of boreal forest streams by beaver (Castor canadensis)." Ecology 67: 1254-1269.

Nakashima, B. S. and W. C. Leggett (1980). "Natural sources and requirements of phosphorus for fishes." Canadian Journal of Fisheries and Aquatic Sciences 37: 679-686.

Nelson, C. H. and K. R. Johnson (1987). "Whales and walruses as tillers of the sea floor." Scientific American ??: 112-117.

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Nixon, S. W. and V. Lee (1980). The Flux of Carbon, Nitrogen and Phosphorus Between Coastal Lagoons and Offshore Waters. Unesco Publication.

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Peterson, B. J. and J. M. Melillo (1985). "The potential storage of carbon caused by eutrophication of the biosphere." Tellus 37B: 117-127.

Peterson, B. J., L. Deegan, et al. (1993). "Biological responses of a tundra river to fertilization." Ecology 74(3): 653-672.

Pringle, C. M. (1996). "Attyid shrimps (Decapoda: Atyidae) influence the spatial heterogeneity of algal communities over different scales in tropical montane streams, Puerto Rico." Freshwater Biology 35: 125-140.

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Wasserrug, R. (1984). "Why tadpoles love fast food." Natural History 4: 60-68.

Wharton, w. G. and K. H. Mann (1981). "Relationship between destructive grazing by the sea urchin, Strongylocentrotus droebachiensis, on the Atlantic Coast of Nova Scotia." Can. J. Fish. Aquat. Sci. 38: 1339-1349.

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Zlotin, R. I. and K. S. Khodashova (1975). The Role of Animals in Biological Cycling on Forest-Steppe Ecosystems. The Role of Animals in Biological Cycling on Forest-Steppe Ecosystems. R. I. Zlotin and K. S. Khodashova, Dowden, Hutchison & Ross, Inc., Stroudsburg, PA: 1-116.

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