COMMUNITY ECOLOGY Ecosystems unit Today s Big Ideas: An organism s biotic environment includes Other individuals in its own population Populations of other species living in the same area An assemblage of species living close enough together for potential interaction is called a community. How species interact with each other (Community Ecology) How matter and energy flow within and through an ecosystem (Ecosystem Ecology) Interspecific Interactions Interspecific Competition (/) Interspecific interactions are interactions between species. In interspecific (between species) competition, the population growth of a species may be limited by Interspecific Competition Mutualism Predation Herbivory Parasites and Pathogens Mutualism (+/+) In mutualism, both species benefit from an interaction. One example is the mutualistic relationship of coral animals and the unicellular algae that live inside their cells. The coral gains energy from the sugars produced by the algae. The algae gain The population densities of competing species By the density of its own population Predation (+/) Predation refers to an interaction in which one species (the predator) kills and eats another (the prey). Numerous adaptations for predator avoidance have evolved in prey populations through natural selection. A secure shelter Access to light Carbon dioxide Ammonia, a valuable source of nitrogen 1
Herbivory (+/) Herbivory is the consumption of plant parts or algae by an animal. s have evolved numerous defenses against herbivory, including Spines Thorns Chemical toxins Parasites and Pathogens (+/) s and animals can be victims of Parasites, an animal that lives in or on a host from which it obtains nutrients Pathogens, disease-causing Bacteria Viruses Fungi Protists (Malaria) Trophic Structure Trophic structure is the feeding relationships among the various species in a community. A community s trophic structure determines the passage of energy and nutrients from plants and other photosynthetic organisms To herbivores And then to predators Figure 20.15-1 Figure 20.15-2 Figure 20.15-3 2
Quaternary Tertiary Tertiary Figure 20.15-4 Figure 20.15-5 Food Webs Detritivores, which are often called scavengers, consume detritus, the dead material left by all trophic levels. Decomposers are prokaryotes and fungi, which secrete enzymes that digest molecules in organic material and convert them into inorganic forms. Few ecosystems are as a simple as an unbranched food chain. Omnivores Eat producers and Form woven ecosystems called food webs What would happen if one of the predators in a food web were taken out? Lab 09 will help us to understand the consequences Some definitions: A keystone species is a species whose impact on its community is much larger than its total mass or abundance indicates. Experiments in the 1960s demonstrated that a sea star functioned as a keystone species in intertidal zones of the Washington coast. Dominant Species - a species in a community whose population is most abundant or which has the highest biomass. They may control what other species are present within the community. Foundation Species - ecosystem engineer ; a species that plays a major role in shaping communities by creating and enhancing a habitat that benefits other species. 3
ECOSYSTEM ECOLOGY An ecosystem includes The community of species in a given area All the abiotic factors, such as Energy Soil characteristics Water A simple terrarium is a microcosm that exhibits the two major processes that sustain all ecosystems: Energy flow, the passage of energy through the components of the ecosystem Chemical cycling, the use and reuse of chemical elements such as carbon and nitrogen within the ecosystem Energy Flow in Ecosystems All organisms require energy for Growth Maintenance Reproduction In many species, locomotion Energy Flows Through Ecosystems Watch energy flow animation on class website! Remember photosynthesis! Sunlight energy is stored as chemical energy in glucose. Remember cellular respiration! Chemical energy stored by plants is harvested by the organism to do work and is released as heat. You will see that at each step, the total amount of energy in the system decreases. WHY? http://facweb.northseattle.edu/csheridan/biology160_wi n11/movies/20_25energy_flow.html (There is no sound for this animation. Keep pressing the Play button to progress through the animation) Why did the energy decrease at each step? Let s look at how much energy we start with in an ecosystem: Production The amount, or mass, of living organic material in an ecosystem is the biomass. The rate at which an ecosystem s producers convert solar energy to the chemical energy stored in biomass is primary production The rate of primary production varies with the ecosystem Open ocean Estuary Algal beds and coral reefs Desert and semidesert scrub Tundra Temperate grassland Cultivated land Northern coniferous forest (taiga) Savanna Temperate broadleaf forest Tropical rain forest 0 Lots of primary production! 500 1,000 1,500 2,000 2,500 Average primary productivity (g/m 2 /yr) 4
Why did the energy decrease at each step? Let s look at how much energy is available to each trophic level as we move through a food chain: A pyramid of production illustrates the cumulative loss of energy with each transfer in a food chain. The energy level available to the next higher level Ecological Pyramid When energy flows as organic matter through the trophic levels of an ecosystem, much of it is lost at each link in the food chain. Ranges from 520% Is illustrated here as 10% This energy is stored as biomass and is then available to the next consumer The energy available to top-level is small compared to the energy available to lower-level. This explains why Chemical Cycling in Ecosystems Life depends on the recycling of chemicals. Nutrients are acquired and waste products are released by living organisms. At death, decomposers return the complex molecules of an organism to the environment. The pool of inorganic nutrients is used by plants and other producers to build new organic matter. Top-level require more geographic area Most food chains are limited to three to five levels The Carbon Cycle Photosynthesis Cellular respiration Watch Carbon cycle animation on class website! (Click Hide quantities ) http://facweb.northseattle.edu/csherid an/biology160_win11/movies/20_32c arbon_cycle.html Autotrophs In summary: The flow of matter and energy within and through an ecosystem The cycling of carbon between the biotic and abiotic worlds is accomplished mainly by the reciprocal metabolic processes of Heterotrophs (primary consumer) Producer (secondary consumer) Energy Light Chemical elements Detritus Decomposer Inorganic compounds (chemical elements) Figure 20.UN04 5