Ecosystem Ecology • The biological and physical components of the environment are a single interactive system in the concept of the ecosystem – A.G. Tansley coined “ecosystem” in 1935 Ecosystem = Ecosystem = A group of interacting populations and their physical environment. All interacting by a flow of energy and with their physical and chemical environments. Ecosystems can be Large Small Ecosystem Ecology • An ecosystem is a spatial concept. It has boundaries and can be viewed in the context of its surrounding environment – It is sometimes difficult to clearly separate ecosystems Simple Energy input from Ecosystem sun Model Producers Autotrophs (plants and other self-feeding organisms) Nutrient Cycling Consumers Heterotrophs (animals, most fungi, many protists, many bacteria) Energy output (mainly metabolic heat) Ecosystem Materials Plants Animals Ecosystem Ecology • Community structure varies in response to environmental conditions • Organisms, in part, define the abiotic environment through succession – Tress affect temperature in a forest – Phytoplankton can affect water temperature Energy and Materials • Inputs are exchanges from the surrounding environment into the ecosystem • Outputs are exchanges from inside the ecosystem to the surrounding environment • A closed ecosystem is one with no inputs; an open ecosystem receives inputs form the surrounding environment Ecosystems 1. Population Interactions 2. Energy Flow 3. Material Cycles Ecosystems 1. Population Interactions 2. Energy Flow 3. Material Cycles Modes of Nutrition • Autotrophs – Capture sunlight or chemical energy – Primary producers • Heterotrophs – Extract energy from other organisms or organic wastes – Consumers, decomposers, detritivores Role of Organisms • Producers (photoautotrophs) Primary Producers Photoautotrophs + + + = + Sunlight + water + CO2 + minerals = C6H12O6 O2 sugar oxygen Energy Materials Concept 21.1 Feeding Relationships • Each feeding category, or trophic level, is based on the number of feeding steps by which it is separated from autotrophs. Role of Organisms • Consumers 1. Herbivore 2. Carnivores 3. Omnivores 4. Parasites 5. Decomposers Role of Organisms • Consumers 1. Herbivore 2. Carnivores 3. Omnivores 4. Parasites 5. Decomposers Role of Organisms • Consumers 1. Herbivore 2. Carnivores 3. Omnivores 4. Parasites 5. Decomposers Role of Organisms • Consumers 1. Herbivore 2. Carnivores 3. Omnivores 4. Parasites 5. Decomposers Role of Organisms • Consumers 1. Herbivore 2. Carnivores 3. Omnivores 4. Parasites 5. Decomposers Concept 21.1 Feeding Relationships • The 1st trophic level consists of autotrophs or primary producers. • Autotrophs generate chemical energy from sunlight or inorganic chemical compounds. • This level also generates most of the dead organic matter in an ecosystem. Concept 21.1 Feeding Relationships • 2nd trophic level: • Herbivores that consume autotrophs; also includes detritivores that consume dead organic matter. • 3rd (and higher) trophic levels: • Carnivores that consume animals from the level below. Feeding Relationships • Dead organisms and feces are consumed by organisms called detritivores (primarily bacteria and fungi), in a process called decomposition. • Detritus is considered part of the 1st trophic level, and detritivores are part of the 2nd level. Concept 21.1 Feeding Relationships • Some organisms do not conveniently fit into trophic levels. • Omnivores feed at multiple trophic levels. • Example: Coyotes are opportunistic feeders, consuming vegetation, mice, other carnivores, and old leather boots. Concept 21.1 Feeding Relationships • All organisms are either consumed by other organisms or enter the pool of dead organic matter (detritus). • In terrestrial ecosystems, only a small portion of the biomass is consumed, and most of the energy flow passes through the detritus. Energy Flow through Detritus Feeding Relationships • Much of the detritus in streams, lakes, and estuaries is derived from terrestrial organic matter. • These external energy inputs are called allochthonous inputs. • Energy produced by autotrophs within the system is autochthonous energy. Food Chain marsh hawk • A straight-line sequence of who upland sandpiper eats whom • Simple food garter snake chains are rare in nature cutworm plants Trophic Levels • Feeding relationships – All organisms at a trophic level are the same number of steps away from the energy input into the system • Autotrophs are producers – closest to energy input – first trophic level Food Chain 4th trophic level 3rd trophic level 2nd trophic level 1st trophic level Trophic Levels in a Desert Ecosystem Food Webs • A food web is a diagram showing the connections between organisms and the food they consume. • It shows qualitatively how energy flows from one component of this ecosystem to another. Food Webs • As more organisms are added to a food web, complexity increases to reflect the complexity of real ecosystems. • Feeding relationships can span multiple trophic levels (omnivory) and may even include cannibalism (circular arrows). Food Web marsh hawk Connections in a tallgrass prairie food web Higher Trophic crow Levels upland sandpiper garter snake frog weasel badger coyote spider Second Trophic Level sparrow earthworms, insects prairie vole pocket gopher ground squirrel First Trophic grasses, composites Level Fig. 30-4, p.529 Food Webs Are Complex Trophic Cascades • Trophic cascade: Series of trophic interactions that result in changes in biomass and species composition. • Predation by a top carnivore (4th level) decreases abundance of 3rd level carnivores, which leads to an increase in herbivores (2nd level), and then a decrease in primary producers. Trophic Cascades • What controls energy flow through ecosystems? • The “bottom-up” view: – Resources that limit producers determine energy flow through an ecosystem. Trophic Cascades • The “top-down” view: – Energy flow is governed by predator consumption rates at the highest trophic level, which influences multiple trophic levels below them. Trophic Cascades • In reality, both controls are operating simultaneously in ecosystems. • Top-down control has implications for the effects of trophic interactions on energy flow. Biological Magnification Non-degradable or slowly degradable substances become more and more concentrated in tissues of organisms at higher trophic levels of a food web DDT in Food Webs • Synthetic pesticide banned in United States since 1970s • Carnivorous birds accumulate DDT in their tissues, produce brittle egg shells .