Community. All the organisms of all the species inhabiting an area. Interspecific Interactions Competition: -/- Predation (includes herbivory and parasitism): +/- Mutualism: +/+ (obligatory or facultative= facilitation) Commensalism: +/0 Key in shaping communities: competition, predation and mutualism. The properties and structure of a community are defined by its species composition and the interactions between the species. Plant communities apparently determined by chance occurrence of species with similar requirements. Unclear in animal communities. Species interactions involved in determining trophic structure, dominant and keystone species, and community control. All affect community structure. Trophic structure. Feeding relationships between organisms. Food chain, trophic levels and food web. Food webs have few trophic levels: energetic and dynamic stability hypotheses.

Dominant species. Control in community due to abundance. Keystone species. Control in community due to ecological role. Community organization. Bottom-up model. Changes in community structure controlled by bottom trophic levels (competition and available food). Top-down model. Changes in community structure controlled by upper trophic levels (predation). Communities are dynamic, constantly changing, due to disturbance. Humans are the greatest agents of disturbance. Ecological succession- Transitions in species composition over ecological time. Primary succession- It begins in a virtually lifeless area where soil has yet not formed. Secondary succession- Occurs where an existing community has been cleared by some disturbance that leaves the soil intact.

1- Wouldn’t ash and other material be nutrient-rich and counted as soil, therefore making it secondary succession? Question from February 22nd

Chapter 54 Ecosystem Ecology

Organismal ecology coping Population ecology limiting factors Community ecology interspecific interactions and diversity Ecosystem ecology energy flow and chemical cycling Landscape ecology effects on interactions at lower levels Biosphere ecology global effects

Ecosystem. All the organisms living in a community AND the abiotic factors with which they interact. Ecosystem Ecology NASA page 1198 PaleoProject The most inclusive ecosystem is the biosphere or whole-Earth ecosystem.

(DECOMPOSERS) ECOSYSTEM DYNAMICS 1- Energy flows through ecosystems. 2- Matter cycles within ecosystems. Autotrophs Heterotrphs Tertiary consumers, etc. PHOTO, chemo All trophic levels are connected by decomposition. Without decomposition life on Earth would stop. 1 st Law of Thermodynamics Energy is conserved, it can only be transformed. 2 nd Law of Thermodynamics. Energy transformation is inefficient, some lost as heat. Elements are not lost, but move through trophic levels and ecosystems. pages Fig. 54.1

Primary Production. Light energy converted to chemical energy (organic compounds) by an ecosystem’s autotrophs in a given period of time (1% converted). Sets Ecosystem’s Energy Budget. ENERGY FLOW Energy per unit area per unit time (J/m 2 / yr) OR Biomass (dry weight) of organic molecule per unit area per unit time (gC/m 2 / yr). Fig pages

Gross Primary Production (GPP) = Total Primary Production (amount of light energy converted to chemical energy per unit time) Some used as fuel for cellular respiration, then: Net Primary Production (NPP) = GPP – R (as little as 25% of GP in forests) Only NPP is available to consumers. Ocean: 46%; Land: 54% Fig pages

Fig pages Fig Nutrition addition experiment

Detritivores Heat Fig Secondary Production Amount of chemical energy in consumer’s food converted to new chemical energy in a given period of time. Production efficiency= fraction of food energy that is not used for respiration. At individual level: page 1206

PE= 1-3% PE= 10%PE= 40%

~1% Trophic Efficiency Percentage of production transferred from one trophic level to the next. Values are 5-20% depending on ecosystem. Thus, 80-95% of energy is lost; loss is multiplied in each trophic level, forming a pyramid. ~10% Fig page 1206 Idealized pyramid of net production

Consequence of trophic efficiencies: total dry weight of all organisms (standing crop) diminishes with each successive trophic level. (pyramid of biomass). Some aquatic ecosystems have inverted pyramids. pages Fig Fig Predators usually larger than prey, so limited biomass in upper thropic levels formed by a small number of large individuals (pyramid of numbers).

Herbivores consume a small percentage of the plant biomass (globally, <17% of the annual plant production). page 1208 The green world hypothesis Several factors keep herbivores in check: -Plant defenses: toxins, spines, mutualistic invertebrates, etc. -Not all essential nutrients plenty available: organic nitrogen. -Abiotic factors limit herbivores. -Intraspecific competition: density-dependence. -Interspecific interactions: predation, parasitism and diseases.

Biological and geological processes move nutrients in the ecosystem. General model of nutrient cycling pages Fig Life on Earth depends on the recycling of essential chemical elements.

Water cycle is driven globally by solar energy. + + pages 1210 Fig

The Carbon cycle is defined by the reciprocal processes of photosynthesis and cellular respiration. balanced + pages 1210 Fig

Nitrogen enters ecosystem by atmospheric deposition and nitrogen fixation by prokaryotes. MOST of nitrogen cycling involves local processes between organisms and soil or water. pages Fig

Decomposition rates determine the rates of nutrient cycling. pages Fig Generalized scheme of biogeochemical cycles

Nutrient cycling is strongly regulated by vegetation. When plants are not present, nutrients are lost from the system. pages Fig

Bioscience 2005 Ecologists are recognizing the need of understanding how landscapes (comprise different ecosystems) and food webs interact. Gizzard shad Ohio reservoir