Ecosystem Ecology

I. Ecosystems A. Definition 1. An ecosystem is an association of organisms and their physical environment, 2. Linked by a flow of energy and a cycling of materials.

B. Structure of Ecosystems 1. Physiognomic structure a. Physical size & shape of organisms & their relation to each other & the physical environment b. Relative abundance of trees, shrubs, herbs, mosses, etc. c. Phenotypes, physical characteristics d. Vertical & horizontal stratification

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2. Temporal Structure a. Ecosystems change over time (succession) b. Diurnal (Daily) patterns c. Seasonal changes

3. Species Structure (Composition) a. Diversity, relative abundance b. Determined by soil resources, climate tolerance ranges, stresses (ex. Competitive interactions, herbivory)

II. Trophic levels A. Feeding levels 1. Autotrophs 2. Heterotrophs a. Plants, algae, cyanobacteria, phytoplankton b. Bring energy into the ecosystem by PSN c. First level of all food webs ---- primary producers 2. Heterotrophs a. consumers - depend directly or indirectly on energy stored in tissues of primary producers.

b. Types of Heterotrophs i. Herbivores eat plants – primary consumers ii. Parasites reside in or on living hosts iii. Detritivores consume dead or decomposing organic matter. iv. Carnivores – eat herbivores & other carnivores – secondary consumers v. Omnivores partake of a variety of edibles vi. Decomposers - extract energy and recycle nutrients from organic matter.

Decomposition intertwines all trophic levels. Fig 55.4

c. Complications i. Some organisms like man extract energy from more than one trophic level so it is hard to assign them to a specific trophic level. ii. Actual feeding relationships in an ecosystem are complex – more accurately described by food webs.

Fig 54.12

III. Bioenergetics A. Primary Production (PP) 1. Conditions a. Light = Amount of light energy converted to chemical energy (organic compounds) by an ecosystem’s autotrophs’ during a certain amount of time

2. Ecosystems differ in their PP: b. Efficiency = How much energy actually get stored depends on i. How many plants are present? ii. The balance between photosynthesis and aerobic respiration. 2. Ecosystems differ in their PP: a. Tropical rain forest – most per area b. Oceans – most overall

Fig 54.4

Fig 54.5

B. Gross primary productivity (GPP) 1. total amount of light energy converted to chemical energy per unit time

C. Net primary productivity 1. NPP = GPP – R 2. R = energy used by the primary producers for respiration. Energy released as heat. 3. Availability = The amount of stored chemical energy that will be available to the other trophic levels.

4. Losses of Net primary productivity a. Only a small part of the energy from sunlight becomes fixed in plants (1%). b. The plants themselves use as much as half of what they fix (respiration). c. Other organisms tap into the energy that is conserved in plant tissues, remains, or wastes. d. They lose heat to the environment.

e. All of these heat losses represent a one- way flow of energy out of the ecosystem.

D. Secondary Production 1. Amount of chemical energy from a consumer’s food that is converted into new biomass in their body. 2. Example Caterpillar eating a plant: a. 50% loss to feces (energy transfer to detritus) b. 34% to respiration (heat loss) c. 16% to growth

Fig 55.9

IV. Trophic efficiency A. Percentage of production transferred from one trophic level to the next. B. 5-20% depending on ecosystem. C. Thus 85-90% of available energy at one level is not transferred to the next. Instead lost as heat, not consumed, or transferred to detritus

Fig 55.11

Fig 55.11

Fig. 54.13

V. Biogeochemical Cycles A. Characteristics 1. Availability of inorganic material as well as energy profoundly influences the structure of ecosystems. 2. Cycling of nutrients involves biotic & abiotic components: “biogeochemical”

3. These are transferred from the environment to organisms and back again 4. Generally, these move slowly through the environmental reservoir, compared to its rapid exchange between organisms and the environment.

B. Reservoirs of Material 1. Available vs. Unavailable Organic a. Living & dead organisms – available through decomposition & consumption b. Fossil fuels: coal, oil, peat 2. Available vs. Unavailable Inorganic a. Molecules in air, soil, & dissolved in water b. Elements in solid rock

Fig 55.13

3. Characteristics of Material Reservoirs a. Elements used usually become available to producers as mineral ions, such as ammonium (NH4+). b. Inputs from the physical environment and the cycling activities of decomposers and detritivores maintain an ecosystem’s reserves. c. The amount being cycled through most major ecosystems is greater than the amount entering or leaving in a given year. d. Inputs to the reserves occur by rainfall or snowfall, metabolism, and weathering of rocks. e. Outputs for land ecosystems include losses by runoff.

Figure 55.14

Figure 55.14

Figure 55.14

Always move forward by building on the past.