Ecologists study how organisms interact with their environment at several levels Individual organisms interacting with the environment Population Group of individuals of the same species living in a particular geographic area

Community All the populations of different species that inhabit a particular area Ecosystem All the biotic and abiotic components in a certain area Ecological research is conducted in the field as well as in the lab and with models

THE BIOSPHERE The biosphere is the total of all of Earth's ecosystems The biosphere is the global ecosystem Atmosphere to an altitude of several kilometers Land down to 3,000 m beneath Earth's surface Oceans to a depth of several kilometers The biosphere is self-contained and characterized by patchiness

Environmental problems reveal the limits of the biosphere Current awareness of the biosphere's limits stems from past environmental practices Rachel Carson warned of the effects of pesticides in 1962

Physical and chemical factors influence life in the biosphere Major abiotic factors determine the biosphere's structure and dynamics Solar energy Water Temperature Wind Disturbances such as fire, tornadoes

Organisms are adapted to abiotic and biotic factors by natural selection Species exist in a given place because they evolve there or disperse there Unique adaptations that fit a particular environment allow organisms to survive there Example: pronghorns Organisms vary in their ability to tolerate changes in their environment

STRUCTURAL FEATURES OF COMMUNITIES Key characteristics of a community Species diversity: variety of different kinds of organisms Species richness Relative abundance

Dominant species Response to disturbances Trophic structure: feeding relationships among species

Competition may occur when a shared resource is limited Interspecific competition may play a major role in structuring a community 2 species competing for the same limited resource May inhibit growth of one or both species

Competitive exclusion principle 2 species cannot coexist in a community if their niches are identical Niche: species' total use of biotic and abiotic resources 2 possible results Less competitive species will be driven to local extinction Resource partitioning may evolve

LE 37-2a

LE 37-2b

Video: Seahorse Camouflage Predation leads to diverse adaptations in both predator and prey Predation is an interaction between species in which predator kills and eats prey Adaptations of both tend to be refined through natural selection Camouflage Chemical defense Video: Seahorse Camouflage

Batesian mimicry Mullerian mimicry Palatable species mimics an unpalatable model Mullerian mimicry Two unpalatable species mimic each other

Predation can maintain diversity in a community Keystone species Exerts strong control on community structure because of its ecological niche Keystone predator May maintain community diversity by reducing numbers of the strongest competitors Removal can cause major changes in community dynamics

Herbivores and the plants they eat have various adaptations Herbivores are animals that eat plants or algae Have adaptations for locating and eating vegetation Plants have evolved defenses against herbivores Toxic chemicals Physical defenses (spines, thorns)

Some herbivore-plant interactions illustrate coevolution Reciprocal evolutionary adaptations Change in one species acts as a new selective force on another species

LE 37-5 Eggs Sugar deposits

Symbiotic relationships help structure communities Symbiotic relationship: interaction between two or more species that live in direct contact Parasitism Parasite lives on or near its host Parasite obtains nourishment at the expense of host Includes pathogens that may inflict lethal harm on host

Commensalism Mutualism One species benefits without significantly affecting the other Few absolute cases documented Mutualism Both partners benefit

Disturbance is a prominent feature of most communities Disturbances are characteristic of most biological communities Events such as fire, storms, floods Damage communities Remove organisms from communities Alter the availability of resources Can have positive effects

Ecological succession is a transition in community species composition following a major disturbance Primary succession: gradual colonization of barren rocks Secondary succession: occurs after a disturbance has destroyed a community but left the soil intact

LE 37-7 Retreating glacier with moraine in the foreground Dryas stage Spruce starting to appear in the alder and cottonwood forest Spruce and hemlock forest

Trophic structure is a key factor in community dynamics Trophic structure: a pattern of feeding relationships consisting of several different levels Food chain: sequence of food transfer up the trophic levels Moves chemical nutrients and energy

Producers Primary consumers Autotrophs that support all other trophic levels Plants on land In water, mainly photosynthetic protists and cyanobacteria Primary consumers Herbivores that eat plants, algae, or phytoplankton

Video: Shark Eating Seal Secondary, tertiary, and quaternary consumers Eat consumers from the level below them Detritivores (decomposers) Animal scavengers, fungi, and prokaryotes Derive energy from detritus produced at all trophic levels Decomposition is essential for recycling nutrients in ecosystems Video: Shark Eating Seal

A terrestrial food chain LE 37-9 Trophic level Quaternary consumers Hawk Killer whale Tertiary consumers Snake Tuna Secondary consumers Mouse Herring Primary consumers Grasshopper Zooplankton Producers Plant Phytoplankton A terrestrial food chain An aquatic food chain

Food chains interconnect, forming food webs A food web is a more realistic view of trophic structure Consumers usually eat more than one type of food Each food type is consumed by more than one type of consumer

LE 37-10 Quaternary, tertiary, and secondary consumers Tertiary and primary consumers Primary consumers Producers (plants)

Chemical cycling Chemical energy Heat energy Chemical elements flow Chemical energy Light energy Heat energy Chemical elements

Primary production sets the energy budget for ecosystems Primary production: amount of solar energy converted by producers to chemical energy in biomass Biomass: amount of organic material in an ecosystem Net primary production: amount of biomass produced minus amount used by producers in cellular respiration Varies greatly among ecosystems

Average net primary productivity (g/m2/yr) LE 37-12 Open ocean Estuary Algal beds and coral reefs Desert and semidesert scrub Tundra Temperate grassland Cultivated land Boreal forest (taiga) Savanna Temperate deciduous forest Tropical rain forest 500 1,000 1,500 2,000 2,500 Average net primary productivity (g/m2/yr)

Energy supply limits the length of food chains Only about 10% of the energy stored at each trophic level is available to the next level Pyramid of production shows loss of energy from producers to higher trophic levels Amount of energy available to top-level consumers is relatively small Most food chains have only three to five levels

Tertiary consumers Secondary consumers Primary consumers Producers LE 37-13 Tertiary consumers 10 kcal Secondary consumers 100 kcal Primary consumers 1,000 kcal Producers 10,000 kcal 1,000,000 kcal of sunlight

A production pyramid explains why meat is a luxury for humans Human meat or fish eaters are tertiary or quaternary consumers Humans eating grain have ten times more energy available than when they process the same amount of grain through meat Using land to raise animals consumes more resources than using the land to cultivate crops

Trophic level Secondary consumers Human meat-eaters Primary consumers vegetarians Cattle Corn Corn Producers

Biogeochemical cycles Cycle nutrients through both biotic and abiotic components Can be local or global

Consumers Producers Detritivores Nutrients available to producers Abiotic reservoir

Water moves through the biosphere in a global cycle Solar energy drives the global water cycle Precipitation Evaporation Transpiration Water cycles between the land, oceans, and atmosphere Forest destruction and irrigation affect the water cycle

Transport over land Solar energy Net movement of water vapor by wind LE 37-16 Transport over land Solar energy Net movement of water vapor by wind Precipitation over land Precipitation over ocean Evaporation from ocean Evaporation and transpiration from land Percolation through soil Runoff and groundwater

The carbon cycle depends on photosynthesis and respiration Carbon cycles through the atmosphere, fossil fuels, and dissolved carbon in oceans Taken from the atmosphere by photosynthesis Used to make organic molecules Decomposed by detritivores Returned to the atmosphere by cellular respiration Burning of wood and fossil fuels is raising the level of CO2 in the atmosphere

CO2 in atmosphere Photosynthesis Cellular respiration Burning of LE 37-17 CO2 in atmosphere Photosynthesis Cellular respiration Burning of fossil fuels and wood Higher-level consumers Primary consumers Carbon compounds in water Detritus Decomposition

The nitrogen cycle relies heavily on bacteria Atmospheric N2 is not available to plants Soil bacteria convert gaseous N2 to usable ammonium (NH4+) and nitrate (NO3-) Some NH4+ and NO3- are made by chemical reactions in the atmosphere Human activity is altering nitrogen cycle balance in many areas Sewage treatment and fertilization

Nitrogen in atmosphere (N2) LE 37-18 Nitrogen in atmosphere (N2) Nitrogen fixation Assimilation by plants Denitrifying bacteria Nitrogen-fixing bacteria in root nodules of legumes Nitrates (NO3–) Detritivores Decomposition Nitrifying bacteria Ammonium (NH4) Nitrogen-fixing soil bacteria

The phosphorus cycle depends on the weathering of rock Phosphorus and other soil minerals are recycled locally Weathering of rock adds PO43- to soil Slow process makes amount of phosphorus available to plants low Human activity has created phosphate pollution of water

Rain Geologic Weathering uplift of rocks of rocks Plants Runoff LE 37-19ECOSYSTEM Rain Geologic uplift of rocks Weathering of rocks Plants Runoff Consumption Sedimentation Plant uptake of PO43– Soil Leaching Decomposition