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Chapter 3Ecosystem Ecology

Ecosystem Ecology Examines Interactions Between the Living and

Non-Living World

• Ecosystem- A particular location on Earth distinguished by its particular mix of interacting biotic and abiotic components.

Ecosystem Boundaries

• Some ecosystems, such as a caves and lakes have very distinctive boundaries. However, in most ecosystems it is difficult to determine where one ecosystems stops and the next begins.

Ecosystem Processes

• Even though it is helpful to distinguish between two different ecosystems, ecosystems interact with other ecosystems.

Energy Flows through Ecosystems

Photosynthesis and Respiration

• Producers (autotrophs) are able to use the suns energy to produce usable energy through the process called photosynthesis.

Photosynthesis and Respiration

• Cellular respiration is the process by which other organisms gain energy from eating the tissues of producers.

Trophic Levels, Food Chains, and Food Webs

• Consumers (heterotrophs)- obtain energy by consuming other organisms.

• Primary Consumers (herbivores)- consume producers.

• Secondary Consumers (carnivores)- obtain their energy by eating primary consumers.

• Tertiary Consumers (carnivores)- eat secondary consumers.

• Food Chain- The sequence of consumption from producers through tertiary consumers.

• Food Web- A more realistic type of food chain that takes into account the complexity of nature.

Ecosystem Productivity

• Gross primary productivity (GPP)- The total amount of solar energy that the producers in an ecosystem capture via photosynthesis over a given amount of time.

• Net primary productivity (NPP)- The energy captured (GPP) minus the energy respired by producers.

Energy Transfer Efficiency and Trophic Pyramids

• Biomass- The energy in an ecosystem is measured in terms of biomass.

• Standing crop- The amount of biomass present in an ecosystem at a particular time.

• Ecological efficiency- The proportion of consumed energy that can be passed from one trophic level to another.

• Trophic pyramid- The representation of the distribution of biomass among trophic levels.

Matter cycles through the biosphere

• Biosphere- The combination of all ecosystems on Earth.

• Biogeochemical cycles- The movement of matter within and between ecosystems involving biological, geologic and chemical processes.

The Hydrologic Cycle

• The movement of water through the biosphere.

The Hydrologic Cycle

• Transpiration- The process where plants release water from their leaves into the atmosphere.

• Evapotranspiration- The combined amount of evaporation and transpiration.

• Runoff- When water moves across the land surface into streams and rivers, eventually reaching the ocean.

The Carbon Cycle

The Nitrogen Cycle

The Phosphorus Cycle

Ecosystems respond to disturbance

• Disturbance- An event caused by physical, chemical or biological agents that results in changes in population size or community composition.

Watershed Studies

• Watershed- All of the land in a given landscape that drains into a particular stream, river, lake or wetland.

Resistance versus Resilience

• Resistance- A measure of how much a disturbance can affect its flows of energy and matter.

• Resilience- The rate at which an ecosystem returns to its original state after a disturbance.

• Restoration ecology- A new scientific discipline that is interested in restoring damaged ecosystems.

The Intermediate Disturbance Hypothesis

• The intermediate disturbance hypothesis-states that ecosystems experiencing intermediate levels of disturbance are more diverse than those with high or low disturbance levels.

Ecosystems Provide Valuable Services

Instrumental Values of Ecosystems• Provisions- Goods that humans can use directly.

• Regulating services- The service provided by natural systems that helps regulate environmental conditions.

• Support systems- The support services that natural ecosystems provide such as pollination, natural filters and pest control.

• Resilience- Resilience of an ecosystem ensures that it will continue to provide benefits to humans. This greatly depends on species diversity.

• Cultural services- Ecosystems provide cultural or aesthetic benefits to many people.

Variations in Climate Determine the Dominant Plant Growth Forms of

Terrestrial Biomes

• Climate affects the distribution of species around the globe.

• Organisms possess distinct growth forms due to adaptations to local temperature and precipitin patterns.

• Biomes- The presence of similar plant growth forms in areas possessing similar temperature and precipitation patterns.

Tundra• Cold, treeless biome with low-growing

vegetation. In winter, the soil is completely frozen.

• The tundra's growing season is very short, usually only about 4 months during summer.

• The underlying subsoil, known as permafrost is an impermeable, permanently frozen layer that prevents water from draining and roots from penetrating.

Tundra

Boreal Forest

• Forests made up primarily of coniferous (cone-bearing) evergreen trees that can tolerate cold winters and short growing seasons.

• Boreal forests are found between about 50˚ and 60˚ N in Europe, Russia and North America.

• This subarctic biome has a very cold climate, and plant growth is more constrained by temperature than precipitation.

• The soil is nutrient-poor due to slow decomposition.

Boreal Forest

Temperate Rainforest• Moderate temperatures and high precipitation typify

the temperate rainforest.

• The temperate rainforest is a coast biome and can be found along the west coast of North America from northern California to Alaska, in southern Chile, on the west coast of New Zealand, and on the island of Tasmania.

• The ocean currents help moderate temperature fluctuations and provide a source of water vapor.

• This biome has a nearly 12-month growing season where winters are rainy and summers are foggy.

• The mild temperatures and high precipitation supports the growth of very large trees.

Temperate Rainforest

Temperate Seasonal Forest

• Receive over 1 m (39 inches) of precipitation annually.

• Found in the eastern United States, Japan, China, Europe, Chile and eastern Australia.

• Dominated by broadleaf deciduous trees such as beech, male, oak and hickory.

• Warmer summer temperatures favor decomposition so soils generally contain more nutrients than those of boreal forests.

Temperate Seasonal Forest

Woodland/Shrubland

• Found on the coast of southern California, southern Australia, southern Africa and in the area surrounding the Mediterranean Sea.

• Hot, dry summers and mild, rainy winters are characteristic of this biome.

• There is a 12-month growing season, but plant growth is constrained by low precipitin in summer and by relatively low temperatures in winter.

• Wildfires are common and plants of this biome are well adapted to both fire and drought.

Woodland/Shrubland

Temperate Grassland/Cold Desert• This biome has the lowest average annual

precipitation of any temperate biome.

• These are found in the Great Plains of North America, in South America, and in central Asia and eastern Europe.

• Cold, harsh winters and hot, dry, summers characterize this biome.

• Plant growth is constrained by both insufficient precipitation in summer and cold temperatures in winter.

• Plants include grasses and non woody flowering plants that are well adapted to wildfires and frequent grazing by animals.

Temperate Grassland/Cold Desert

Tropical Rainforest• In the tropics, average annual temperatures exceed

20˚C.

• This biome is located approximately 20˚ N and S of the equator.

• They are found in Central and South America, Africa, Southeast Asia, and northeastern Australia.

• Precipitation occurs frequently and this biome is warm and wet with little temperature variation.

• Tropical rain forests have more biodiversity per hectare than any other terrestrial biome and contain up to two-thirds of Earth's terrestrial species.

Tropical Rainforest

Tropical Seasonal Forest/Savanna• Warm temperatures and distinct wet and dry

seasons characterize this biome.

• Tropical seasonal forests are common in much of Central America, on the Atlantic coast of South America, in southern Asia, in northwestern Australia, and in sub-Saharan Africa.

• Soil in this biome is fairly fertile and can be farmed due to high decomposition rates, but the low amount of precipitation constrains plants from using the soil nutrients that are released.

• Grasses and scattered deciduous trees are common.

Tropical Seasonal Forest/Savanna

Subtropical Desert

• This biome is found at 30˚ N and S with hot temperatures and extremely dry conditions.

• The Mojave Desert in the southwestern United States, the Sahara in Africa, the Arabian Desert of the Middle East and the GReat Victoria Desert of Australia are all subtropical deserts.

• Cacti, euphorbs and succulent plants are well adapted to this biome.

Subtropical Desert

Chapter 6Population and Community Ecology

Nature exists at several levels of complexity

Factors that Regulate Population Abundance and Distribution

• Population size- the total number of individuals within a defined area at a given time.

• Population density- the number of individuals per unit area at a given time.

• Population distribution- how individuals are distributed with respect to one another.

• Population sex ratio- the ratio of males to females

• Population age structure- how many individuals fit into particular age categories.

Factors that Influence Population Size

• Density-dependent factors- the size of the population will influence an individual’s probability of survival.

• Density-independent factors- the size of the population has no effect on the individual’s probability of survival.

Exponential Growth Model

• Growth rate- the number of offspring an individual can produce in a given time period, minus the deaths of the individual or offspring during the same period.

• Intrinsic growth rate- under ideal conditions, with unlimited resources, the maximum potential for growth.

Exponential Growth Model

• J-shaped curve- when graphed the exponential growth model looks like this.

Logistic Growth Model

• Logistic growth- when a population whose growth is initially exponential, but slows as the population approaches the carrying capacity.

• S-shaped curve- when graphed the logistic growth model produces an “S”.

Variations of the Logistic Model

• If food becomes scarce, the population will experience an overshoot by becoming larger than the spring carrying capacity and will result in a die-off, or population crash.

Reproductive Strategies

• K-selected species- the population of a species that grows slowly until it reaches the carrying capacity. Ex. elephants, whales, and humans.

• R-selected species- the population of a species that grows quickly and is often followed by overshoots and die-offs. Ex. mosquitoes and dandelions

Survivorship Curves

Metapopulations

• Metapopulations- a group of spatially distinct populations that are connected by occasional movements of individuals between them.

Competition

• Competition- the struggle of individuals to obtain a limiting resource .

Resource Patitioning

Predation

• Predation- the use of one species as a resource by another species.

• True predators- kill their prey.

• Herbivores- consume plants as prey.

• Parasites- live on or in the organism they consume.

• Parasitoids- lay eggs inside other organisms.

Mutualism

• Mutualism- A type of interspecific interaction where both species benefit.

Commensalism• Commensalism- a type of relationship in which one

species benefits but the other is neither harmed nor helped.

Keystone Species

• Keystone species- a species that plays a role in its community that is far more important than its relative abundance might suggest.

Primary Succession• Primary succession- occurs on surfaces that are

initially devoid of soil.

Secondary Succession

• Secondary succession- occurs in areas that have been disturbed but have not lost their soil.

Aquatic Succession

Factors that determine species richness:

• Latitude

• Time

• Habitat size

Theory of Island Biogeography

• Theory of island biogeography- the theory that explains that both habitat size and distance determine species richness.