Ecological Succession and Productivity in Ecosystems

Succession

The process by which the species composition of a community changes over time.

Seral stage

Each stage of community changes during the process of succession.

Pioneer species

The earliest species to arrive at a site.

Importance of pioneer species

They initiate ecological succession in barren environments, essential for soil formation, nutrient cycling, and habitat creation.

Examples of pioneer species

Lichen and moss.

Climax community

The final stage in the process of succession.

Measuring succession

By observing the change in species diversity over time.

Cronosequence

A sequence of communities that exist over time at a given location.

Primary succession

The development of communities in habitats that are initially devoid of plants and organic soil, such as sand dunes, lava flows, and bare rock.

Causes of primary succession

When a new patch of land is created/exposed for the first time.

Secondary succession

The development of communities in habitats that have been disturbed and include no plants but still contain organic soil.

Causes of secondary succession

Disturbances such as fire, flooding, windstorms, and human activities (e.g. deforestation).

Animal succession

In response to changes in the habitat, a species that lives in the community change as well.

Intertidal succession

The process by which an intertidal community develops and changes over time as different species colonize and replace each other.

Impact of succession on species richness

Succession is associated with a rapid increase in species richness that slows over time and eventually plateaus.

Facilitation

A mechanism of succession in which the presence of one species increases the probability that a second species can become established.

Examples of facilitation

Pioneer species such as lichen, moss, legumes.

Inhibition

A mechanism of succession in which one species decreases the probability that a second species will become established.

Examples of inhibition

Bryozoans (colonize rocks first and prevent colonization of sponges by competing for space on rocks).

Priority effect

When the arrival of one species at a site affects the subsequent colonization of other species.

Tolerance

A mechanism of succession in which the probability that a species can become established depends on its dispersal ability and its ability to persist under the physical conditions of the environment.

Benefits of tolerance

Tolerance is beneficial in ecology because it helps species survive harsh or changing conditions, supports biodiversity, aids in ecosystem recovery, and reduces competition—making ecosystems more stable and resilient.

Permanent climax community

No, succession tends toward stability, but dynamic ecosystems and external factors often prevent a single, unchanging climax from forming.

Transient climax community

A climax community that is not persistent.

Gaps in the climax community

This allows for large amounts of light to reach the forest floor and favors the growth of species from earlier seral stages.

Community stability

The ability of a community to maintain a particular structure.

Resilience and resistance

Concepts related to community stability.

Community resilience

the time it takes after a disturbance for a community to return to its original state

Community resistance

the amount that a community changes when acted upon by some disturbance, such as the addition/removal of a species

Alternative stable state

When a community is disturbed so much that the species composition and relative abundance of populations in the community change, and the new community structure is resistant to further change

Importance of fire in ecosystems

Fire is important because it doesn't kill all trees and can help in seed dispersal.

Fire-maintained climate community

A successional stage that persists as the final seral stage due to periodic fires.

Grazer-maintained climax community

When a successional stage persists as the final seral stage due to intense grazing.

Primary succession

The first plant species to colonize an area are generally lichens and mosses.

Seral stage

Each stage of community change in succession.

Common pattern of change in species richness during succession

Increase → plateau → decline

Standing Crop

A method of estimating productivity.

Gross Primary Productivity (GPP)

A method of estimating productivity.

Net Primary Productivity (NPP)

NPP = GPP - Maintenance (the energy required to keep the plant alive).

How primary productivity provides energy to the ecosystem

1) The change in the biomass of producers over time 2) The movement of carbon dioxide over time 3) The movement of oxygen over time.

Productivity in terrestrial ecosystems

Tropical rainforests are the most productive, whereas deserts are the least productive.

Productivity in aquatic ecosystems

Swamps, marshes, and coral reefs are the most productive, whereas the open ocean is the least productive.

Factors influencing energy transfer efficiency

Consumption/digestion, portion of energy that a consumer digests and absorbs, energy used for respiration, reproduction or growth, and energy residence time.

Primary productivity

The rate at which solar or chemical energy is captured and converted into chemical bonds by photosynthesis or chemosynthesis.

Standing crop

The biomass of producers present in a given area of an ecosystem at a particular moment in time.

Gross primary productivity (GPP)

The rate at which energy is captured and assimilated by producers in a given area (measured in J or kJ).

Net primary productivity (NPP)

The rate energy is assimilated by producers and converted into producer biomass in a given area.

Remote sensing

A technique measuring conditions on Earth from a distant location, typically using satellites or airplanes that take photographs of large areas of the globe.

Green Food Web

A food web focused on how the producers obtain energy from photosynthesis (or chemosynthesis) and how this energy moves up the food web when producers are consumed.

Brown Food Web

A food web focused on how scavengers, detritivores, and decomposers obtain energy from dead organic matter and how this energy moves up the food web when they are consumed.

Scavengers

Organisms that consume dead animals.

Detritivores

Organisms that break down dead organic matter and waste products into smaller particles.

Decomposers

Organisms that break down organic matter into simpler elements and compounds that are then recycled through the ecosystem.

Egested energy

The portion of consumed energy that is excreted or regurgitated.

Assimilated energy

The portion of energy that a consumer digests and absorbs.

Respired energy

The portion of assimilated energy a consumer uses for respiration.

Net secondary productivity

The rate of consumer biomass accumulation in a given area.

Trophic pyramid

A chart composed of stacked rectangles representing the amount of energy or biomass in each trophic group.

Pyramid of energy

A trophic pyramid that displays the total energy existing at each trophic level.

Pyramid of biomass

A trophic pyramid that represents the standing crop of organisms present in different trophic groups.

Consumption efficiency

The percentage of energy or biomass in a trophic level that is consumed by the next higher trophic level.

Assimilation efficiency

The percentage of consumed energy that is assimilated.

Net production efficiency

The percentage of assimilated energy that is used for growth and reproduction.

Ecological efficiency

The percentage of net production from one trophic level, compared to the next lower trophic level; also known as food chain efficiency (Rule of thumb = 10%).

Energy residence time

The length of time that energy remains in a given trophic level.

Ecological stoichiometry

The study of the balance of nutrients in ecological interactions, such as between an herbivore and a plant.

Biomass residence time

The length of time that biomass remains in a given trophic level.

Dead zones

Low-oxygen areas in oceans/large lakes that are too low to support most marine life (hypoxia) mainly caused by human-driven nutrient pollution.

Eutrophication

An increase in the productivity of aquatic ecosystems.

Cultural Eutrophication

An increase in the productivity of aquatic ecosystems caused by human activities.

Carbon cycle

A cycle where producers take up CO2 from the atmosphere and the water, transfer assimilated carbon to consumers, detritivores, scavengers, and decomposers, which return CO2 to the atmosphere and oceans through respiration.

Phosphorus cycle

A cycle where phosphate rocks that are uplifted by geologic forces naturally weather over time to release phosphorus.

Human alteration of the carbon cycle

CO2 emissions from transportation, deforestation, burning of fossil fuels.

Phosphorus

These rocks are the source of phosphorus used in fertilizer and detergents.

Phosphorous uptake

Phosphorous is taken up by producers and moves through the food chain until it is released either through waste or decomposition.

Excess Phosphorous runoff

Excess Phosphorous on land runs off the surface / leaches out of the soil and into aquatic habitats.

Phosphorous precipitation

In the ocean, phosphorous combines with calcium / iron and precipitates out of the water, forming phosphate rocks again.

Human alteration of phosphorus cycle

By using fertilizers, mining phosphate, sewage, and causing erosion, which leads to excess phosphorous in water and causes algal blooms, dead zones, and ecosystem damage.

Hydrologic cycle

The movement of water through ecosystems and atmosphere.

Solar energy in hydrologic cycle

Solar energy drives the movement of water by evaporating it from soil and water bodies, also evapotranspiration from plants.

Precipitation in hydrologic cycle

Evaporated water returns to Earth as precipitation.

Infiltration and runoff

The precipitation either infiltrates the soil or flows along the surface of the ground until it enters streams / rivers.

Water uptake by plants

Water in the soil is taken up by plants or enters the groundwater. Ultimately, water returns to the ocean.

Impact of logging on hydrologic cycle

When forests are logged, fewer plant roots are available to hold soil, and the soil absorbs less rainwater; this causes increased surface runoff, more severe floods, and large amounts of soil.

Ogallala Aquifer

Largest source of groundwater in the US, but the extraction exceeds replenishment.

Nitrogen cycle

The nitrogen cycle begins with nitrogen gas in the atmosphere.

Nitrogen fixation

The process of nitrogen fixation converts atmospheric nitrogen into a form that producers can use.

Assimilation in nitrogen cycle

The fixed nitrogen can then be assimilated into producers and consumers; decomposes into ammonium through the process of mineralization.

Nitrification

The ammonium can be converted into nitrite and then nitrate through the process of nitrification.

Denitrification

Under anaerobic conditions, the nitrate can be converted into nitrogen gas through the process of denitrification.

Mutualistic relationships in nitrogen cycle

Legumes and Rhizobium bacteria, Frankia Bacteria and non-legume plants, and cyanobacteria and aquatic plants / fungi.

Ways to fix nitrogen

Nitrogen fixation: the process of converting atmospheric nitrogen to forms producers can use.

Haber-Bosch process

An industrial method used to produce ammonia (NH3) from nitrogen gas (N2) and hydrogen gas (H2) under high pressure and temperature, using an iron catalyst.

Watershed

An area of land that drains into a single stream or river.

Source of fossil fuels

Carbon from plants that were trapped in soil millions of years ago.

Studying historical CO2 levels

Using ice cores from glaciers that contain small amounts of air trapped for hundreds of thousands of years.