Ecological Science

An understanding of ecology is fundamental to managing Earth’s resources. Ecology depends on information and principles developed in physiological, evolutionary, population and community ecology.

The term Ecosystem refers to life in all its forms, and the natural processes that support and connect all life forms. Ecosystems consists of all the organisms and abiotic (non-living: water, sunlight, air, minerals) components with which they interact. An ecosystem is a dynamic complex of plant, animal and microorganism communities all interacting as a functional unit, with non-living (abiotic) elements as affected by climate.

Many threads of ecological thought have contributed to the development of ecology. Changes in Earth systems have led to studies of the interactions among terrestrial ecosystems, the atmosphere and oceans. Ecological studies provide the mechanistic basis for understanding processes that occur at global scales using satellite-based remote sensing. Manipulation of ecosystems provides opportunities for comparisons. Comparative observations show many of the global patterns.

Ecosystem concepts provide a foundation for developing ecological principles.

Varieties of species live in different ecological zones. The variety of species living in each zone is largely determined by climate, the composition of soil and other substrate, as well as the legacy of species that have adapted to an area.

The impact of a species in an ecological zone depends on the abundance of the species in the geographical range that it occupies and the proportion of one species compared to other species.

Ecosystems are subjected to change as the social and physical components, and members change.

Components of Ecological Systems

Ecosystem structure and functioning have many components.

Climate

Climate is a major energy component in an ecosystem and indicates the range of available sunlight, heat and rainfall. Plants capture solar energy in the process of bringing carbon into the ecosystem. Climate is affected by elevation, latitude and physical geography (mountains, lakes and oceans). Climate plays a large role in providing the environment suitable for a species. Different species require a temperature range or a different level of sunlight to operate at their optimum level.

Physical Geography

Structural and terrain components are the range of physical organizations and patterns of an ecological system, such as:

• mountains which affect rainfall and thus affect climate
• the physical structure of terrain: slope, soil and rock composition which govern drainage patterns
• rivers, streams and lakes are channelled by terrain and move water making it available to plants and animals

Terrain can affect habitat complexity, organizing habitats in patches.

Abiotic Components

Abiotic components are the substrate (soil and rock), and soil development. Substrate quality—soil and rock chemical composition—and the resulting nutrients (carbon, nitrogen and trace elements), acidity and fertility of the soil play a role in determining what species may live in a specific ecosystem. Some plants prefer an acidic environment to alkaline or vice versa. Likewise, species may favour sandy, loamy or clay soil.

Biotic (Biological) Components

The biotic components of ecosystems consist of living organisms: plants, animals and soil microorganisms (microbes are decomposers which break down dead organic material). The composition of an ecological system is identified by the list of species in an area which interact in a dynamic and sometimes stable relationship (stable state). Plants are a major habitat feature on land, they create food for insects and animals, herbivores, omnivores and carnivores.

Plant species differ in composition and the litter quality (ability to provide nutrients and improve or diminish soil quality) they generate. Low nutrient species decompose more slowly because of negative effects on soil microbes, reinforcing low nutrient availability. Species adapted to high-resource sites produce decomposing litter rapidly.

Composition is measured by the diversity of the species and gene pool in the area. Species information includes the identity and variety of species in an ecological system and describes its composition, richness and diversity.

Systems information describe the structure of an ecosystem such as ecological processes, predation, nutrient cycling and evolutionary processes such as gene flow, species relationships and mycorrhizal associations,

Herbivores, mainly insects and animals, move sugars and other nutrients up the food web and across the food web as they eat plants. Carnivores, also insects and animals, rely on other animals for their nutrients.

Human Intervention

Humans play a major role in which organisms are likely to succeed in an ecosystem. Factors such as pollution of waters and acid rain can alter the way an ecosystem operates. Farming, ranching, tree harvesting and urbanization reduce and change the nature of habitats.

The above components of ecological systems are the factors which determine which species which will occupy any biological community.

Ecological Concepts

Scale

The scale at which an ecological system is be examined depends on the questions asked by a study.

Small Scale

The scale of a study may examine life at small scale, for example genes are the working units of heredity; each gene is a segment of the DNA chromosome that encodes a single enzyme or structural protein unit. Genetic variation permits populations to adapt to changing environments and continue to participate in life’s processes.

Genes have impact on cellular structure. Physiological processes affect the life history of leaves.

Questions about biotic processes can be asked at both the chemical and cellular level.

Species Scale

Species are a complete, self-generating, unique ensemble of genetic variation, capable of interbreeding and producing fertile offspring. Species interaction describes competition between plant species in a clump or gap that affect populations, disturbance and predation processes, and that influences the composition and structure of a community.

Large Scale

A study may examine life at a large scale. For example, studies at a large scale may examine disturbance and predation processes that influence the composition and structure of a community. Studies at a large scale may examine the impact of processes on large geographical features such as forests, ecological zones, multiple ecological zones or may examine the global picture.

Filters

Ecosystem management concepts use both coarse and fine filter analysis.

The ‘coarse filter’ approach refers to the management of landscapes through a network of protected areas and their buffer zone that attempts to emulate and conserve natural ecological processes within a natural range of variability.

‘Fine filter’ studies approach the management of biodiversity at the species level through an individual or localized perspective when species issues are not effectively addressed by the coarse filter approach. Individual species sometimes require special attention, sometimes in localized areas.

Processes and interaction of species at each level study patterns. The process of relating these patterns is referred to as a panarchy.

The time scale of observations of ecological processes may also vary, ranging from minutes to millennia.

Studies can relate any and all of the coarse and fine filter, small scale large scale, short and long time scales.

Keystone Species

Keystone species are species that have disproportionately large effects on ecosystems and landscapes, typically because they alter critical slow variables. A keystone species is ecologically distinct from all other species in the ecosystem. The loss or reintroduction of a keystone species has a broad impact on the ecosystem.

Examples of Keystone Species

Species that modify disturbance regime exert strong effects on ecosystem functioning.

Ecosystem engineers such as beavers play a role in altering the hydrological characteristics of streams and wetlands. Earthworms and termites mix soil, altering soil development in a number of ways.

Species may tap unused resources making them available. Some deep-rooted species increase the supply of water by accessing deeper water supplies thus enhancing ecosystem productivity. Fungi may make nutrients more available. Highly mobile animals such as salmon and sheep, act as keystone species governing nutrient supply by feeding in one place and dying or defecating somewhere else. Migrating salmon bring in nutrients from the sea. Species that influence the supply of growth-limiting resources generally have large effects on the functioning of ecosystems.

In an old growth forest, the trees themselves are the keystone species, sustaining the ecosystem. Remove the trees and the wildlife, fungi, ferns and bryophytes (moss, etc.) are displaced.

Keystone species may have impact on biogeochemistry. Nitrogen-fixers affect the availability of nitrogen (a nutrient) and have a larger impact where there is low nitrogen supply. Lack of resident nitrogen-fixing species or preferential grazing on nitrogen-fixing species can affect the availability of nutrients for other plants.

Impact of Removal : Reintroduction

When otters are removed from the sea, other populations can explode—ie., sea urchins which then eat the kelp which provides physical structure for diverse subtidal communities. Removal of kelp can lead to coastal erosion. Removal of wolves releases elk populations that overgraze willow which leads to stream erosion. Loss of insectivores can result in an influx of nuisance insects. Removal of elephants leads to encroachment of woody plants on savannas.

Introduction of plant species without their host insect herbivores or pathogens can lead to a species becoming an aggressive invader.

Keystone Ecosystems

Keystone ecosystem are particularly important because they provide habitat for critical elements or a large portion of an area’s biodiversity that maintains balance in a system. For example, riparian ecosystems near streams, lakes and wetlands are considered keystone since they cover a relatively small area, yet support a disproportionately large number of species. These ecosystems have a positive impact on the landscape and provide/distribute many services to their inhabitants. They sustain natural ecosystem process and scarce resources.

Keystone processes

Keystone processes are fundamental to the maintenance of an ecosystem. For  example, fire plays a vital role in maintaining open ponderosa pine forests and grasslands in B.C.’s dry interior.

Some hardwood trees in the rainforests that are our most effective above-ground carbon sinks are also the product of the relationship between seeds and the fruit-eating animals that eat them. Some trees are up to 500 times more likely to germinate when the seeds have first passed through the digestion system of a bat, monkey or elephant.

Ecosystem Dynamics

Systems Theory: the importance of a systems approach

An ecological community is like an organism, made of interacting parts. Ecosystems are affected by natural cycles and processes. Elements of the community and cycles interact in important ways and cannot be understood in isolation. Understanding the patterns assists the understanding of how ecosystems function. Factors such as the productivity of vegetation strongly influences the cycling rates of materials. An understanding of the disturbance-succession cycle leads to an understanding of directional change in ecosystem structure and functions, and the mechanisms responsible for vegetative change.

Biotic system dynamics examines species and their interactions.

Ecosystem dynamics are a product of many variables: variations in conditions—cool or warm, wet or dry, availability of resources (fertile or unfertile) and changes in frequency of disturbances. Examples of biotic species dynamics:

• Boreal mosses form thick mats that insulate the soil, retarding decomposition, contributing to slow nutrient cycling.
• Sequestration of nitrogen and phosphorus in undecomposed peat reduces growth of vascular plants.
• Forests influence regional climates.
• Rough canopies generate mechanical turbulence, allowing eddies of air to penetrate deep within the plant canopy.

Availability of Resources

The availability of nutrients, the supply of water and minerals from soils to plants depends not only on the activities of soil microbes but also on physical and chemical interactions among rocks, soils and the atmosphere. In more detail, dynamics depend on:

• global budgets of materials that cycle between the atmosphere, land and water
• the weathering of rocks
• precipitation
• the dissolution of materials in water
• the decomposition of dead biomass
• the availability of resulting products in the food chain

The unavailability of essential elements constrains plant growth.

Feedback Loops

Feedback loops regulate the internal dynamics of ecosystems. There are two types of feedback loops—stabilizing and amplifying.

Stabilizing feedback loops occur when two changes to a system have opposite effects. Stabilizing loops provide resistance to change, reduce the risks of large scale spread of disturbances and constrain community productivity.

Amplifying feedbacks lead to state changes (population extinctions and population expansions) until other limiting factors come into play.

Anticipating the Effect of Traits on Ecosystems

Traits of organisms are the product of their evolutionary histories—the competitive environments in which they developed. Traits sort species into communities where they successfully grow and reproduce.

The impact of a given species on an ecosystem depends on the characteristics of that species. Organisms affect ecosystems in multiple ways because they have different traits such as competitiveness, hardiness and toxicity.

The effect many species have on an ecosystem are often indirect and not easily predicted. For example, a species may be more persistent because of an effective seed distribution system.

Theoretical frameworks for predicting the types and nature of interactions are only beginning to emerge.

System States

Ecosystems or landscapes are in steady state if there is no long-term directional trend in their properties or in the balance between inputs and outputs. Ecosystems are most likely to sustain their current properties if current keystone species (or their functional equivalents) are maintained and new ones are not introduced.

Natural Range of Variability

The term ‘natural range of variability’ (NRV) is used to describe naturally occurring variation over time of the composition and structure found in an ecological zone, resulting in part from sequences of disturbances. Baselines are established by examining the variations that occurred during prior centuries. The longer the time frame over which the variability is calculated, the more variability is included in the base line.

Infrequent catastrophic events are sometimes excluded from the NRV estimates.

If key attributes of ecosystems and landscapes are managed within the natural range of variability, the species associated with those ecosystems and landscapes can be maintained.

Current trends

• Species loss is occurring more rapidly than migration or evolution can maintain diversity. As plants and animals go extinct, the variety of animals left is constantly diminishing.
• Climate change will play an important role estimating the current and future natural ranges.

Change Rates

The rates of ecosystem processes are constantly changing due to:

• changes in seasons (light, heat, humidity)
• changes to climate
• availability of nutrients
• activities of organisms on time scales
• changes to salinity of the oceans
• contamination of land, water and the atmosphere

Energy : Photosynthesis : Carbon Production

Most plants, algae and cyanobacteria perform photosynthesis. Photosynthesis is the process by which most carbon and chemical energy enter ecosystems.

Plants use solar energy to reduce CO2 to organic matter, most of which ages, dies and directly enters the soil where it is decomposed by bacteria and fungi. In the process of photosynthesis, plant respiration converts carbohydrates to CO2 and water, releasing energy that can be used for growth and maintenance. The process always begins when energy from light is absorbed by proteins, called reaction centers, that contain green chlorophyll (and other coloured) pigments. In the light-harvesting reactions, chlorophyll (a light absorbing pigment) fixes energy from visible light, producing sugars which are distributed to the plant for storage and to support growth of roots, stems, trunks and leaves.

Plant photosynthesis provides the carbon and energy that drive most biological processes in ecosystems. Carbon is the main element that plants produce. Energy fixed by photosynthesis directly supports plant growth and produces organic matter that is consumed by animals and soil microbes. The carbon derived from photosynthesis makes up about half the organic matter on earth, hydrogen and oxygen account for most of the rest.

Photosynthesis is performed differently by different species. The energy content of organic matter varies among carbon compounds produced by a organism.

Factors that Affect the Productivity of a Plant

Photosynthesis depends on

• the availability of soil resources (water and nutrients)
• climate and time since disturbance
• the carbon-fixation capacity of the plant (or light-independent reactions) to convert CO2 into sugars— a more permanent form of chemical energy that can be stored, transported and metabolized
• the location of the plant’s leaves in a forest or plant canopy—the availability of soil resources, especially water and nutrient supply is critical.

Phosphorous limits the productivity of many lakes. Phosphorus pollution is responsible for algal blooms.

Cycles and Processes

Carbon Cycles

The ‘Carbon Cycle’ refers to the continuous movement of carbon derived from the Earth’s natural environment (land and water) through the atmosphere and living organisms. Carbon flows among Earth’s systems including terrestrial, atmospheric and oceanic systems. Biological growth captures carbon dioxide (CO2) from the atmosphere and distributes the carbon within the terrestrial land ecosystem. This process is highly important to all life on Earth.

Carbon Cycle 1

Photosynthesis breaks CO2 down into oxygen and carbon removing carbon from the atmosphere and stores carbon in sugars, cellulose and other organic material.

In the next stage carbon and oxygen combine to form CO2 through respiration and other processes after it is consumed by animal and microorganisms or burned as fuel releasing carbon back into the atmosphere continuing the cycle. Respiration is a biochemical process that converts carbohydrates back into CO2, and water releasing energy that can be used for growth and maintenance of other organisms.

See also Decomposition

Carbon Cycle 2

Coral reefs form through a combination of carbon, calcium and oxygen which can become rock in the form of limestone and marble, taking carbon out of the oceans and sequestering it in reefs. Coral reefs are the building blocks of limestone. When limestone comes under heat and pressure in the Earth’s crust, it turns to marble.

Acidic water dissolves limestone and marble. The manufacture of cement releases CO2 in the atmosphere when calcium carbonate is heated, producing lime or cement and carbon dioxide.

The Impact of Human Activity

Increased human activity is upsetting the carbon cycle balance. Humans are releasing more carbon into the atmosphere than Earth’s natural carbon sinks can absorb. The continuous burning of fossil fuels for energy and production of concrete results in billions of tonnes of carbon and other greenhouse gas emissions which are released into the atmosphere daily.

Carbon Sinks

Carbon is stored in carbon sinks. A carbon sink is anything that absorbs more carbon from the atmosphere than it releases. Examples of carbon sinks are the carbon that is stored in plants and their roots, in bogs, stored underground in fossil fuels (coal, gas and oil) and stored in coral reefs, limestone and marble.

Storage of carbon in carbon sinks and preservation of carbon sinks is critical to the slowing and reversal of climate change—to Earth’s future.

Carbon Source

A carbon source is anything that releases more carbon into the atmosphere than it absorbs, such as the burning of fossil fuels and the manufacture of cement.

The Water Cycle

Water is utilized by organisms and is transpired into the atmosphere by these organisms. Water evaporates into the atmosphere from rivers, lakes and oceans. Transpiration is tightly linked to the capacity of plants to fix carbon and therefore to their productive potential. Evaporation purifies water and the winds distribute evaporated water.

Precipitation releases water from the atmosphere to the Earth and oceans in the form of rain or snow. In cold climates and at Earth’s north and south poles, water has been stored as ice and snow. With global warming glaciers are melting.

The Nutrient Cycle : Trophic Dynamics

Trophic: pertaining to food or nourishment

Trophic dynamics describe the movement of carbon nutrients and energy among organisms in the ecosystem and the factors that regulate the carbon cycle through plants and ecosystems.

Ecosystem Paths

Plants, animals and microorganisms transfer energy and materials (carbon, water and mineral elements) as organisms feeding on other live organisms and on decaying material from dead organisms through predation, decomposition and micrology. Carbon in the form of sugars cellulose and fat is transferred between organisms in the food web.

Water moves in the atmosphere, across land and in oceans interacting with the atmosphere, substrate and organisms.

Transfers

Transfers involve the feeding relationships among organisms and the exchange of materials between organisms and their environment.

Most nutrient transfers in ecosystems involve absorption of nutrients by plants and the creation of sugars, ending with return to the soil as dead organic matter from which nutrients are released by microbial breakdown. Other nutrient transfers involve the movement of nutrients from plants to herbivores, omnivores and carnivores.

The flow or movement of resources (carbon oxygen, nitrogen and trace elements) and nutrients (sugars and fats) through ecosystems depends, in part, on the physiological properties of plants, animals and soil microbes.

Trophic Levels

The nutrient cycle is the transfers of energy and materials from one pool to another, between soil, vegetation, consumers and decomposers and back to soil.

The First Trophic Level : Plants  (primary production)

Energy enters the ecosystem when energy (light and heat), carbon dioxide and other materials are synthesized into sugars by photosynthesis. The availability of food at the first trophic level is influenced by the availability of water and the concentrations of nitrogen, phosphorous and other trace elements. Primary production of vegetation is more abundant in fertile environments.

The Second Trophic Level : Insects and Herbivores

Some birds, animals and insects are herbivores, eating only vegetation material. Some herbivores are specialists in what they eat. Feeding is influenced by the defensive compounds of plants.

Herbivore biomass and production tends to increase with increasing primary production. Plants in fertile environments are often well adapted to herbivory. Herbivore feeding speeds the turnover (cycling) of biomass. Higher grazing can reduce plant cover and increase erosion.

The Third Trophic Level : Predators – Omnivores and Carnivores

Some birds, animals and insects are omnivores—eating vegetation, insects, birds and other animals. Some birds, animals and insects are carnivores, eating mostly carrion.

Predators regulate the abundance of their prey. The productivity of organisms at the second trophic level constrains the quantity of predators at the third level.

Controls : Trophic Effects on Nutrient Cycling

The properties of a species, determines what it eats and is eaten by, and its role (niche) in the ecological community. The balance of nitrogen, phosphorous and digestible energy influence the efficiency with which plants support animal production. The presence of plant, animal and microbial species and their densities, are determined by the abundance of food, rates of resource consumption, predation, disturbances, age and composition of an ecosystem. Controls over consumption efficiency can be described in terms of the factors affecting the rate of energy transfers (the activity budget of organisms). Activities on the organism’s agenda include time spent locating food, eating (ingesting), digesting, reproducing, sleeping and avoiding predators.

Consumption by predators alters the abundance of organisms. Predators eat more selectively as more food becomes available.

The Food Web

The food web consists of the organisms in an ecosystem linked together by consumption patterns. Webs are complex. Nutrients and energy move up, down and across trophic levels (across the food web). The metaphor of a food chains with the flow of nutrients moving up the chain is an oversimplification.