45:211: environmental geography ecosystems: ecological principles module 4

45:211: Environmental Geography

Ecosystems:Ecological Principles

Module 4


Agenda 21

• 7: States shall cooperate in a spirit of global partnership to conserve, protect and restore the health and integrity of the Earth's ecosystems. – Ecosystems are the productive engines of the

planet, providing us with everything from the water we drink, the food we eat and the fibre we use for clothing, paper, and lumber.


The fraying web of life

• Ecosystems can be damaged by:– Physical destruction - loss of habitat– Species decimation - loss of biodiversity– Intoxication - impacts of pollution and toxins– Damage to food webs

resulting in a decline in productivity


Outline• Ecosystem Concepts

• Connections, Integrity

• Habitat and Niche

• Bioregions

• Energy Flows Through Ecosystems• Energy pyramid

• Bioaccumulation

• Nutrient Cycles Through Ecosystems• Carbon cycle

• Toxins


Ecology

• Ecology: Study of how organisms interact with each other and with their non-living surroundings.


Biosphere

• Together:– biodiversity (the elements of life), and– ecological processes (the interactions between

species and their environment)

define Earth's living mantle - the biosphere.– Biodiversity - the number of different species in

an area


Bioregion

• A bioregion is a land and/or water territory whose limits are defined not by political boundaries, but by the geographical extent of ecological systems.


Ecosystem

• An ecosystem refers to all the living organisms and their physical environment within a given area. – the living component consists of the interacting

communities of animals, plants and microbes;– the non-living component refers to the air,

water, rocks, soil and climate.


Ecosystems are everywhere


Ecosystem functions• Ecosystems are involved with:

– Populations and their regulation – Energy use and waste processing– Nutrient cycling

• Ecological relationships develop from satisfying the essential needs of life and continuation of the species.– These relationships are manifested in physical

(abiotic) and biotic terms.


Limiting Factor

• The success of any organism or group of organisms depends on a set of conditions. E.g. – Temperature, Light, Water, Soil, Nutrients, Fire

• Any condition which approaches or exceeds the range of tolerance is said to be a limiting condition or limiting factor. E.g.– Too hot, too cold, too wet, too dry, etc


Range of Tolerance

• The ability of an organism to succeed under a variety of environmental conditions.– The range (breadth) of this tolerance is an

important ecological characteristic of a population.

– It is also an indicator of the resilience of ecosystems to external stresses.


Habitat• The physical space

where an organism lives, e.g. a pine forest or fresh water lake, a marsh.– Defined by biological

requirements of the particular organism.

– Migratory organisms require more than one geographical space.


Niche

• The functional role of an organism in a community food web. – E.g. grasses and lichens on the Tundra are

primary producers, caribou and muskox are herbivores, wolves are carnivores. Insects are pollinators. Foxes are scavengers.


Other Terms• Indicator species - an organism close to a

limiting condition. – serves as a early warning that a community or an

ecosystem is being degraded.

• Keystone species - occupies a key niche and plays a key role affecting many other organisms in an ecosystem (e.g. pollinator). – The loss of a keystone species can lead to sharp

population drops and extinction of other species that depend on it for certain services.


Ecosystem: Connections• The ecosystem is the fundamental unit of

ecology:– Ecosystems are intricately woven together by food

chains and nutrient cycles.

– Within the ecosystem, energy passes through steps or links in a food chain

• Each link in the food chain is called a trophic level (feeding level)

• Metabolic requirements in energy transformation lead to a pyramid of energy (biomass) in the ecosystem


Energy and Nutrients• Ecosystems are dependent upon solar energy flow

– Photosynthesizers convert solar energy into organic food

• Ecosystems are dependent on a finite pool of nutrients (substances that allow organisms to live, grow and reproduce):– Carbon, hydrogen, nitrogen, oxygen, phosphorus and

sulphur make up over 98 percent of body weight of life


Sustainability

• Since the supply of radiant energy from the sun is inexhaustible, ecosystems should be infinitely sustainable, if nutrients are not lost.– Under natural conditions, this is the case.– Under disturbed conditions, this is not

necessarily so.• When land is disturbed, nutrients can be lost as well

as habitat


Producers• Absorb solar energy and make organic

material from atoms in the environment.– Photosynthesis: with sunlight

6CO2+6H20 ---> C6H12O6 +6O2


Consumers

• Consume organic matter to provide themselves with energy and organic matter necessary for growth and survival.– Herbivores (consume plants)– Carnivores (consume meat)– Omnivores (plants and meat)– Detritivores (detritus)


Decomposers

• Bacteria and fungi digest organic molecules in detritus into simpler organic compounds, and absorb soluble nutrients.

• Without decomposers, many compounds would remain permanently locked up in dead organisms and hence would be unavailable for (re)use by living organisms.


Energy Flow Through Ecosystems

• Each step in the flow of food (energy) through an ecosystem is known as a trophic level, or feeding level.– Trophic = pertaining to food or nutrition.– Trophic level = position in a food chain.– Food chain (or food web) = the way that energy

passes through populations in an ecosystem.


Energy Conversion

• As energy moves from one trophic level to the next, most of the energy (90%) is given off as metabolic heat.


• A food chain is the path of food from a given final consumer back to a producer.

• For instance, a typical food chain in a field ecosystem might be:

grass ---> grasshopper --> mouse ---> snake ---> hawk

Food Chain


Trophic Levels

• The rapid loss of energy is the reason food chains have from three to four links, rarely five– This rapid loss of energy is also the reason

there are few large carnivores


Food Web

• The real world is more complicated than a simple food chain. While many organisms do specialize in their diets (anteaters?), other organisms do not. – Hawks don't limit their diets to snakes, snakes

eat things other than mice, mice eat grass as well as grasshoppers, and so on.

• A more realistic depiction of ecosystem linkages is called a food web


Food Web: Example


Biomass Pyramid

• Because energy is difficult to track in ecosystems, biomass is often used as a proxy.– Usually a large mass of plants supports a medium

mass of herbivores and a small mass of carnivores

• 1,000 kg (or kcal in an energy pyramid) of plant material converts to 100 kg of herbivore tissue, which converts to 10 kg of first level carnivores, which can support 1 kg of second level carnivores


Human Food Chains

• Humans consume about 40% of the terrestrial food supply, leaving 60% for all other land-based species on Earth.

• We note from the preceding discussion:– There is a progressive decrease in available

energy at successive trophic levels as energy is lost in metabolism.


Human Food Chains– If people eat at lower trophic levels (grains and

rice), rather than eating grain-consuming organisms such as beef cattle, they will be located on a shorter food chain.

• They will obtain more energy than meat eaters from the same amount of plant material

– The energy conversion from grain to beef is about 10:1, with another 10-fold reduction to human consumption

• For pork it is about 5:1; for industrial chicken, about 2:1


The Pyramid Scheme

• The energy/biomass pyramid explains the phenomenon of biological magnification - – the tendency for nutrients (and toxic

substances) to increase in concentration at progressively higher levels of the food chain.


Nutrient Cycles

• Despite an inexhaustible influx of energy from the sun, the continuation of life depends on the recycling of essential chemical elements, primarily– carbon, oxygen, nitrogen, phosphorous and water

• The cycling of nutrients within ecosystems is as important as the transformation of solar energy via photosynthesis


Nutrient

• Any element or compound that allows organisms to live, grow and reproduce.– However, when nutrients (e.g., phosphorus or

nitrogen) are added to water in large quantities, they promote the growth of aquatic vegetation to such densities as to degrade or alter the quality of those waters to an extent that is detrimental to their use by any plant or animal.

• An example would be eutrophication of a lake.


Nutrient Cycles

• Nutrient cycles (or biogeochemical cycles) are the ways that nutrient elements and their compounds cycle continually through the environment (via water, air, soil and food chains).

• Unfortunately, toxins can also circulate within these same cycles.


Example: The Carbon Cycle

• Carbon and Oxygen combine to form Carbon Dioxide.

• Plants use Carbon Dioxide during photosynthesis to produce sugars.

• Plants use sugars for plant growth.

• Herbivores eat plants, and incorporate molecules into their structure.


• Respiration breaks down sugars releasing CO2 and water back into the atmosphere.


Carbon is part of a Global Cycle

Human impacts?


Elements move at different rates• In the carbon cycle:

– FAST: exchange of carbon among organisms through respiration and photosynthesis (up to tens of years)

– SLOW: exchange of carbon between atmosphere and oceans (hundreds of years)

– VERY SLOW: precipitation of inorganic carbon as carbonate sediments in the ocean basins (millions of years)


Other biogeochemical cycles

• Global loops of nutrient recycling involving both biotic and abiotic components of ecosystems.– Carbon cycle– Nitrogen cycle– Phosphorus cycle– Sulphur cycle


Toxins• Toxin – a substance that causes an

immediate or long-term damaging effect when absorbed by an organism.


Bioaccumulation

• Bioaccumulation = increase in concentration of a toxin from the environment to the first organism in a food chain

• Biomagnification = increase in concentration of a toxin from one link in a food chain to another

• “Classic” example: DDT


DDT• DDT was once a widely used insecticide.

– However when washed off croplands into streams and lakes it became concentrated in fish that were ultimately eaten by birds such as bald eagles.

• The DDT caused fragile eggs such that populations of large predator birds rapidly declined.

• Since DDT was banned in the US in 1968 bird populations have made dramatic comebacks


Operation Cat Drop

• In the early 1950s, the Dayak people in Borneo suffered from malaria. – The World Health Organization had a solution:

they sprayed large amounts of DDT to kill the mosquitoes which carried the malaria.

• The mosquitoes died, the malaria declined; so far, so good.

• But there were side-effects.


Operation Cat Drop! • The roofs of people's houses began to fall down on

their heads. – DDT was also killing a parasitic wasp which had

previously controlled thatch-eating caterpillars. – Worse, the DDT-poisoned insects were eaten by

geckoes, which were eaten by cats.– The cats started to die, the rats flourished, and the people

were threatened by outbreaks of plague and typhus. • The World Health Organization was obliged to parachute

live cats into Borneo.


Year Amount Remaining0153045607590105

100 kg502512.56.253.131.560.78

DDT Persistence

• DDT has a half-life of 15 years, which means 100 kg of DDT will break down as follows:


Bioregion

• A bioregion is a land and/or water territory whose limits are defined not by political boundaries, but by the geographical limits of ecological systems.


Canada: Ecozones


Summary• Ecosystem - interacting communities

– Energy, mass, waste and nutrients flow through ecosystems.

– Linkages - food chains, food webs, nutrient cycles– Toxins follow same paths as nutrients

• Bioregion - an area defined not by political boundaries, but by the geographical limits of an ecosystem (systems).

45:211: environmental geography ecosystems: ecological principles module 4

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