Principles of Ecology

Principles of Ecology

Definitions

Ecology: the study of how living organisms interact with each other and with their abiotic environment.

Abiotic Factors: non-living components of the environment.

Habitat: the organism place of residence to which it is adapted.

Population: a group of individuals of the same species living in the same area that interact and interbreed with each other.

Community: interacting populations of different species living in the same area.

Ecosystem: a community of organisms and the habitat’s non-living components.

Biosphere: the global ecosystem - the Earth’s ‘layer of life’.

Environmental Factors Affecting Living Organisms

Biotic Factors: the effect of other living organism of the same or other species.

Abiotic Factors: the effect of non-living items of the organism’s habitat.

Climatic Factors: the effect of the average weather conditions over time, e.g., temperature, rainfall, day length, humidity, wind, atmospheric pressure.

Edaphic Factors: the effect of soil conditions e.g. pH, aeration, porosity, water content, mineral nutrients, humus, soil type.

Aquatic Factors: e.g. wave action, tides, submergence time, exposure time, salinity, oxygen concentration, currents, sedimentation and light quality.

Nutritional Types of Organisms

Producer (Autotroph): makes its own food from inorganic materials.

Photosynthesis: light is the energy source.

Chemosynthesis: energy released by chemical reactions is the energy source.

 Consumer (Heterotroph): cannot make food - uses ‘ready-made’ food.

Herbivore: plant eating animal e.g. rabbit, honey bee, green fly.

Carnivore: flesh eating animal e.g. fox, hawk, ladybird.

Omnivore: plant and flesh eating animal e.g. hedge hog, field mouse.

Decomposer: detritus feeder e.g. earthworm, most bacteria and fungi.

Saprophyte: bacterium or fungus that feeds on detritus.

Feeding Relationships

Food Chain: a list of species, each being food for the next species in the list, i.e.

Grass  >  Rabbit  >  Fox

Bramble >  Aphid  >  Ladybird  >  Sparrow  >  Hawk

Trophic Level: the position of a species in a food chain.

Bramble: first trophic level or primary producer.

Aphid:  second trophic level or primary consumer.

Ladybird: third trophic level or secondary consumer.

Sparrow: fourth trophic level or tertiary consumer.

Hawk:  fifth trophic lever or quaternary consumer.

Short Food Chains

Inefficiency of energy transfer to the next trophic level.

The energy needs of each organism is about 90% of its food intake.

Almost 90% of an organism’s food is used in respiration.

Food Web

A food web is a flow chart showing the feeding connections in a community.

Textbook Diagram: food web diagram.

A food web is made by linking food chains.

The links are food sources used by two or more species.

All species in a community are connected through the food web.

A change in any one species causes changes in all populations.

Pyramid of Numbers

A Pyramid of Numbers is a bar chart showing the number of individuals at each trophic level of a food chain.

Textbook Diagram: normal and inverted pyramids of numbers.

         

The number at each trophic level is influence by:

Energy needs of an individual - the lower the need the great the population.

Mass of an individual - the greater the mass the greater its energy needs.

Energy transfer - only about 10% is transferred to the next level.

Other food sources - the species may be a member of other food chains. 

Energy Flow

Textbook Diagram: flow char for energy flow.

About 1% of sunlight energy used for photosynthesis by primary producers.

Each trophic level 90% of the food is used for respiration and lost as heat.

Only  about 10% of the food energy is transferred to the next trophic level.

Detritus (dead organic matter) is a very important energy source.

Ecological Cycles

Nutrient Cycling

Textbook Diagram: mineral cycling flow chart.

Carbon dioxide is the source of carbon and oxygen for organic molecules.

Water is the source of hydrogen for biomolecules.

Plants get the other elements as soluble salts from the abiotic environment.

Plants are the direct or indirect source of nutrients for consumers.

Consumers ‘steal’ the materials they need, as food, from other organisms.

Decomposers return the inorganic nutrients to the abiotic environment.

Carbon Cycle

Textbook Diagram: carbon cycle flow chart.

Carbon is the most important element in biomolecules as it forms their skeletal framework.

Nitrogen Cycle

Textbook Diagram: nitrogen cycle flow chart.

Bacteria in the Nitrogen Cycle - how they benefit from their roles in the nitrogen cycle:

Nitrogen Fixing Bacteria: usuable form of nitrogen for biomolecule formation. 

Saprophytic Bacteria: receive a  supply of materials for energy, growth and reproduction. 

Nitrifying Bacteria: produce ATP by the nitrification process.

Denitrifying Bacteria: nitrites and nitrates are their oxygen source for ATP formation.

Biotic Factors

Competition

Competition is the rivalry between individuals of the same or different species for the same resources.

Plant Example: grass and daisies compete for light, space, water.

Animal Example: fox and hedgehog compete for food e.g. earthworms.

Competitive Adaptations

Yellow petals of buttercup flower: to win the battle for insect pollinators.

Antibiotics secreted by soil bacterial to inhibit their competitors for nutrients.

Ecological Benefit of Competition

Controls and limits the size of the competitive species.

Maintains a species at a sustainable level.

Competition is a major factor in the evolution. 

Important factor in maintaining the ‘balance of nature’ in the community.

Predation

Predation is the hunting and killing of one animal by another for food.

Examples: fox killing rabbits; ladybird killing aphids.

Ecological Benefit of Predation

Maintains the prey species at a sustainable level.

Predation is a major factor in the evolution of the prey species.

Predator Adaptations, e.g., fox.

Reddish fur: camouflage to avoid detection by rabbits. 

Long canine teeth: to kill the prey and tear flesh from it when feeding.

Great speed: to outrun the prey to capture it.

Prey Adaptations, e.g., rabbit.

Rests underground: predator avoidance.

Long ears: good hearing to detect the predator.

White tail: conspicuous warning signal to other rabbits.

Textbook Diagram:  Predator-Prey Graph - Know how to interpret this graph.

Symbiosis

Symbiosis is the relationship between individuals of two or mores species living together.

Commensalism: symbiosis where one species gains benefit and the other species does not gain but is not at any serious disadvantage. Example: lichens and trees - the lichens gain a place to grow.

Parasitism: symbiosis where one species feeds off and harms the other. Example: lice on hawks.

Mutualism: symbiosis where all species gain. Example: lichens - the fungus gains food from the algae and the algae gain shelter, water plus mineral nutrients from the fungus.

Niche

A species niche is everything about how it lives and fits into the community.

Each species in a community has a unique niche.

Human Population

Food supply and disease are the major factors affecting human population.

Great prosperity is a major factor influencing the population of developed countries.

Textbook Diagram: Human Population Graph

The greater the food supply the greater the potential for population growth.

Famine reduces the population - death and/or migration.

Famine is often linked to war - war zones have reduced agricultural activity.

Prosperity leads to population reduction due to a decline in the birth rate.

Convenient, effective and easily available contraception reduces the birth rate.

Disease, especially among infants, often results in a high death rate.

Modern medical practice has massively reduced the death rate from disease.

Modern medicine and absence of contraception has led to hugh population increase in many developing nations.