Principles of Ecology (chpt 38)

Ecology

Study of interrelationships of plants and animals w each other and w their environment

Ecosystem

Organisms and their interactions with their environment

Biosphere

All parts of earth where life exists

Regions: lithosphere (land), hydrosphere (water), atmosphere (air), cryosphere (ice)

Habitat

Place where a species lives

Aboitic factors

Non-living features of the environment: climate factors (macro and micro), edaphic (soil)

Climatic Factors

Influence of prevailing weather conditions. Macroclimate; global or regional, microclimate; small habitat eg. log or cave

Macroclimate

• Light intensity: eg. daisies only grown in strong light exposure, like lawn, but bluebells can photosynthesise w little light, like woodland

• Temperature: Important in controlling rate of chemical reactions. Temperatures in air fluctuate more than in water as able to retain heat, therefore organisms in water less tolerant to heat changes. Effects solubility of gases in water also, increase in water temp, decrease in solubility of gases

• Exposure

• Day length

• Rainfall

• Wind speed

• Salinity

• Wave action

• Humidity

Edaphic factors

Abiotic factors relating to soil

• pH: acidity/alkalinity of soil affects availability of nutrients to plants

• Mineral content: determined by underlying bedrock

• Water content

• Humus

• Porosity

• Air content

• Soil type

Biotic factors

Influences of living organisms on each other

• Feeding

• Disease

• Pollination

• Nitrogen-fixing bacteria

• Decomposers

Energy flow

• Law of conservation of energy states energy cannot be created or destroyed but only changed from one form to another

• Main source of energy is the sun (1% trapped in plants)

• As energy passes from one organism to the next, about 90% is used/lost as heat, excretion, and egestion or used in growth and respiration. Only 10% assimilated

Producers (Autotrophs)

• Chemosynthetic: make own food using chemical energy, eg. nitrifying bacteria in soil and bacteria in deep-sea volcanic vents

• Photosynthetic: make food from light

Consumers (Heterotrophs)

• Herbivores: Eat producers, mainly plants (Primary consumers). Ridged teeth to crush grass, long intestines to digest it, with aid of bacteria to break down cellulose. Produce methane

• Carnivores: Eat herbivores and other carnivores (ie mainly meat)

• Omnivores: Eat both plants and animals and have adaptations intermediate of the two

• Detritus feeders: Eat remains of dead plants and animals, eg. dugesia in ponds, woodlice/worms in forest

• Decomposers: Break down dead plants and animals into basic components by extracellular digestion, eg. fungi and bacteria

Food Chain

Feeding relationship between plants and animals (and microorganisms)

Trophic levels

Position of an organism in a food chain

Trophic Levels:

1. Primary producers (usually green plants)

2. Herbivores (primary consumers) eat first trophic level species

3. Carnivores (secondary consumers eat herbivores in second trophic level

4. Carnivores (tertiary consumers) eat carnivores in third trophic level

Food web

Two or more interconnected food chains

Pyramid of numbers

Chart showing number of organisms at each trophic level

Limitations:

• If organism is very large, eg. oak tree, one tree may house thousands of greenfly → inverted pyramid

• Parasites create parasitic pyramid

Niche

Functional role of an organism in its habitat

Nutrient recycling

Movement of essential elements from abiotic environment into living organisms and then returning to the abiotic environment to be used again

Carbon cycle

• Concentration of CO₂ is 0.03%. Sea acts as buffer for CO₂ concentration by dissolving it at night when concentration rises and releasing it during day when it drops

• Plants → (animals) → dead matter → respiration in microorganisms/carbon in fossil fuels → CO₂ in atmosphere

Nitrogen cycle

• Atmosphere: 80% nitrogen in form of N₂ gas

• To be available to plants and animals needs to be converted into nitrates NO₃⁻ which can be absorbed. Occurs by action of nitrogen-fixing bacteria and lightning. Also artificially by humans by Haber process

• Nitrates enter soil in rain, absorbed through roots. Used to produce proteins → assimilated into animals when plants are eaten

• some nitrogen lost in excretion mainly in form of urea. When plants and animals die, decomposed by bacteria and fungi, nitrogen-containing compounds found in bodies converted to ammonia

• Ammonia converted to nitrites NO₂⁻ by bacterial action → nitrification. Nitrites are toxic to plants so not absorbed. Nitrites converted to nitrates by other bacteria (also nitrification)

• In soil, chemosynthetic bacteria break down nitrates releasing nitrogen gas back into atmosphere and completing cycle → denitrifying bacteria (most live in stagnant waterlogged soil

Biodiversity

Large variety of organisms in an ecosystem

Pollution

Any harmful addition to the environment

Conservation

Wise management of existing resources to maintain existing populations

Conservation Practises:

• Agriculture: Slurry is very rich in nutrients and used as fertiliser, should only spread in dry weather and no closer than 10m from watercourse → prevents run-off into water courses, preventing eutrophication

• Fisheries: Setting minimum mesh size allows young immature fish to escape netting and reach breeding age. Prevents depletion of fish stocks. Can also be augmented by applying quotas of endangered commercial species

• Forestry: Removal of biological material from woodland on a regular bases can result in ground becoming depleted in nutrients. To prevent this, fallen or cut leaves and branches should be left to rot naturally on forest floor. Maintains constant supply of nutrients for trees

Eutrophication

Excess plant growth caused by excess nutrients. When nutrients run out, algae that has grown dies and rots due to bacterial action. These bacteria use up all the oxygen in water, killing most of animal life it contains. Slurry also contain pathogens, eg. cyrptosporidium, which can infect people and animals

Waste management

Main ways to dispose of waste: landfill and incineration

Problems w waste disposal:

• Vermin: Waste attracts vermin, eg. rats and gulls. Rats carry disease (eg. Weil’s disease) and destroy food and property. Gull’s droppings also carry disease and are problem near airports, where bird strikes can cause damage to planes

• Odours; rubbish dumps have pervasive odours which are unpleasant for those that live nearby

• Contamination: Waste can contaminate groundwater when unsuitable items are left at dumps. Batteries contain heavy metals, eg. lead and cadmium, can leach into groundwater

• Toxic products: Burning rubbish reduces bulk in landfill sites, heat produced through burning can be used to heat local houseing, or treat other waste to make it biologically safe, however some products of incineration, eg. dioxins, can be toxic or carcinogenic

Importance of waste minimisation

• Reduce: Amount of waste, especially packaging. Can be reduced by choosing to buy items w less packaging

• Reuse: Packaging, eg. plastic bags, or by bringing reusable shopping bags to supermarket. Results in saving financially and helps conserve valuable resources

• Recycling: Collecting materials and using them again for same purpose or modifying them for different purpose, eg. recycled plastics are washed, shredded and reused to make other products

Role of Microorganisms in Waste Management and Pollution Control

• Sewage treatment: Sewage made safe by biological oxidation using microorganisms to break down organic waste and destroy pathogens. Remnants are then composted or heat-treated before spread on land as fertiliser or disposed of in watercourses/sea (tightly controlled by legislation)

• Bioremediation: Uses microorganisms to remove pollution and allow area to revert to its unpolluted state. eg. oil spills, deactivating pesticides, converting mercury or arsenic to non-toxic forms

Competition

Struggle between organisms for resources that are in short supply

• Intraspecific competition: competition between members of same species

• Interspecific competition: competition between different species (harder to demonstrate as each species has own particular niche and only partially overlap → tends to be short-lived

2 types of intraspecific competition

• Contest competition: winner takes all and as a result has excellent chance of survival and producing offspring. Loser is marginalised to poorer areas of habitat. As a result, loser may not survive or will have difficult time rearing offspring successfully. Usually for the right mate, or for territory

• Scramble competition: each individual gets some of the resource without direct physical confrontation w other members of species. Works as long as resources are not very scarce. If resources become scarce, can result in population crash as no individual will get enough to support reproduction and survival. eg. Lackey moth caterpillar. Concregate in what look like spiderwebs on blackthorn/hawthorn bushes.

Role of competition

• Controls population size by ensuring least members get enough resources

• Only fittest and best adapted to environment will survive

• Results in natural selection, and therefore evolution

Adaptation

Any change in the behaviour or structure of an organism that makes it better suited to its environment

Types of Adaptation

1. Behavioural

   • Plants: grow towards light, fast growing, deep roots to find water and minerals, etc. eg. bindweed twines around plants to grow upwards quickly without need for supportive tissue

   • Animals: Birds singing to deter other birds, rooks fly in flocks to make it more difficult for predators to catch them, frogs bury in mud in bottom of ponds in harsh weather

2. Structural

   • Plants: Hawthorn and gorse bushes have thorns to deter browsers, nettles have stings to achieve same, pea pods burst open to scatter seeds

   • Animals: Snails grow shells to protect against predators and adverse weather, peacock butterfly has eyes on wings to startle predators

3. Colouration

   • Plants: Bright colours attract pollinators, grow leaves that look like they have been damaged by insects/disease

   • Animals: Wasps have yellow and black stripes to warn they are dangerous (aposematic colouration), other animals blend into surroundings, eg. woodcock (cryptic colouration)

Prey

Animal that is caught and killed for food

Predator

Organism that catches and kills animal for food

Predation

Act of catching and killing animal for food

Symbiosis

Close relationship between two species, where at least one of the species benefits

Types of Symbiosis

• Parasitism: One species benefits, other is harmed. Species that benefits is the parasite, species that suffers is the host

• Mutualism: Both species benefit, eg. bacteria that produce vitamins B and K

• Commensalism: One species benefits while other is neither harmed nor benefits, eg. bird in tree, barnacles

Population Dynamics

Study of changes in populations and factors that cause these changes

Predator-Prey Relationship

Plenty of food, herbivores thrive and rapidly multiply. Predators are less abundant, however w plenty of available food, predator population grows rapidly also. Will eat all prey except a few, both populations crash. Cycle repeats

Factors Affecting Human Population

• War: In particular regions have marked impact, but globally, effects are less

• Diseases: both infectious (no physical contact) and contagious (physical contact required) play significant roles. Epidemic is large number of people in given population in short period of time. Pandemic is a disease outbreak across a continent or world. Study of spread of diseases is epidemiology

• Famine: Sever and prolonged lack of food in widespread area, often followed by regional malnutrition, starvation and epidemics, resulting in increased mortality

• Contraception and Improved Education: Helps to control population growth, particularly in developed nations