Ecosystems & Populations

Definitions

Ecosystem → Combination of the community of organisms living in a habitat and their interactions with each other and the physical environment.

Abiotic Factors → Not due to living things e.g rainfall & temperature.

Biotic Factors → Living things in the habitat, part of the environment due to living things e.g Disease.

Community → Interacting populations in the same area at the same time E.g Trees and undergrowth plants.

Habitat → Where an organism lives e.g Woodland, Tree.

Competition → Relationships between organisms for resources in the same area at the same time.

Environment → Combination of physical, chemical and biological factors that act upon an organism.

Population → Group of organisms of the same species in a defined area.

Density Dependent Factor → Factors that increase as population increases E.g Availability of Food.

Density Independent Factor → Factors that decrease the number population E.g Flood, WIldfire.

Ecological Niche → The role, activities and location of an organism within a habitat. No two organisms occupy the same niche.

Ecosystems

Aspects of ecosystems are subject to change,

• Energy flows

• Population sizes

• Species composition

• Biological Cycles

Population Growth

• A population will grow when its biotic potential is greater than the environmental resistance until it reaches its carrying capacity.

• Rate of growth= Birth Rate- Death Rate +/- Net Migration

• Biotic Potential - Organism feed & breed & produce offspring.

Density Dependent Factors

• Effects are stronger as population density increases.

• Usually caused by living things.

• May increase mortality or decrease fertility.

• E.g; Disease, Parasitism.

Density Independent Factors

• Effects are not related to population size.

• Extreme temperatures, drought, rain& floods, snow, fire natural disasters.

Population growth curve.

• Lag Phase - Populatiom becoming established.

• Exponential Phase- Births>Deaths.

• Stationary Phase- population@ carrying capacity.

• J-Shaped- Short-lived organisms.

• S-Shaped- Longer living animals with few predators.

Calculating Population Increase

• We use log numbers.

Food Chains

• Direction in which high energy flows.

• Trophic Levels.

• Producer→Primary consumer→Secondary Consumer

• Food Webs give a larger image of energy flow.

• Energy is lost at each link in the chain.

• Numbers decline as they go up.

• Food pyramids use numbers, energy or biomass to put into pyramids of numbers.

Why does Biomass and energy decrease?

• Energy is lost to the environment.

• Photosynthesis uses energy that is lost to the environment.

• Plants do not absorb all light energy.

• Carnivores only eat a portion of their food and can only partially digest food.

• Heat is lost during respiration.

• In herbivores, only 10% of the energy ends up as herbivore biomass. They are inefficient at converting cellulose.

• Carnivores are more efficient because they can digest a high protein diet more efficiently.

Photosynthetic Efficiency.

• Photosynthesis ia the basis of most food chains as plants are autotrophic.

• Photosynthesis is also known as primary production.

• This also incluses chemosynthetic producers..

• Phorosynthetic efficiency is a measure of how well a plant is able to capture light energy.

• Plant losses from solar energy → reflection of green light, photosynthesis & respiration.

Gross Primary Productivity- Rate of production of chemical energy in organic chemicals by photosynthesis. Kj/cm^2 per year.

Net Primary Productivity- GPP minus the chemical energy generated in respiration and used in metabolism per year.

GPP = NPP + Respiration

NPP = GPP-Respiration.

GPP is the potential food energy available to heterotrophs in ecosystems.

Measuring Population Size and Density

Reliable population estimates are essential for wildlife conservation and population management.

Population Density; Total Number in all quadrats sampled

No of quadrats sampled x Area of a quadrat.

For moving animals we use Mark-Capture-Release.

1. Select co-ordinates for trap sizes on a sampling grid of the habitat using a suitable number of traps.

2. Place the traps, come back and collect and count the animals caught.

3. Mark in a non harmful way

4. Afyer a suitable time period go bacl and select a second sample counting the arked and non marked individuals.

Lincoln Index = n1 x n2

Nm

Changes in Ecosystems- Succession

Succession - THe change in structure and species composition of a community over time.

Things will change and continue to change until is becomes a climax community.

Primary succession- No previous vegetation and then development begins as plants move in.

Secondary succession- Colonisation of an area where organisms are already present.

Deflected Succession - A deflected succession is one where succession does not succeed to the expected climax community for its location.

Often caused by human activity.

Results ina community called a plagioclimax.