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.

Select co-ordinates for trap sizes on a sampling grid of the habitat using a suitable number of traps.
Place the traps, come back and collect and count the animals caught.
Mark in a non harmful way
Afyer a suitable time period go bacl and select a second sample counting the arked and non marked individuals.

Lincoln Index = n1 x n2

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.