Last modified on 13 September 2010, at 03:07

IB Environmental Studies


  1. Systems and Models
  2. Ecosystem
  3. Global Cycles and Physical Systems
  4. Human Population and Carrying Capacity

IB Environmental Systems Introductory NotesEdit

Strategies for Survival

Numbers ("r") large number of offspring no parental care short pregnancy breed when young pioneers niche generalists

e.g., insects, fish

Investment ("k")

late maturity specialists (niche) mainly predators high trophic level (generalization) adapted to stable environment

e.g., elephants, dolphins

Factors affecting populations

Predators - How many? Food availability - how much, where (is there need to travel?), is it difficult to obtain food? Habitat availability - are they specialists/generalists?, can they live anywhere?, Is their habitat being degraded? Reproduction - are mates easy to find? does it require much effort?

Carrying Capacity (Def: The number of organisms a particular area can support)

If organisms exceed the carrying capacity; a negative feedback loop occurs - organisms eat all the food = no food leads to dying out

Growth Rates (Def: The time a population takes to grow by a particular percentage)

It often depends on population density. populations grow fastest at low population densities (e.g., birds of prey, limited by prey availability) -Intermediate density (locusts need reasonable densities to reproduce etc.) -High Densities (seabirds less vulnerable to predators when in large group)

Fastest growth rates have quickest response to change; slow growth has slow response to changes

Generation Time (Def: The time taken for an individual to reach sexual maturity, and produce offspring)

Population grow in two ways - "S" curve- initial slow growth, as population increases limiting factors such as food supply, slow growth rate. Levels out as the population approaches the carrying capacity.

"J" curve- Large populations build up over time and then crash before building up again. Common in population of primary consumers, in communities with few species where extreme abiotic (physical) factors may control population growth. Also, natural predators are few, or completely absent.

Succession (Def: The change in vegetation in an area over time (or sometimes over distance)

Can be: Primary Succession (from bare earth) or Secondary Succession (disturbed land recovering)

Primary Succession - After a volcanic explosion/glacial scrape Dust accumulates on rock surface, seeds begin to grow.

This is the first stage in the succession process - hardy, small colonizers (typically less complex organisms) Usually occurs in dry environments with plenty of sunlight

Secondary Succession - Recovering growth from disturbed lands

Example of Forest Succession

Grass-forbs -Dominated by small grass and small shrubs

Shrubs-seedlings -Trees appear on the scene and begin to dominate. The shade intolerant species grow rapidly and dominate over shade tolerant species.

Sapling-pole

-Trees dominate and out-compete shrubs