Population Dynamics

Lots of factors affect populationsThe organisms themselvesThe habitatHow they reproducePredator – prey interactions (and lots more!!)

Populations change over time

Check out the predator/prey relationship on the graph

This is any factor or condition that limits the growth of a population in an ecosystem.

Eg: A large population of predators will limit the population of prey but a small population of prey will limit the population of predators.

Too much or too little of biotic or abiotic factors makes an ecosystem unstable change.Food, water, light, nutrients, algae using up

oxygen etc.

Limiting Factor

Example of predator / prey relatioship

Living things have certain minimum requirements for food, water and living space.

When a population can no longer grow it has reached its carrying capacity. This is the maximum number of individuals that an ecosystem can support.

It is different for each population.

Both biotic and abiotic factors can be limiting: interactions between populations (competition, predation, parasitism); temperature; availability of water; minerals; exposure to wind etc.

Carrying Capacity

Example of carrying capacity

SuccessionThe gradual change in an ecosystem in which

one biological community is replaced by another.

Ecosystems change over time

When plants move into an area and bring it back to life. A new biological community is formed.

After a lava flow After a glaciar retreats.

Primary Succession

The first living things to move into a barren environment. Often moss, lichen etc. They grow, start to break down rock etc and prepare the environment for forests.

Pioneer species

Takes place after a major disturbance.Soil is still there. It is more surface damage.Could be a fire, flood, human activity.

Secondary Succession

A species that has a disproportionately large effect on its environment relative to its abundance.

They play a critical role in the structure of an ecological community.

Help to determine the types and numbers of various other species in the community.

An ecosystem may experience a dramatic shift if a keystone species is removed, even though that species was a small part of the ecosystem by measures of biomass or productivity.

Keystone species

Some sea stars may prey on sea urchins, mussels and other shellfish that have no other natural predators.

If the sea star is removed from the ecosystem, the mussel population explodes uncontrollably, driving out most other species, while the urchin population annihilates coral reefs.

Example

Sea otters protect kelp forests from damage by sea urchins.

Kelp "roots", called holdfasts, are anchors, and not the vast nutrient gathering networks of land plants.

Sea urchins only need to eat the roots of the kelp, a tiny fraction of the plant's biomass, to remove it from the ecosystem.

Another example

1. Describe three factors that could limit the size of a population in a habitat.

2. List two natural disturbances and two human-made disturbances that can lead to succession.

3. What role do pioneer species play in succession?

4. Imagine you are the wildlife manager for a forest reserve that supports both moose and wolves. What types of information should you collect to determine the carrying capacity for each species?

5. What are keystone species?

What did you understand?

Objective: to enhance your understanding of population dynamics you are going to open a new habitat and then simulate competition between foxes and mice that are going to use the habitat.

Now YOU are going to work with predator and prey ‘species’

Participants

Control Beads (Other animals found in the habitat)

5 / group1 person records data and adds beads4 people are predators

Group roles

1) Each generation will begin with at least 10 mice and 1 fox.

2) The mice will double their surviving number each generation.

3) The habitat can support no more than 100 mice (its carrying capacity)

4) Each predator in each generation MUST capture at least 5 mice to survive and produce offspring.

5) Yellow control beads should always be returned after EACH predator has had a turn.

6) Predators MAY NOT LOOK while picking out the beads.

Basic rules

The Data Sheet (per person)

The Graph

Remember:X = preyO = predatorJoin the lines