Module 4 - Ecosystem Dynamics

Population Dynamics

What effect can one species have on the other species in a community?

investigate and determine relationships between biotic and abiotic factors in an ecosystem, including:

•  the impact of abiotic factors

Definition: Physical/chemical parts of the environment that affect organisms.

Examples: temperature, water, light intensity, soil nutrients, salinity, pH, oxygen.

Impact:

• Control distribution and abundance of species.
  
  

• E.g. drought reduces plant growth → fewer herbivores → fewer predators.
  
  

• Abiotic changes (e.g. climate change, pollution) can shift niches or eliminate species.

the impact of biotic factors, including predation, competition and symbiotic relationships

• Predation

Predation:

• Predators limit prey numbers; prey abundance affects predator survival.
  
  

Results in population cycles (boom/bust patterns).

the impact of biotic factors, including predation, competition and symbiotic relationships

• Competition

Competition:

• Intraspecific: competition within the same species (e.g. mates, food, nesting sites). Controls density.
  
  

• Interspecific: competition between different species for the same resource (e.g. lions vs hyenas).
  
  

• Competitive Exclusion Principle: no two species can occupy the same niche indefinitely → one outcompetes the other.
  
  

• Resource Partitioning: species can reduce direct competition by using resources differently (e.g. birds feeding at different tree heights).
  

the impact of biotic factors, including predation, competition and symbiotic relationships

• Symbiotic Relationships

Symbiotic Relationships:

• Mutualism (+/+): both benefit (e.g. bees + flowers).
  
  

• Commensalism (+/0): one benefits, other unaffected (e.g. remora + shark).
  
  

• Parasitism (+/–): parasite benefits, host harmed (e.g. tapeworm + human).

the ecological niches occupied by species

Definition: The role/position of a species in its ecosystem (how it survives, feeds, reproduces, interacts)

Fundamental Niche

Fundamental Niche: full range of conditions/resources a species could theoretically occupy without competition.

Realised Niche

Realised Niche: the actual conditions/resources a species occupies in reality, restricted by competition, predation, and other interactions.

the ecological niches occupied by species

• Examples

Examples:

Barnacles: one species’ fundamental niche is larger, but competition with another barnacle species restricts it to a smaller realised niche.

the ecological niches occupied by species

• Key Ideas

Key Ideas:

• Competitive exclusion limits overlap between species.
  
  

• Resource partitioning allows coexistence.
  
  

• Generalist species (e.g. humans, rats) = broad niche → adaptable.
  
  

• Specialist species (e.g. koalas) = narrow niche → vulnerable to change.

predicting consequences for populations in ecosystems due to

• predation

Predation

• Predator numbers affect prey population size (increase in predators → decrease in prey).
  
  

• Prey availability influences predator survival.
  
  

Example: Food webs and food chains show predator-prey relationships.

predicting consequences for populations in ecosystems due to

• Competition

Competition

• Intraspecific (within the same species): competition for mates, territory, resources.
  
  

• Interspecific (between different species): can lead to competitive exclusion (one species outcompeted) or resource partitioning (species share resources differently).
  
  

• Affects population size and distribution within the community.

predicting consequences for populations in ecosystems due to

• Symbiosis

Symbiosis

• Mutualism: both species benefit (e.g., pollinators & plants).
  
  

• Commensalism: one benefits, other unaffected (e.g., barnacles on whales).
  
  

Parasitism: parasite benefits, host harmed → may reduce host population.

predicting consequences for populations in ecosystems due to

• Disease

Disease

• Pathogens spread within populations (density-dependent).
  
  

• Can reduce numbers, sometimes regulate population size.
  
  

• Impacts food webs (e.g., disease in prey → predators also decline).