Lecture 8: Consumer-resource Dynamics

Resources

things animals need to eat, survive, and reproduce. Eg. food, nesting sites, water, shelter. Consumption by one individual will make it unavailable to others

When is a resource pre-emptive?

temporarily lost to others. Eg. Nest boxes

When is a resource consumptive?

individuals use of resources reduces levels available to others. permanently unavailable. Eg. food

How are resources characterized/measured?

1. Amount of food available. Eg. dry mass of food per hectare

2. Suitability of that food to animals requirements. Eg. how much nutrients the animal gains from the food and often combine 2 metrics

Resource relationships

1. Interactive relationship → level of resource influences rate of increase of the population and vice versa. Eg. Bison and food

2. Reactive relationship → level of resource influences rate of increase of the population, but density of animals has no reciprocal influence on the rate of renewal of the resource. Eg. salt licks for herbivores, won’t effect rate of renewal.

Components of consumer-resource dynamics

1. Functional response of the consumer

2. Numerical response of the consumer

3. growth rate of the resource in relation to resource abundance

Benefits

1. Provide summary of dynamic ecology. Seeing how interactions change over time and how they influence each other

2. Summarizes causation instead of correlation. What causing the change in density

3. Multi-consumer systems

4. Critical Thresholds → gives indication a level of resource that cause population to increase or decrease

general theory of consumer resource dynamics

Want to understand density of resources and density of consumers

Phase Plane diagrams

Plot density of consumers against density of resources

Isoclines indicate when density does NOT change

Where the two isoclines cross is where equilibrium occurs

Stabilizing influences

self regulation by resources. Population regulation makes sure population doesn’t change too much. Carrying capacity changes.

Destabilizing influences

consumption of resource. overconsuming or disruption in environment or population.

Dynamically unstable equilibrium

outward spiral, reaches a point where it repeats. Stable limit. Eg. Hare and Lynx. big jump and drop more likely to be driven by destablizesinfluences. Easily fluctuates. The dark line is when we see population falling into sharp up and downs, straying away from equilbrium.

Stable Equilibrium

Inward spiral, stays around same number. Stabilizing influences. How they self-regulate. Eg. Lagged/delayed density response. Deer and Wolves

Paradox of Enrichment

increasing resource availability can lead to destabilization of consumers. Too much of a good thing can be a bad thing. Eg. Overpopulation of koi pond → not good, too little oxygen