Introduction to Ecosystem Ecology PP 403-404

Ecosystem Ecology Ecosystems are the interactions of different populations (communities) and the abiotic factors of the environment Species  Population  Community  Ecosystem  Biosphere

LOGISTIC MODEL review

Models the growth of a population over time Starts off exponential (b> d) but levels off as the population reaches carrying capacity (K) Carrying capacity (K) is the maximum number of individuals an environment can sustain K is when b rates equals d rates or zero population growth Limited by factors that increase in pressure as the population density increases (density-dependent factors) EX. predation, pollution, disease, resources, mates

PREY: SEA URCHINS Prey PREDATOR: SEA STARS Predator

Predation Example One species eats (predator) another species (prey) The relationship is cyclic in nature – ↑ in prey leads to ↑ in predators, ↓ in prey leads to ↓ in predators, and so on The size of the predator population is always changing or fluctuating around a set point called carrying capacity

FEEDBACK MECHANISMS IN ECOLOGY Process that uses the conditions of one component to regulate the state of the another

Negative feedback results when the a change occurs in one element that affects the other in the opposite direction The net result produces a stable system where different forces are counterbalancing each other out creating some equilibrium. Negative Feedback

Positive Feedback Positive feedback is responsible for sudden or rapid changes within ecosystems When part of the system increases, another part of the system also changes in a way that makes the first part increase even more. Positive feedback is self-reinforcing and a source of instability that can drive the ecosystem outside of its normal operating parameters.

QUESTION: Is the population model of the predator-prey relationship an example of negative feedback or positive feedback? Cite one reason for your choice.

Stability and Change Ecosystems are constantly changing and fluctuating around a set point Ecosystems are characterized by both stability and change Change can be a healthy component of the ecosystem but also unhealthy when influenced by human impact

TASK: Provide 2 pieces of evidence for stability or change from the Pika video. https://www.youtube.com/watch?v=pnc2y3tRmcQ