Chapter 12: Interactions Within Ecosystems 12.1: Groups of living things interact within ecosystems 12.2: Organisms can interact in different ways 12.3: Ecosystems are always changing

Ecosystems are always changing Review: a relationship in which two organisms both try to get the same thing Competition A relationship in which both the organisms benefit Mutualism The role a species fills in a habitat niche

Populations change over time Think about a park you may have visited Years pass – More land: more trees, birds, squirrels, frogs etc. Development: concrete Communities change Organism and/or habitat changes

Population Growth and Decline Reproduction: birth rate Can increase a population or keep it stable Can merely measure the number of births or also be a measure of stability Ex: black bears reproduce once every two years If there is not enough food available, the female’s reproductive cycle is delayed and the bear population will not increase

Population Growth and Decline Predator-prey interaction impacts population size Moose vs wolves Graph: Simple models assume: 1) the prey population will grow exponentially when the predator is absent 2) the predator population will starve in the absence of the prey population (as opposed to switching to another type of prey) 3) predators can consume infinite quantities of prey 4) there is no environmental complexity (in other words, both populations are moving randomly through a homogeneous environment).

Population Growth and Decline Limiting factor: any factor or condition that limits population growth Predators may be a limiting factor for prey Prey may be a limiting factor for predators Biotic or abiotic factors serve as limiting factors Food, water, light, soil, nutrients Complex: lack of nutrients in soil Farmers add fertilizer Fertilizer runs off into a lake (river) Increases algae population Algae uses up oxygen needed by fish Fish population is limited Eutrophication

Maintaining a Balance Carrying capacity: maximum number of individuals that an ecosystem can support without considering predators Different for each population Ex: Isle Royale supports many more moose than wolves Moose is a primary consumer of plants and is lower on the energy pyramid Limiting biotic factors: interactions between populations Competition, predation, parasitism Limiting abiotic factors: Temperature, availability of water or minerals, wind

Ecosystems change over time Succession: the gradual change in an ecosystem One biological community is replaced by another Field to a forest, farmland to plants, shrubs, and trees

Primary Succession The establishment of a new biological community Plants move into an area that was previously barren Pioneer species: first living things to move into a barren environment Glacial retreats: mosses and lichen move in As they grow, they weaken the rock surface New soil is formed and a variety of small plants and shrubs can take root And so on…

Secondary Succession Takes place after a major disturbance to a biological community in a stable ecosystem Ex: natural event: fire, flood, etc; or human activity: forest cleared, farmland abandoned Soil remains, and seeds and plant roots survive

Patterns of Change Ecosystems go through successions Can forest, wetland, coastal, ocean community Can happen over tens or hundreds of years Pattern is still the same: Community of producers is established Followed by decomposers and consumers, then more producers, etc. Pioneer species can either: Help other species to grow Alders have N-fixing bacteria on their roots, improving soil quality Also good for shade and nutrients when they die Or prevent species from getting established Plants may release chemicals to keep other plants from takeing roots New species may outcompete others by using up resources or better resisting disease