Chapter 15 – Interactions Within Ecosystems 15.1 – Groups of Living Things Interact 15.2 – Organisms Interact Differently 15.3 – Ecosystems Are Always Changing Source: McDougal Littell – 6th Grade Science

15.1 Groups of Living Things Interact … Organisms occupy specific living areas The smallest grouping is a species (animals that can reproduce and whose offspring can reproduce) Population = a group of organisms (plant or animal) of the same species that occupy a particular area (ex: cacti, scorpions, rattlesnakes) The boundary of an area defines a population. (Ex: cacti do not live in the same area as crabs, nor crabs with iguanas, but all 3 populations live on the Galapagos Islands)

15.1 Habitats & Niches Habitat = Physical location where plants and animals live Physical characteristics of a habitat = Rainfall, temperature, soil quality Determine which plants/animals live there Determine which role/niche a plant or animal occupies No two species fill the same niche Niche is more than plant/animals role in food web. (Ex: Plants provide nesting as well as produce food)

15.1 Communities A biological community is a group of populations that live in a particular area and interact with each other. The environment can be organized into 5 levels: Biome, Ecosystem, Community, Population (of Species) & Organism

15.1 Ecosystem’s 5 levels Biome = largest; describes in general terms the climate and types of plants/animals found in similar places. May contain several ecosystems within it. Ecosystem = The living & non-living factors that interact to form a stable system. (smaller than a biome & includes only organisms and their local environment). Community = living components of the ecosystem that interact with each other Population = group of organisms of same species living in an area. Organism = single individual (plant/animal)

15.1 Environment’s 5 levels Biome Ecosystems Communities Population of same species Organism

15.1 Population Patterns Populations may be crowded together (schools/herds), spread apart, live in community groups, rise & fall with seasons, etc. The distribution of animals/plants in a habitat is determined by how they meet their needs for food, water, shelter, nest space Patterns in time = seasonal migrations of species (immigration into population/area or emigration from a population/area), spring births, winter deaths, etc.

15.2 Different Ways Organism Interact Survival of one species might depend on another species (producers & consumers) Symbiosis = relationship between individuals of two different species who live in close relationships Competition – struggles between organisms (same species) or populations (different species) for limited resources Predator-Prey (predator benefits; prey harmed) Ex: Hawk & mouse; Strangler fig & tree Parasite-Host (parasite benefits; host species harmed)

15.2 Cooperation Interactions Not all animals of a species compete to survive. Some species cooperate to survive Ex: bees, ants, wolves, whales Commensalism (one benefits; the other is not affected) Ex: Remora & shark; Clown fish & anemone Mutualism (both species benefit) Ex: Cattle egret & cow; bees/birds & flowers

15.2 Symbiotic Relationships An ecosystem is more than just a collection of biotic & abiotic factors… There are 3 types of symbiotic relationships which may overlap within any ecosystem and one species may be involved in more than one type of symbiotic relationship Mutualism (both species helped) Commensalism (one species helped; one unaffected) Parasitism (one species helped; host species harmed)

15.3 Ecosystems Change Populations change over time due to a variety of reasons: competition, predation, drought, etc. Any factor(s) that limits growth of a species = a limiting factor Too much/too little of any abiotic/biotic factor Ex: poor soil; too many predators Carrying capacity (cc`) = maximum number of individuals an ecosystem can support CC is different for each population in an ecosystem Ex: A river can support more turtles than alligators; more moose (herbivore) than wolves (apex predator)

15.3 Succession Changes Succession = the gradual change in an ecosystem in which one biological community is replaced by another: Ex: Grassland becoming forest Primary Succession = No prior species existed before new biological community becomes established (Ex: barren rock on lava flow. )Very slow process. Secondary Succession = Takes place after major disturbance in an established ecosystem (Ex: forest fire burns forest, but soil remains). Happens more rapidly due to remains (soil, seeds, etc) of prior ecosystem

15.3 Primary Succession No prior life exits (Ex: new lava flow, or glacier) Takes a long time for pioneer species to move in and soil to be established (they stabilize soil, shade soil, add nutrients when they die/decay) Pioneer species = the first living things to more into a barren (no life exists)ecosystem. Ex: Pioneer Species = Mosses, lichens cling to rocks and begin soil formation on a lava flow. After soil is formed, seeds for small plants & shrubs can take root, small animals appear Finally large shrubs & trees appear, more animals appear

15.3 Secondary Succession Comes after a major disturbance to an established/existing ecosystem (Ex: fire, flood, human habitat destruction like clearing forest for farmland). Happens much faster as soil is already formed & residue of prior life exists (seeds, underground roots, etc) Ex: Fire destroys forest; soil remains Some trees regenerate from surviving roots/seeds as do grasses, shrubs. Small animals return Large hardwood/deciduous trees return over time; more animals return

15.3 Patterns of Change All types of ecosystems have succession changes: grasslands, wetlands, river systems, forests, oceans, etc. Pattern always remains the same: First - producer species is established Second – decomposers & consumers arrive More producers decomposers, larger consumers Can happen over tens (secondary succession) or hundreds/thousands of years (primary succession) e