Chapter 15 – Interactions Within Ecosystems

15.1 – Groups of Living Things Interact

15.2 – Organisms Interact Differently

15.3 – Ecosystems Are Always ChangingSource: 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

Organism

Population of same species

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:1. First - producer species is established

2. Second – decomposers & consumers arrive

3. More producers decomposers, larger consumers

4. Can happen over tens (secondary succession) or hundreds/thousands of years (primary succession)