1. 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

2. 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)

3. 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)

4. 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

5. 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)

6. 15.1 Environment’s 5 levels Biome Ecosystems Communities
Population of same species
Organism

7. 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.

8. 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)

9. 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

10. 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)

11. 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)

12. 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

13. 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

14. 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. 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