Interactions Within Ecosystems0

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
• 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
– 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
– 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
• 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
Population of
same species
15.1 Population
• 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
– 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
• Ex: Remora & shark; Clown fish & anemone
– Mutualism (both species benefit)
• Ex: Cattle egret & cow; bees/birds & flowers
15.2 Symbiotic
• 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
• 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
• 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
• 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
15.3 Secondary
• Comes after a major disturbance to an
established/existing ecosystem (Ex: fire, flood,
human habitat destruction like clearing forest for
• 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
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)
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