Uploaded by Dominique Fae


Community Interactions
Levels of Organization
• Ecologists study organisms and their
environments at different levels of
– Biosphere: consists of all organisms on Earth
– Biome: group of ecosystems that have the same
climate and dominant communities.
– Ecosystem: consists of living things and their
– Community: consists of populations of
different species that live in the same area
and interact together.
– Population: organisms of the same species
that live in the same area, interact with one
another, and produce fertile offspring.
– Organisms: are individual living things.
This is the lowest level of organization that
ecologists study. Biologists study organisms,
organ systems, organs, tissues, cells,
organelles, and molecules. Chemists study
atoms and subatomic particles.
Organisms and the Environment
• Organisms: life form consisting of one or
more cells; has characteristics of life.
• Environment includes both living (biotic)
and nonliving things (abiotic).
Biotic and Abiotic Factors
• Biotic living organisms
• Abiotic nonliving or physical factors
• Together determine productivity of the
ecosystem in which organisms’ live
Community Interactions
• Powerfully affect an ecosystem
• Include:
– Competition
– Predation
– Symbiosis
• When organisms of the same or different
species attempt to use an ecological
resource at the same place and the same
– Resource any necessity to life
– Plants and animals compete
– Winner and losers
• Interspecific competition
– Competition between same two species
– When 2 or more species rely on same limited
resource in a community
– Ex. African savannah
Rules, rules, rules
• Fundamental rule in ecology
– Competitive Exclusion Principle
• Russian biologist G.F. Gause
– Paramecium caudatum vs. Paramecium aurelia
• 2 species so similar in requirements that the same
resource limits both population’s growth, and one
species may succeed over another
• No two species can occupy the same niche in the
same habitat and the same time
• Prevents competition
• Each species unique living arrangement in
a community
• “Role”
• Ex. Lizards in a rainforest
• Includes:
– Habitat
– Food sources
– Time of day organism is most active
• Interaction where an organism captures
and feeds on another organism
• Predator
– Organism that does the killing and eating
• Prey
– Organism that is being killed and eaten
Predator Adaptations
Coloring/camouflage to ambush prey
– Ex. Wolves
• Acute senses
– Ex. Rattle snake heat sensor organs
• Claws, teeth, fangs, stingers, poison
Prey adaptations
Safe locations
Coloring/camouflage to hide
Defensive coloration
– “warning coloration”
• Mimicry
– Organisms imitate dangerous organisms by
appearance and actions
• Hawk moth larva
• Plants
– Thorns, spines, poisonous chemicals
• Any relationship where
two species live closely
• Symbiosis literally
means “living together”
• 3 main types
– Parasitism
– Mutualism
– commensalism
What type of relationship is this?
• Who is helping who?
• Both species benefit
from the relationship
• A Happy couple
• Flowers and bees
– Flowers need bees for
pollination, bees need
flowers nectar
What type of relation ship is going
on here?
• Who is helping who?
• One member of the relationship benefits
while the other is neither harmed nor
• One-sided
• Food or shelter
• Barnacles on whale
Ants and aphids
What type of interaction is going on
• One organism lives on or inside another
organism and harms it
• Parasite obtains all or part of its nutrients from
the other organism
• Host
– Organism that is harmed in relation ship; the one that
provides the nutrients to the parasite
• Parasite
– Organism that gets its nutrients from the host
• Do they want to kill their host?
– No, because they need them…they will weaken or
hurt the host in some way
What Is a Population?
In biology, a population is a group of organisms
of the same species that live in the same area.
How large a population is and how fast it is
growing are often used as measures of its
Population Growth Rate
• Population growth rate (r) is how fast a
population changes in size over time. A
positive growth rate means a population is
increasing. A negative growth rate means
it is decreasing. The two main factors
affecting population growth are the birth
rate (b) and death rate (d).
Births and Deaths: Balancing Costs
of Reproduction and Survival
• growth rate = birth rate – death rate
Other Factors Affecting
Population Growth Rate
Population growth may also be affected by
people coming into the population from
somewhere else (immigration, i) or leaving
the population for another area (emigration,
e). The formula for population growth takes
all these factors into account.
• r = (b + i) - (d + e)
r = population growth rate; b = birth rate; i = immigration
rate; d = death rate; and e = emigration rate
Patterns of Population Growth
• At first, exponentially then logistically until
carrying capacity is reached
After 5 hours of exponential growth;
one bacteria yields…
Limits to Population Growth
• limiting factor is a property of a
population’s environment – living or
nonliving – which controls the process of
population growth. Biologists have
identified two major types of limiting
– Density-dependent factors
– Density-independent factors.
What Is a Community?
Communities are made up of populations of
different species. A community is the biotic part
of an ecosystem. It consists of all the
populations of all the species in the same area.
It also includes their interactions.
What Is an Ecosystem?
An ecosystem is a unit of nature and the focus
of study in ecology. It consists of all the biotic
and abiotic factors in an area and their
interactions. Ecosystems can vary in size.
A lake could be considered an ecosystem. So
could a dead log on a forest floor. Both the lake
and log contain a variety of species that interact
with each other and with abiotic factors.
Ecosystem Components
• Niches
• Habitats
• Competitive Exclusion Principle
The Niche
Niche organism’s occupation (role), where it
lives, and way in which organism’s use
conditions they exist in
– Food it eats
– Place in food web
– How it gets food
– Range of temperatures
needed for survival
– When and how it
The Habitat
• Physical environment to which an
organisms has become adapted and
survives in.
Competitive Exclusion Principle
• Two different species
cannot occupy the
same niche in the
same geographic area.
If they do they will compete
with one another for the
same food and other resources.
Eventually, one species will
out compete the other.
What Are Biomes?
A biome is a group of similar ecosystems
with the same general abiotic factors and
primary producers. Biomes may be
terrestrial or aquatic.
Terrestrial Biomes
Terrestrial biomes include all the land areas
on Earth where organisms live. The
distinguishing features of terrestrial biomes
are determined mainly by climate (abiotic
factor). Terrestrial biomes include tundras,
temperate forests and grasslands,
chaparral, temperate and tropical deserts,
and tropical forests and grasslands.
Terrestrial Biomes and
• Climate is the average weather in an area over a
long period of time. Weather refers to the
conditions of the atmosphere from day to day.
• In terms of moisture, climates can be classified
as arid (dry), semi-arid, humid (wet), or semihumid. The amount of moisture depends on both
precipitation and evaporation.
• Biomes are categorized based upon their
climate types.
Climate and Biodiversity
Climate determines plant growth, it also
influences the number and variety of other
organisms in a terrestrial biome. Biodiversity
generally increases from the poles to the
equator. It is also usually greater in more
humid climates.
Climate and Adaptations
Organisms evolve adaptations that help them survive in the
climate of the biome where they live. For example, in biomes
with arid climates, plants may have special tissues for storing
water. The desert animals also have adaptations for a dry
climate. In biomes with cold climates, plants may adapt by
becoming dormant during the coldest part of the year.
Dormancy is a state in which a plant slows down cellular
activities and may shed its leaves. Animals also adapt to cold
temperatures. One way is with insulation in the form of fur and
Survey of Terrestrial Biomes
Terrestrial biomes are classified by climatic factors
and types of primary producers.
Aquatic Biomes
Terrestrial organisms are generally limited by temperature
and moisture.
Therefore, terrestrial biomes are defined in terms of these
abiotic factors.
Most aquatic organisms do not have to deal with extremes
of temperature or moisture.
Instead, their main limiting factors are the
availability of sunlight and the
concentration of dissolved oxygen
and nutrients in the water.
Aquatic Biomes and Sunlight
In large bodies of standing water, including the ocean and lakes, the water
can be divided into zones based on the amount of sunlight it receives:
1. The photic zone extends to a maximum depth of 200 meters; enough
sunlight penetrates for algae and other photosynthetic organisms to
2. The aphotic zone is water deeper than 200 meters; too little sunlight
penetrates for photosynthesis to occur. As a result, food must be made by
chemosynthesis or else drift down from the water above.
Aquatic Organisms
Aquatic organisms generally fall into three broad groups: plankton, nekton, and
benthos. They vary in how they move and where they live.
1. Plankton are tiny aquatic organisms that cannot move on their own. They live in
the photic zone. They include phytoplankton and zooplankton. Phytoplankton are
bacteria and algae that use sunlight to make food. Zooplankton are tiny animals that
feed on phytoplankton.
2. Nekton are aquatic animals that can move on their own by ‘‘swimming” through the
water. They may live in the photic or aphotic zone. They feed on plankton or other
nekton. Examples of nekton include fish and shrimp.
3. Benthos are aquatic organisms that crawl in sediments at the bottom of a body of
water. Many are decomposers. Benthos include sponges, clams, and anglerfish
which are adapted to a life in the dark.
What Is the Biosphere?
The biosphere is the global sum of all ecosystems; integrating
all living beings and their relationships, including their
interactions with the elements of the lithosphere, hydrosphere,
and atmosphere.
•What is community?
•What is population?
• What are the three types of interactions in
a community?
– Competition
– Predation
– Symbiosis
• What types do we have?
– Mutualism
– Commensalism
– Parasitism
Ecological Succession
• Do all ecosystems stay the same all the
• What are some things that cause changes
to ecosystems?
– Natural and unnatural
– Quickly and slowly
• Ecosystems are constantly changing in
response to human and natural
• As an ecosystem changes, older habitants
die out and new organisms move in,
causing more change
Ecological Succession
• Series of predictable changes that occur in
a community over time
– Physical environment
– Natural disturbance
– Human disturbance
Primary Succession
• Succession on land
that occurs on
surfaces where no
soil exists
• Volcanic eruptions
• Glaciers melting
Stages of Primary Succession
• Start with no soil, just ash and rock
• First species to populate this area
– “pioneer species”
– For example, pioneer species on volcanic
rock are lichens (LY-kunz)
• Lichens made up of fungus and algae that can
grow on bare rock
• When lichens die, they for organic material that
becomes soil…now plants can grow
Secondary Succession
• Succession following a disturbance that
destroys a community without destroying
the soil
• Natural
– hurricane
– fires
• Human disturbances
– Farming
– Forest clearing
Succession in Marine Ecosystems
• Deep and dark
• Can succession happen?
• 1987 dead whale off of California
– Unique community of organisms living in
– Represents stage in succession in an
otherwise stable, deep-sea ecosystem
– Whale-fall community
Whale-Fall Succession
• Begins when large whale dies
– Sinks to barren ocean floor
– Scavengers and decomposers flock to carcass , our first community
• Amphipods
• Hagfish
• sharks
• After a year, most tissues have been eaten
– Now, second small community of organisms live here
– Body is decomposing, releasing nutrients into the water
Small fishes
• Only skeleton remains…
– Third community moves in
• Heterotrophic bacteria
• Decompose oil in bones release of chemical compounds
• Who uses these chemical compounds?
– Chemoosynthetic autotrophs
• In come the crabs, clams, and worms that feed on this bacteria
Human Activity and Species
• Land clearing
– Farmland
– Diverse forest replaced with single crop
– Decreases species diversity
• Introduced species
– Humans move a species from its native land
to a new location, intentionally or accidentally
Chapter 35,
Ecology and