Download Ecosystem Interactions

1.3 INTERACTIONS IN
ECOSYSTEMS
pp. 36 - 42
LEARNING GOALS

By the end of this lesson, you should:
Understand the three different symbiotic
relationships
 Know what a predator – prey relsationship is and
why they are important
 Know what competition is and what the two types of
competitive relationships are
 Understand the concept of equilibrium and how
limiting factors contribute to creating it (e.g. carrying
capacity)

BIOTIC INTERACTIONS

Organisms in a community interact with one
another in many ways. Three main ways are
through symbiosis, predation, and competition.
SYMBIOTIC RELATIONSHIPS (3 TYPES)

Symbiosis is a close interaction between two
different species in which members of one species
live in, on, or near members of another species.
1. Commensalism
 + / 0 relationship
 One partner benefits without significantly
affecting the other

Example – Clown fish and anemone
SYMBIOTIC RELATIONSHIPS (3 TYPES)
2. Mutualism
 + / + relationship
 Both organisms benefit

Example – Bees and flowers, crocodiles and dikkop birds
3. Parasitism
 +/ - relationship
 One organism, the parasite, harms the host

Example – Deer, tick
PREDATOR – PREY
RELATIONSHIPS

When one organism consumes a second
organism
 Example – Lions and Zebras
 Some species use mimicry to avoid predators

one species looks like another species.
Monarch butterfly
Viceroy Butterfly
COMPETITIVE RELATIONSHIPS (2 TYPES)

Where organisms compete for an important
resource such as food, shelter or possibly mates.
 May have negative effects on one another.

Actual fighting or exploitative competition
1. Intraspecific
 Between members of the same species
 Individuals may compete over food, water,
light, space, safe sites, or mates.
 Important factor limiting the population
size of many species.
COMPETITIVE RELATIONSHIPS (2 TYPES)
2. INTERSPECIFIC
2. Interspecific
 Between 2 or more species
 As the population of one species increases, it
may limit the density of the competing species
CHARACTERISTICS OF POPULATIONS
As populations grow the resources available to
each individual gets smaller.
 When resources are decreased the number of
births will decrease and the number of deaths
will increase.
 Eventually the number of births will equal the
number of deaths.


This is called an equilibrium.
LIMITING FACTOR

Limiting Factor - Environmental factor that
prevents an increase in the number of organisms
in a population or prevents them from moving
into new habitats.
LIMITING FACTOR
 Abiotic

Sunlight, water, soil, and air, natural disturbances
such as storms, fires, droughts, and logging.
 Biotic

Limiting Factors
Limiting Factors
Competition among organisms for resources,
presence of predators, reliance on other organisms for
survival, and the presence of disease causing
organisms.
CARRYING CAPACITY
 The
maximum number individuals that
an ecosystem can support without
reducing its ability to support future
generations of the same species.

Exceeding the carrying capacity hurts the
environment.
CARRYING CAPACITY
The figure shows a rabbit population after it was
introduced to an ecosystem.
 At first the population grows quickly and then it
slows down to the point where the number of
births equals the number of deaths.

LEARNING GOALS

By the end of this lesson, you should:
Understand the three different symbiotic
relationships
 Know what a predator – prey relsationship is and
why they are important
 Know what competition is and what the two types of
competitive relationships are
 Understand the concept of equilibrium and how
limiting factors contribute to creating it (e.g. carrying
capacity)

HOMEWORK

Read pp. 36 – 42

Answer the following questions:
p. 42 # 1, 3
 p. 46 # 1 – 4, 7
