Friday, October 19 th : Period E
• 1. An update on EXCEL 2011
• 2. Homework Review
• 2. Completing Topic G.1, Community Ecology

EXCEL – Revised, Improved
Worksheet…
• Please complete your temperature assignment by
Tuesday. The worksheet (revised for EXCEL 2010) is accesible on the Class Blog
• Please contact me if you don’t have access to
EXCEL, or if you need some help
• Use your IB Independent Assessment Guide – it has all of the answers to your questions!!
• Online help:
• Getting started with EXCEL

Homework Review: Factors
Affecting Plant and Animal Species
Distribution

i-Biology Link

i-biology hyperlink

Homework Review: Relationships
Between Species

Relationships Between Species
RELATIONSHIP
HERBIVORY
PREDATION
PARASITISM
MUTUALISM
(COMMENSALISM)
COMPETITION
SPECIES 1
Plant: +/-
Predator: +
Host: -
Species 1: +
Species 1: 0
+/-/0
SPECIES 2
Primary Consumer +
Prey: -
Parasite: +
Species 2: +
Species 2: 0
+/-/0

Let’s Check those relationships…
• It's David....(3.30)
• National Geographic Anemones/clownfish
• PBS marine interactions
• Marine Mutualism

COMPLETING Topic G:1
•
•
•
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When does it happen?
• Shared resource in short supply
• Competion is a density dependent determinant of population dynamics
Do competitors have to meet each other?
Competition can be between individuals of the same species
(intra-specific) or between different species
(interspecific)

Intra-specific competition:
Competition for mates
• Male Bighorn Sheep
• Bisons headbutting

Intra-specific competition: Darwin’s
Finches
• Darwin's Finches

Interspecific Competition
Competition between different species which depend on the same resource:
• Food
• Water
• Nesting Sites
• Breeding Sites
Examples:
Competition...in spades...

The Niche Concept
Topic G.1.5: Explain what is meant by the niche concept, including an organism’s spatial habitat, its feeding activities and its interactions with other species

The Niche Concept: Definition
‘Nicher’ (French): to Nest
• A term describing the way of life of a population
• To describe a population’s niche, you need to describe its ‘specialised habitat’:
– space and territory
– Nutrition and feeding habits
– Interactions with other organisms
– Its reproductive habits
– Its role in the community

The Niche concept: A Working
Analogy
In 1927, Charles
Sutherland Elton, the
British Ecologist, stated:
‘When an ecologist states
‘There goes a badger’, he should include in his thoughts a definite idea of the animal’s role in the community, just as if he had said ‘There goes the vicar’

Defining a Niche : ‘The Boundary conditions’
Two species that use
exactly the same resources cannot occupy the same niche
Only one species or population can occupy the same niche for an extended period

Fundamental Niche
A species’ fundamental niche is the full range of environmental and social conditions under which it could potentially survive and reproduce
‘potential niche’
• Some species have a broad fundamental niche
• Some species have a narrow fundamental niche

Realised Niche
The realised niche is the specific set of conditions in which it survives in a given
habitat or ecosystem, given the other species or limitations present.
These are the conditions to which the population is best adapted.

‘Realised Niche’ is not a constant for a species
• In fact, populations of the same species may occupy different realised niches within different ecosystems
• It all depends on the other species and environmental factors involved in ‘sharing of the resources’

Let’s look at some examples….

G.F. Hutchinson’s Definition of the
Hyperdimensional Niche…

Homework for Monday
• Research information for two species of your choice.
• One can be the Clown-fish
• The other can come from the WWF website:
• WWF species directory

G.1.7: Explain the principle of competitive exclusion
Aka ‘Gause’s Law’
‘No two species can occupy the same
niche for a prolonged time’

The Competitive Exclusion Principle
• If two species share a niche, there must be interspecific competition for resources
• The best adapted species will survive
• The loser will struggle to survive and reproduce, and will eventually become extinct OR migrate (if its niche is broad enough)
Examples are abundant
• Invasive species
• Red versus Grey
Squirrel in Western
Europe
• Gause’s Paramecium

Competitive
Exclusion:
Squirrels

Competitive Exclusion: Squirrel
Distribution

G.1.7: Outline the method and importance of G.F. Gause’s paramecium experiments
Gause's Struggle for existence can be accessed in full online (even in Russian!)!

G.1.7: Outline the method and importance of G.F. Gause’s paramecium experiments
Georgy Gause cultured 2 species of the protist
Paramecium :
• P. Aurelia
• P. Caudatum
• Grown together under ideal conditions, both populations reach a higher maximum
• Grown together, one species rapidly becomes extinct…

Let’s think about it…..
How does environmental change affect a species with a broad niche?

Species with a broad niche
• ‘Generalists’
• Widely distributed geographically
• Adaptable
Red-Tailed Hawk

Let’s think about it…..
How does environmental change affect a species with a narrow niche?

Species with a narrow Niche
• ‘Specialists’
• Not adaptable
• Under threat of extinction if the niche changes

Does Competitive Exclusion work in the real world?....
The competitive Exclusion principle is actually rarely observed in natural ecosystems:
• ‘spatial heterogenity’ (niche partitioning)
• Niche sharing/ partitioning associated with availability of multiple resources
• ‘The paradox of the plankton’: Why do so many plankton species exist in a small, limited, homogenous habitat?

Niche Partitioning
As there is a limited about of space and resources on
Earth, organisms can use niche partitioning
1. Spatial: Two different species use the same resource by occupying different areas within the range of the resource
2. Temporal: Two species eliminate direct competition by using the same resource at different times
3. Morphological: Two different species evolve different morphologies in order to use a resource in different ways

Spatial Niche Partitioning
Closely related bird species occupy different foraging locations on a single tree species

Temporal Niche Partitioning
Different species of spiny mouse inhabiting the same ecosystem may be either nocturnal OR diurnal feeders

Morphological Niche Partitioning
Different beak sizes have allowed adaptive radiation of finches in the
Galapagos Islands