Lecture 19 Flashcards
1
Q
Why are organisms where they are?
A
slide 4
2
Q
Ranges & Distributions
A
- Range: the spatial extent of a
species - Distribution: the spatial extent of a
population - Individuals do not occupy the entire
distribution because not all areas
are suitable habitat - Species with extensive geographic
distribution typically encounter a
wider range of environmental
conditions and are generalists
slide 5
3
Q
Ranges & Distributions
A
slide 6-7
4
Q
Endemism
A
- Endemism: Small restricted
geographic ranges; found in a
location and nowhere else - Constrained by isolation
and/or narrow habitat
requirements - Often of conservation concern
- Often on islands
slide 8
5
Q
Range Expansion
A
- Range size can change over time with shift in climate, resources, change in
competitors or predators, or introduction
slide 9
6
Q
Evolutionary Implications of Distributions
A
- Isolation & dispersal influence
migration and gene flow - Migration reduces population
differentiation - Range size impacts genetic drift
- Allele frequency changes as a
result of random chance more
common in small populations - Ecological conditions (biotic
and abiotic features of the
ecosystem) influence the
strength and nature of natural
selection
slide 10-11
7
Q
The Ecological Niche
A
- Ecological niche: the range of
environmental conditions and
essential resources needed for
a species to survive and
reproduce - Conditions must fall within an
organism’s environmental
tolerance for it to persist - Organismal traits are related to
their environment: they
determine where they will
thrive as well as limit where
they can exist - Each combination of
environmental conditions
present unique constraints on
organisms - Adaptations allow species to
thrive under a specific set of
environmental conditions - These conditions reflect
requirements and adaptations: - Physiological
- Morphological
- Behavioral
slide 13-14
8
Q
The Ecological Niche
A
- Developed by Joseph Grinnell
and Charles Elton in 1920’s - Grinnell focused on habitat and
the limitations of the physical
environment - Elton emphasized species
interactions - G. Evelyn Hutchinson: niches are
multidimensional!
“N-dimensional hypervolume” - Each axis is a variable relating to
resource needs or environmental
constraints
slide 15-17
9
Q
Fundamental Niche
A
- Fundamental Niche: the range of
environmental conditions tolerated by
a species - Describes the potential habitat space
of an organism and constraints on
where it can be found based on
environmental conditions - Each species has limits beyond which
it cannot survive - As environmental conditions change in
time and space, potential distribution
changes
slide 18
10
Q
Realized Niche
A
- Realized Niche: the actual habitat
occupied by a species as a
consequence of species interactions
and barriers to movement - The realized niche is a subset of the
fundamental niche - Describes the actual habitat space of
an organism based on where it has
been found - Reflects the abiotic constraints
(environmental tolerance) AND biotic
interactions
slide 19-20
11
Q
Quantifying Niche Space
A
- Ecological niche
models (also known
as bioclimatic
envelope model,
species distribution
model) relate
climate to known
distribution - Results of model can be used to map potential geographic distribution under
past, present, and future conditions
slide 21-24
12
Q
Realized Niche: Species Interactions?
A
- Species interactions shape the
realized niche too! - Negative interactions
(competition, predation, disease)
can limit the realized niche - Positive interactions
(commensalism, mutualism) can
modify the fundamental niche by
directly or indirectly enhancing
survival and reproduction of
other species - Species interactions also interact
with the abiotic environment
slide 25
13
Q
Realized Niche: Overlap
A
- Competitive exclusion principle: two species cannot coexist if they occupy
exactly the same niche (competing for identical resources) - The resource gradient will be divided among the species to minimize overlap
- Species may evolve to reduce niche overlap resulting in niche partitioning and
increasing specialization
slide 26
13
Q
Niche Partitioning
A
- Each species exploits a
portion of resources
unavailable to others - Niche space can be
divided: - Spatially: where the
organism physically is - Temporally: when the
organism uses the habitat - Behaviorally: what the
organism consumes (diet,
resources, light, nutrients)
slide 27
14
Q
Competitive Exclusion
A
- Species distributions can be restricted by
physiological tolerance and competition - Zonation results from exclusion by a
dominant species
slide 28
15
Q
Niche Partitioning – Competitive Exclusion
A
- Elevation creates different
ecological niches
characterized by
temperature, vegetation
type, and food resources - Example: Different species
of chipmunks occupy
different altitudinal zones
because of a combination
of thermal tolerance and
competitive exclusion
slide 29
16
Q
Character Displacement
A
- When niche partitioning involves
phenotypic adaptation
(morphology, behavior, physiology)
directional selection leads to
character displacement
slide 30
17
Q
Niche Partitioning – Character Displacement
A
“Ghost of competition past” when character displacement is presumed to
have occurred in the past to lead to present day niche partitioning
slide 31
18
Q
Habitat Heterogeneity
A
- Resources are not usually
homogeneous in an environment - Increasing environmental variation
(heterogeneity) typically results in
increasing beta diversity as species
are restricted to subsets of the
habitat - This means more unique species
- Environmental variation supports
higher phenotypic (and by extension
genetic) variation for natural
selection to act on - More habitat = more species!
- Habitat heterogeneity produces different types of niche space to occupy
allowing more species with narrow niches to fit - Most species will be specialists, few will be generalists because of competitive
exclusion - Sources of habitat heterogeneity:
- Disturbance (e.g., treefall)
- Vertical structure (forest)
- Elevation
- Land cover
- Patterns of nutrients and microclimate
- Variation in food resources
- Seasons
- Habitat
heterogeneity
facilitates niche
partitioning - Species niches
become more
narrow - Species become
more specialized - More specialized
species are more
likely to have
restricted ranges
(endemic)
slide 32-34
19
Q
Eco-Evolutionary Relationships
A
Evolutionary ecology
focuses on identifying
phenotypes (traits) that are
ecologically important and
understanding how and
why those traits vary in
different environments
slide 35
20
Q
Environmental Gradients: Clines
A
- Clines are measurable, gradual changes in a
phenotype (trait) associated with a continuously
varying environment - Environmental variation creates variation in
natural selection across a species distribution - Gene flow along the environmental gradient
maintains continuous phenotypic variation - Example: Along an elevational gradient
precipitation and temperature decrease with
altitude. This produces a continuous variation of
phenotypes correlated with altitude in
Arabadopsis thaliana.
slide 36
21
Q
Environmental Gradients: Ecotypes
A
- Clinal variation may not transition smoothly from one habitat to an adjacent
habitat if the environment abruptly changes - Ecotypes are populations adapted to
unique local conditions with differences
maintained by natural selection
slide 37
22
Q
Phenotypic and Environmental Variation
A
- Phenotypes (traits) are influenced
by the environment - Because the environment is
variable in space and time,
phenotypes are variable - Phenotypic plasticity can influence
trait variation within a generation
– the same genotype produces
different phenotypes depending
on the environment - Adaptation can influence trait
variation across generations
through natural selection
slide 38
23
Q
Adaptation: Trait-Environment Relationships
A
- Adaptations are tightly linked to the ecological
niche - Adaptations increase fitness of an individual under
a given set of environmental conditions - Environment imposes constraints on processes
related to fitness: survival, growth, reproduction - How adaptations enable an organism to thrive in
one environment and not in another is key to
understanding the distribution and abundance of
species. - Adaptations arise because of the interaction of
individuals with their environment leading to
differential survival and reproduction (natural
selection) - Environment: selective landscape
- Trait: selective target
- Environmental change: selective agent
slide 39
24
Adaptation: Trait-Environment Relationships
* MANY types of adaptations that
correlate with niche
* Across the tree of life all organisms
must first be able to tolerate the
abiotic environment
* Physiology related to abiotic
conditions (thermal tolerance and
desiccation tolerance) are strongly
tied to distribution
* Diet specialization and crypsis are
other common environmentally
correlated traits in animals
slide 40
25
Plant Adaptations: Temp. & Precipitation
* Leaf area and shape relate to heat dissipation
* In habitats with abundant water, larger leaves are more effective at cooling via evapotranspiration
* In habitats with little water, smaller leaves are more effective at cooling via convection
* Leaf characteristics reduce light absorption and water loss: thick cell walls, hairs, waxy
coating
* Water availability influences roots vs leaves investment
* More water = more leaves, less water = more roots
* Cold is a problem too! Anti-freeze compounds protect plants (at a cost to the plant)
slide 41
26
Animal Adaptations: Temp. & Precipitation
* Behavioral:
* Migration
* Burrowing
* Diapause (arrested development in
insects)
* Nocturnal activity
* Movement between sun / shade / water
* Physiological:
* Water extraction from food, concentrated
wastes
* Shivering, panting, sweating
* Dormancy (estivation, hibernation) &
torpor
* Heat storage / night dissipation
* Supercooling protection from freezing
* Morphological:
* Fur, feathers, fat
* Coloration
* Vascular modifications
slide 42
27
Darwin’s Finches
slide 43
28
Key Points to understand
* What factors shape where organisms are where they are?
* What is an endemic species?
* What is an ecological niche? How does the realized niche
differ from the fundamental niche?
* What does modelling niche space tell us (what is it used for)?
* How do disturbance and species interactions modify niche
space?
* How does distribution and niche space relate to adaptive
(natural selection) and nonadaptive (genetic drift) evolution?
* What is the relationship between habitat variation and
species diversity?
* What key adaptations and plants and animals are closely tied
to niche space?
* How does the ecology and evolution of Darwin’s Finches
illustrate each of the concepts above?
slide 44
