EEB 2244 Lecture 10: Population Distribution and Abundance
22 Dec 2018
School
Department
Course
Professor
Population Distribution and Abundance
Spatial Ecology
Spatial ecology is a specialization in ecology and geography that is concerned with how
ecological events can be explained through the detection of patterns at a given spatial scale.
Scale refers to the spatial extent of ecological processes and the spatial interpretation of
the data.
Organism’s response to the environment is particular to a specific scale and may
respond differently at a larger or smaller scale.
Choosing a scale that is appropriate to the ecological process in question is very
important to coming up with accurate hypotheses and proposing underlying causes for
observed patterns.
Spatial Scaling
The items determining a species existence at each of the levels is likely to be different.
• Global: Climate and evolutionary history, such as plant daylight hours, seasonal
minimums and maximums rainfall, historical extent and dispersal.
• Biome: life form overlaps, soil and climate, nutrient cycling, pollinators, seed
dispersers, shade, mutualists and their abiotic requirements
• Regional: human influences, topography, disturbances, fires earthquakes floods,
patchiness, proximity to major water source, mountain landscape, elevation
• Landscape: resource availability, community,
• Local small-scale topography and life forms: local nutrients availability, shade,
sunlight, water, presence of individuals of other species needed.
Spatial Structure
Populations have a spatial structure from global population to collections of populations
that interact through immigration and emigration, to a single population, to the spacing of
individuals within that population.
The patterns reflect vital rate-related processes (survival/mortality, reproduction) and
the landscape’s influence.
At each level there are areas that are suitable or not, preferable or not.
Global range – limits of where organisms may be found geographical. Populations often
do not exist in every region within this range.
Metapopulations – group of populations that are separated by space but consist of the
same species.
Social groups with-in the population start to divide by function.
Niche and Distributions
Many of the attributes of a population distribution are impacted by the niche of the
organism in question.
Spatial distribution of populations is limited by their niche to ecologically suitable
habitats.
Measure niche as N-dimensional hypervolume: A region defined by more than three
dimensions, environmental conditions in which a population has positive growth.
3 Dimension Niche Representation:
• In layman’s terms: we are interested in
measuring the range of conditions where a
population performs well
• Can be impacted by interactions with other
species, such as competition.
Competitive Exclusion and Niches
Some of things impacting niches can be interactions with other organisms and
competition really comes in to play here.
In ecology, the competitive exclusion principle: states that two species competing for
the same resource cannot coexist at constant population values, if other ecological factors
remain constant.
When one species has even the slightest advantage or edge over another then the one
with the advantage will dominate in the long term.
One of the two competitors will always overcome the other, leading to either the
extinction of this competitor or an evolutionary or behavioral shift toward a different ecological
niche.
Maxim "complete competitors cannot coexist” which causes two different types of
niches in ecology.
Fundamental niche only takes the abiotic into account (climate, topography, soil, some
types of disturbance), range of abiotic conditions under which a species can exist.
Realized niche: the range of abiotic and biotic conditions under which a species can
exist. Takes the biotic into account. Is typically smaller than the fundamental niche. Considers
things like predators, competitors, mutualists
Classic study by Joseph Connell provides evidence of this in natural systems.
Competition with Balanus balanoides restricts the realized niche of Chthamalus
stellatus.
• Physically Chthamalus barnacle is capable of living
along the whole tidal range of the water.
• Balanus is not – it cannot tolerate drying out but is
heavier and faster growing and can push the other
barnacle off the rock.
• Balanus is therefore the stronger competitor and
restricts its niche of Chthamalus in the lower tidal
regions where desiccation is not such an issue.
• Balanus, therefore, restricts the realized niche of
Chthamalus.
Attribute 1: Geographic Range
Niche affects the geographic range of a population. Geographic range is a measure of
the total area covered by a species.
Reflects an organism’s realized niche translated onto a map.
Limited by:
• Abiotic Conditions
▪ Geographic ranges are limited by climate and other abiotic
conditions.
▪ Often get different conditions being important in different parts
of its range
▪ Geographic range of the sugar maple closely reflects its climatic
constraints – its realized niche and its fundamental niche are very
similar.
▪ Set of conditions containing all the areas suitable to a species is a
species’ climate envelope.
▪ Can contain areas that are occupied and areas that are
unoccupied (but still suitable)
• Habitat Availability
o Suitable climatic areas contain spaces where species are not present. A
geographic range is further restricted by the availability of suitable
habitats within that range.
o Environmental conditions caused by topography, and perhaps vegetation,
impacting soil, sunlight, water availability.
o Endemic: species that live in a single, often isolated, location.
Document Summary
Scale refers to the spatial extent of ecological processes and the spatial interpretation of. Spatial ecology is a specialization in ecology and geography that is concerned with how. Spatial ecology ecological events can be explained through the detection of patterns at a given spatial scale. the data. respond differently at a larger or smaller scale. Choosing a scale that is appropriate to the ecological process in question is very important to coming up with accurate hypotheses and proposing underlying causes for observed patterns. Organism"s response to the environment is particular to a specific scale and may. Populations have a spatial structure from global population to collections of populations. The patterns reflect vital rate-related processes (survival/mortality, reproduction) and. At each level there are areas that are suitable or not, preferable or not. Global range limits of where organisms may be found geographical.
