TOPIC 9: SPATIAL POPULATION STRUCTURE Flashcards
Population
A group of individuals of the same species living together
Population Ecology
How the processes of birth, death, migration influence the abundance & distribution patterns
of groups of organisms
How is pop. structure characterized?
- Spatial Structure
- Age/Size Structure
- Genetic Structure
Spatial Structure
how individuals organize themselves in space
* geographic distribution/range
* patterns of dispersal
* patterns of dispersion
* population size (# of indiv. that make up pop within that range)
Age/Size Structure –
– number of individuals in each age/size class
* demographic rates (b, d, migration) of individuals change throughout their
lifetime
Genetic Structure
genetic composition of all individuals combined within the population
- more diff alleles more structure genetic structure will be
- Geographical distribution/range
= geographical area in which a species occurs
* where they can be found on earth
what is Geographical distribution determined by?
determined by presence of suitable environmental conditions & resources
- Habitat patch
area of homogeneous environmental conditions
* contains suitable conditions and resources needed to sustain a population
*indiv can group themselves within habitat patches moving between patches= dispersal
(subpopulation)
- Habitat patches can be heterogeneously distributed over the range, separated by
unsuitable habitat
results in many local populations of a species within a range
(subpopulation) - when talking abt pop. we talk abt subpop
- when looking at genetic structure we need to consider all subpop. together b/c they could be interbreeding
- Devil’s Hole Pupfish
- Exists in a single desert pool in Death Valley, Nevada
- 7 x 3 m and 15 m deep
- only exist within this pool so range is very small
Describe the distribution of Coyotes, Norway Rats, E. Coli and Whales
- Coyotes over most of North America
- Rats and E. Coli spread with human movements; range is enormous
- Whales are very large migratory species with a lot of “ground” to cover
What is range based on?
- Based on historical and recent human observation; DOESNt mean species doesn’t exist if we’ve never seen it (could exist out of its range) or if we saw it there once doesn’t mean it will still exist there due to changes in envri. conditions like habitat destruction
- Range limitations are a malleable construct as environmental conditions shift
- Just because ideal conditions exist does not mean you will find a species there
- Must account for the colonization abilities of ancestral species; need to consider whether or not ancestral pop. were able to migrate to those areas
- Why are there no polar bears in Antarctica?
What causes most population to be divided into subpopulations ?
environmental heterogeneity; conditions are diff in diff areas across diff scales
Each subpopulation exists in a suitable habitat and is separated from other
subpopulations by unsuitable habitat
- Metapopulations
are the collective of all subpopulations
* Ecology typically occurs at the level of the subpopulation rather than the entire
population over its entire geographic range
dispersal
Movement of individuals in space
= movement of individuals away from place of birth or areas of high population
density
indiv will be born in a habitat patch and then move to a diff patch
At some stage in their life or life cycle most organisms are mobile
Movements of individuals directly influences…
their local density
* affects evolution within subpop.
Movement of individuals among the subpopulations is key to the dynamics of
metapopulations
How do animals disperse?
With animals dispersal is active but many use passive means like wind and water
- Wind carries the young of spiders and moths
- Larval forms of many invertebrates are carried downstream by currents
How do plants disperse?
Plants tend to move at the level of seed
* Dispersal of seeds involves gravity, wind, water and animals
- Plants that have adaptations designed for increased dispersal
- Release of fluid pressure allows some plants to physically eject seeds a
considerable distance - Buoyancy allows fruits/seeds to be carried away by water
- Other plants use sugar rewards to attract herbivores
- Incentive to consume the fruit and transport seeds to another location
- Seeds pass unharmed though the digestive tract
- Fruits and seeds armed with hooks and spines to catch on the fur on animal; use animal dispersal for own dispersal
Emigration
movement of individuals out of a population
Emigration
movement of individuals out of a population
Immigration –
– movement of individuals into a population
How are emigration and immigration linked?
every emigration= immigration
- when they move out of a pop they also move into a new pop
What does the degree of interaction among local populations depend on?
- Ability of individuals to disperse between habitat patches
- Habitat patch size and quality
. Ability of individuals to disperse between habitat patches:
- distance between habitat patches
- suitability of environmental conditions & resource abundance between patches; like going on a road trip in arctic there’s no gas stations make sjourney hard whereas if you pass small towns with gas stations it makes the journey easier
- barriers (e.g. mountain, ocean)
Habitat patch size and quality
- larger/higher quality patches tend to support more individuals
- a higher number of individuals immigrate to smaller/lower quality local
populations with fewer individuals
Dispersion
Where geographical distribution refers to the extent of a population, patterns of
dispersion can also be used to describe the spatial position of one individual to another
- how indiv. within a sub pop. orient themselves within a patch
List the different types of dispersion patterns
Random
Uniform
Clumped
Random
- Individuals have no influence on each other
- Resources are randomly scattered across the range
- not seen in nature, happens when there’s no benefit to clumping so random
- used as a control
Uniform
Individuals engage in negative interactions, such as intense competition for
space
- Individuals space themselves evenly to minimize interactions
plants ex; competition for light
animals try to get as much space as for themselves
Clumped
- Most common type of distribution, where individuals form groups/clusters
- Patchy resource distribution or environmental conditions
- Social tendencies; protection from predators
- Cloning
Describe the dispersion pattern of the Northern Gannet
Critical to define the spatial scale of dispersion patterns
Large scale:
Clumped (breeding habitat)
Moderate scale: Clumped
(predator avoidance)
Small scale: Even (competition)
What is an Individual?
- Population = a group of individuals of one species living together
- represent the ecological unit within which individuals mate and offspring are
produced
What are the 2 types of individuals can make up a population?
- Unitary Individuals –
- Modular Individuals
Unitary Individuals
physically and genetically distinct individuals each arising
from a genetically distinct zygote (e.g. humans, dogs)
- have to be physiologically distinct
are genets
genets
genetically distinct individuals, each derived from a single zygote
(sexual reproduction)
come from own zygote genetically distinct
- Modular Individuals
– consist of many interconnected units derived from the
same zygote (e.g. plants, corals, sponges)
* Modular individuals can exist separately and be physiologically
independent
* arisen thru asexual repro so genetically identical
ramets
ramets
Modules with the potential to exist separately
genetically identical; asexual reproduction come from same zygote
Aspen tree
- a tree develops from a seed (zygote); genet
- reproduces asexually via underground horizontal roots; ramet
- gives rise to what appears to be another individual tree
- Each tree produced is a ramet, while all trees together are a genet; ALL THE TREES TOGETHER ARE 1 SINGLE GENET
Why is it distinguish between unitary (genetically distinct) and modular (genetically
identical) individual?
- remember… must be genetic variation for natural selection to occur
Conservation: if a population of ramets → no genetic variation → less likely to adapt to
environmental changes → high risk of extinction
What do Accurate estimates combine?
- Geographical range; area which we can look for species
- Patterns of dispersion
Local density (=# of individuals per unit area)
Patterns of dispersion of local population density can mislead measures of total
population size
List the diff methods of Estimation
- Quadrat Sampling
Line Transects - Mark-Recapture
- Quadrat Sampling
- Previous example(LOOK AT NOTES)
- Best on sessile/immobile organisms
make smaller squares within a big area and multiply thru
Line Transects
Measure distance to observed specimens while walking a straight line
* Use of formulas to estimate pop. size
- Mark-Recapture
Create an identifiable mark on all specimens captured in first sample
- Sample again and estimate pop. Size based on the proportion recapture
