lecture 6: Spatial Population Structure Flashcards
(19 cards)
Types of Individuals in a Population: Unitary Individuals
Each comes from a different zygote (sexual reproduction).
They are physically and genetically distinct.
Example: Humans, Dogs.
These individuals are called genets (one zygote = one unique individual).
Types of Individuals in a Population: Modular Individuals
Come from the same zygote but reproduce asexually.
Made of interconnected units (can live separately).
Example: Plants, Corals, Sponges.
Example: Aspen Tree
One seed = one genet.
It grows and spreads via underground roots.
Each new tree is a ramet (clone).
All ramets together = one genet.
problem with ramets
if a population of ramets → no genetic variation → less likely to adapt to
environmental changes → high risk of extinction
Geographical Range, and what is it based on
the area on Earth where that species can be found.
It’s based on:
suitable environmental conditions & resources
Habitat Patch
A small area with homogeneous conditions for a species to live and reproduce.
Habitat patches may be:
Spread out across the range.
heterogenously distributed and Separated by unsuitable areas (e.g. deserts, oceans, cities).
-This leads to many small populations (called subpopulations) within the species’ overall range.
Range Limitations
A species’ range can change over time as:
Environmental conditions change (e.g. climate change).
Human activity changes landscapes or moves species around.
Note: Even if a place looks perfect, a species might not be there because:
Its ancestors couldn’t reach it (low colonization ability).
Something blocked its migration (e.g. no polar bears in Antarctica)
metapopulation
a group of local populations of the same species that are spread out in separate habitat patches, but still interact with each other through dispersal.
Think of it as a “population of populations.”
how do local populations interact
Through Dispersal
Dispersal = movement of individuals
Away from birthplace or high population density (emigration/immigration)
Metapopulation Size Depends On:
Size of each local population
Total number of individuals withing a local population and amoung all populations
Rescue Effect:
Individuals from good patches (source) move to bad patches (sink) and help maintain those populations.
Think of it like big cities sending people to support smaller towns.
How Much Local Populations Interact Depends On:
- Dispersal Ability
Can individuals move from one patch to another?
Distance between patches
Barriers (e.g., mountain, ocean)
Conditions between patches (is it safe)
- Habitat Patch Size & Quality
Large, high-quality patches support more individuals.
Dispersal in Plants
Happens through seeds:
Gravity
Wind (e.g., dandelions)
Water
Animals (via fur, feathers, or guts)=
plants adaptations for dispersal
Hooks to cling onto animal fur.
Fruit/sugar rewards to attract animals – seeds survive digestion.
Some plants shoot seeds using pressure!
Dispersal in Animals
Usually active movement (walking, flying, swimming)
Some use passive methods too:
Wind: baby spiders or moths float through the air
Water: larvae of aquatic animals drift with currents
3 patterns of dispersal
- clumped (due to heterogenous distribution of suitable conditions/resources)
- even (competitive interactions among ind)
- random (rare)
what influences dispersion patterns
Environmental conditions/resources influence dispersion patterns at different spatial scales
different methods to estimate population size
Quadrat Sampling
Best on sessile/immobile organisms
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 recaptured
Mark-recapture Assumptions:
- captures are random
- marks are not lost
- population is closed (no b, i)
- behaviour is not affected by marking (‘trap happy, shy’)
- marks do not cause higher mortality
