integrated lec 22 Flashcards
dispersal
Definition: Movement of individuals from one population to another.
Importance:
Colonization of New Areas: Enables species to expand their range (e.g., postglacial colonization after ice ages).
Escape from Competition: Reduces resource overlap and intraspecific competition.
Avoidance of Inbreeding Depression: Promotes genetic diversity.
Adaptations for Dispersal:
Seed Dispersal Mechanisms:
Animal-Driven: Fleshy fruits attract animal dispersers.
Wind/Water Dispersal: Adaptations like lightweight seeds (e.g., dandelions).
Examples:
Range shifts due to climate change.
Colonization of islands.
metapopulations
Definition: A collection of spatially distinct populations (patches) connected by dispersal.
Characteristics:
Populations in patches may go extinct but are “rescued” by immigrants from other patches.
Source-Sink Dynamics:
Source Populations: Stable populations that produce excess individuals.
Sink Populations: Populations that would go extinct without immigration from sources.
Importance:
Facilitates species persistence even when individual populations are unstable.
Promotes coexistence of species (e.g., competitors, predators, and prey)
How does dispersal contribute to metapopulation stability?
Key Idea: Dispersal enhances metapopulation stability by connecting local populations and reducing extinction risks.
How Dispersal Contributes:
1.Recolonization of Patches:
Dispersal allows extinct patches to be recolonized, maintaining overall metapopulation size.
2.Genetic Exchange:
Movement between patches prevents inbreeding and maintains genetic diversity.
3.Risk Spreading:
Dispersal distributes individuals across patches, reducing the risk of total population collapse due to localized disasters.
4.Population Rescue Effect:
Dispersers can bolster small or declining populations, preventing local extinction.
5.Spatial Synchronization:
Dispersal buffers fluctuations by balancing population sizes across patches.
Takeaway: Dispersal connects local populations, enabling recolonization, risk reduction, and genetic flow, ensuring long-term metapopulation stability.
Levin’s patch occupancy model
Overview: Describes dynamics of patch occupancy in metapopulations.
Key Variables:
P: Proportion of occupied patches.
c: Colonization rate.
e: Extinction rate.
Equation:
dP/dt: cP(1-P)- eP
At eq. … P=1 - e/c
Applications:
Explains persistence of species in fragmented habitats.
Demonstrates the balance between extinction and colonization rates.
Island Biogeography Theory
Founders: MacArthur and Wilson.
Goal: Predict species richness on islands based on size and isolation.
Processes:
Colonization: Species arrive from the mainland.
Extinction: Species go extinct due to limited resources or competition.
Speciation (slow): Lineages diversify on islands, but this is a minor factor in the model.
Key Predictions:
Larger islands support more species (lower extinction rates).
Closer islands have higher colonization rates.
Graphical Representation:
Colonization and extinction rates plotted against species richness.
Equilibrium point where colonization rate = extinction rate determines species richness.
Examples:
Anolis Lizards: Species richness increases with island size and decreases with isolation.
Habitat Fragmentation and “Island-Like” Habitats
Definition: Habitat fragmentation creates patches of suitable habitat surrounded by unsuitable areas, mimicking islands.
Effects:
Reduces species richness.
Increases extinction risk due to isolation and smaller habitat size.
Applications of Island Biogeography:
Predicts outcomes in fragmented landscapes.
Helps design nature reserves and corridors to enhance connectivity.
Metacommunities
Definition: A set of local communities linked by the dispersal of one or more species.
Key Features:
Builds on metapopulation theory by considering species interactions (e.g., competition, predation).
Promotes coexistence through dispersal and spatial heterogeneity.
Levin’s Model:
Describes patch dynamics using colonization and extinction rates
Habitat fragmentation creates “islands,” reducing ….
species richness.
MacArthur and Wilson:
Developed the theory of island biogeography.
Why is dispersal important for organisms?
A: It allows colonization of new areas, reduces competition, and prevents inbreeding depression.
How does dispersal facilitate range shifts?
A: It allows species to track suitable habitats in response to climate change.
Why is dispersal critical in postglacial colonization?
A: It enables species to recolonize areas previously covered by ice.
Define metapopulation.
A: A collection of spatially distinct populations connected by dispersal.
What is the role of dispersal in metapopulation dynamics?
A: It rescues local populations from extinction and promotes population stability.
What are source populations?
A: Populations that produce excess individuals who can colonize other patches.
What are sink populations?
A: Populations that would go extinct without immigration from source populations
How do source-sink dynamics promote species persistence?
A: Migrants from source populations sustain sink populations that cannot survive independently.
What does Levin’s patch occupancy model describe?
A: The dynamics of patch occupancy in a metapopulation
What happens to P when c>e?
A: The metapopulation persists because colonization exceeds extinction.
How does increasing c affect patch occupancy?
A: Higher colonization rates increase the equilibrium fraction of occupied patches
What is the theory of island biogeography?
A: A model predicting species richness based on island size and isolation.
What are the main processes influencing island species richness?
A: Colonization, extinction, and (less commonly) in-situ speciation
How does island size affect species richness?
A: Larger islands support more species due to lower extinction rates.
How does island isolation affect species richness?
A: Closer islands have higher colonization rates, leading to greater species richness.
How does habitat fragmentation create “islands”?
A: It creates patches of suitable habitat surrounded by unsuitable areas.
Why is habitat fragmentation problematic for species?
A: It reduces species richness and increases extinction risk due to smaller patch sizes and isolation.
How can island biogeography theory be applied to fragmented habitats?
A: It predicts species richness based on patch size and connectivity.
How do fragmented habitats mimic island systems?
A: Isolated patches function like islands, with colonization and extinction dynamics.
How do metacommunities differ from metapopulations?
A: Metacommunities focus on interactions between species across patches, not just single species dynamics
How does dispersal promote coexistence in metacommunities?
A: It allows species to escape competition and recolonize patches after local extinction
What is the competition-colonization trade-off?
A: Better dispersers can persist in patches despite being outcompeted locally by superior competitors.
Why are non-equilibrial conditions important for species coexistence?
A: They prevent competitive exclusion by maintaining dynamic patch occupancy.
Give an example of metapopulation persistence.
A: Pikas in Bodie, California, occupy tailings piles (patches) where dispersal balances extinction and recolonization.
Give an example of a competition-colonization trade-off.
A: A fugitive species (B) can persist in patches by dispersing better than a superior competitor (A).
