Lecture 31

Metapopulations consist of spatially isolated populations interconnected by dispersal.
- Source populations: Send out more migrants than they receive.
- Sink populations: Receive more migrants than they send out.
Example: Alaskan Muskeg serves as a source-sink model.

Different patches may exhibit varying growth rates.
Patches can go extinct and be recolonized, likened to "blinking lights" in population dynamics.
Metapopulation persistence condition: \frac{e}{c} < 1 where:
- $e$ = extinction rate
- $c$ = colonization rate
Factors affecting extinction and colonization:
- Local (sub)population sizes and growth rates influenced by birth, immigration, death, and emigration.

Metapopulations can created by habitat loss breaking up a once continuous range
Habitat loss can lead to the fragmentation of metapopulations.
- Example: Northern Spotted Owl affected by fragmentation of old-growth forests.
Effects of fragmentation include:
- Increased distance between patches, which decreases colonization rates (c).
- Decreased patch size and population density, which increases extinction rates (e).
- Net effect is to increase e/c ratio
- Metapopulation can go extinct even when patches of suitable habitat remain

Competition: An interaction where the fitness of one individual is reduced due to another competing for a shared resource.
- Resources is a limiting resource because it limits fitness (growth, reproduction, survival); if not, no competition occurs.
  - not all resources are limiting
  - if a resource is not limiting to a species, there cant be competition over it
- Intraspecific competition: Between individuals of the same species, affecting population density.
- Interspecific competition: Between individuals of different species.

Exploitation Competition: Indirect competition by depleting a shared resource (ex. they exploit the resource… teacher eating all donuts)
Interference Competition: Direct competition for access to a resource. (ex. prevent the other from accessing the resource, black vultures exclude turkey vulture from carcass feeding)
Apparent Competition: Unintentional effects due to third-party interactions, like predators.
- Example: the presence of one aphid species attracts a predatory beetle that causes a second aphid species to decline in number
What matters in competition is not how similar the competitors are, but shared resources

Competitive Exclusion: Two species cannot coexist indefinitely if they occupy the same niche; one will drive the other extinct or force niche partitioning.
Niche Partitioning: Different species adapt to exploit resources in unique ways to coexist.

Gause Experiments (1930s) on Paramecium species:
- P. aurelia drives P. caudatum extinct when grown together.
- P. caudatum suppresses P. bursaria but both can persist through niche partitioning (different resource use).
- Example of competitive exclusion

Competition influences species distributions based on resource availability.
- Example: Joe Connell studied barnacles in intertidal zones and found that Balanus outcompetes Chthalamus when both are present, revealing niche differences due to desiccation susceptibility.
- An example of interference competition

Niche: The set of resources used or occupied by an organisms
- includes space, time, season, food, microhabitat
Niche partitioning: no two species can occupy the exact same niche at the same time and space
- Seen in warblers that split foraging zones on trees to minimize competition
- Schoener’s Study (1974) on Anolis lizards:
  - Different sizes of lizards occupy slightly different perches or habitats, allowing coexistence despite overlapping resource use.
Fundamental Niche: The theoretically possible set of resources that CAN be occupied
Realized Niche: The actual set of resources occupied in practice.