Mutualism Costs and Benefits

Mutualism Costs and Benefits

• Fitness for non-mutualist (Fm) = 0
• Fitness for successful mutualist (Fsm) = Benefit - Cost
• Fitness for unsuccessful mutualist (Fum) = -Cost
• p(Fsm): frequency of successful mutualists
• q(Fum): frequency of unsuccessful mutualists
• p(Fsm) + q(Fum): value of benefit relative to cost
• p(Fsm) + q(Fum) > 0

Mycorrhizae

• Mutualistic symbiosis between plants and fungi
• Exchange sugars from the plant for soil resources
• Two types:
  • Endomycorrhizae (arbuscular): penetrates plant cells
  • Ectomycorrhizae: sheath around root, hyphae penetrate between cells

Pollination

• Life History: Insects collected pollen from gymnosperms, before angiosperms
• Thrip species: specialized structures for pollination for pre-angiosperms
• Relationship between thrips and pre-angiosperms
• Flowers: specialized for attracting pollinators
  • Anthers positioned on filaments
  • Nectar guides direct insects to nutrients

Frugivory

• Seed dispersal mutualism between vertebrates and angiosperms
• Fruit develops from the ovary of a fertilized flower
• Examples include Black Cherry and birds (dispersal mechanism robins and jays)

Reciprocal Selection

• Mutualism that develops specificity in populations.
• Relationships exclusive to a pair of populations
• Seen in pollinator mutualisms for advantages in getting pollen to correct species

Diffuse Selection

• Network of species that interact mutually
• Mutualists benefit from interaction with more than one species.
• Example: Frugivory between Black Cherry and birds (seed needs place to live)

Complexity of Communities

• Holistic View (Clements): Communities as organisms
  • Clements' Plant Succession (unit of vegetation and climax formation)
• Individualistic View (Gleason): Individualistic concept of plant association
  • Local environment determines where a plant lives
  • Variability in environment and vegetation varying in time and space

Species Richness and Assemblage

• Richness varies geographically, increasing towards the equator
• Geographic area allows for larger ranges and allopatric speciation
• Evolutionary time is longer in tropical ecosystems
• Tropical populations have shorter generation times for faster evolution
• Richness increases predictably with area surveyed
• Log-log model: [LogS = LogC + z • LogA]
  • Y-axis: LogS = log of species
  • X-axis: LogA = log of areas
  • Intercept: C; Slope: Z
• Rarefaction: technique to compare patterns of richness and assessing outcomes of species surveys

Comparing Species Assemblies

• Ecological distance: quantified difference between entities based on variables.
• Entities = sites, variables = species, distance = the number of variables sites differ in
• Matrix (within group and between group distances); tested via Mantel test
  • Correlation tested between matrices. Similar patterns indicate correlated
• Example: Restored Watershed, Pre-existing Wetlands studied for frog species and habitat

Ecological Succession and Disturbance

• Disturbance: fundamental force of change, communities are defined through disturbance in an expected state
• Structure or function disruption causes change from partial to total loss or biomass change due to herbivores, pathogens, man or environmental factors like wind
  • High disturbance: Low biomass accumulation or removal.
  • Low disturbance: high biomass accumulation or control by strong competitors
• Succession : predictable changes within a community after disturbance (e.g.,fire adapted communities)
  • Establishment of new seedlings/species after disturbance.
  • Facilitation, inhibition: early species help out, later ones compete better). These changes cause a change in conditions creating opportunities for later species.

Trophic Relationships

• Herbivores can provide disturbance and limit plant community succession.
• Predators consume herbivores allowing the community below to flourish.
• Bottom up, assemblage : autotrophs (plants) influence the assemblage of heterotrophs (consumers), succession in response to abundance, Examples: White-eyed vireo habitat variability, changes in response. Top down: predators regulate species assemblage
  • Examples: sea otters regulate kelp forest by eating sea urchins, blue crabs and salt marshes due to crabs eating snails.

Island Biogeography and Invasion/Resilience

• Species richness on islands is related to island area and distance.
• More species will persist on larger islands closer to the mainland, because there will be greater immigration rates.
• If populations of an island were disturbed, species richness should remain the same through time while assemblages (relative proportions of different species) change in response to immigration and extinction.