Mutualism Costs and Benefits in Ecology

Mutualism Costs and Benefits

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

Mycorrhizae

• Mutualistic symbiosis between plants and fungi
• Exchange of sugars from plants for soil resources
• Two types:
  • Endomycorrhizae (arbuscular), penetrating plant cells
  • Ectomycorrhizae, forming a sheath around roots and penetrating between cells

Pollination

• Various insects collect pollen from gymnosperms (before angiosperms)
• Thrips (pre-angiosperms) have specialized structures for pollen gathering
• Flowers evolved in response to relationships with pollinators
• Flowers have structures to attract pollinators (anthers, filaments, nectar guides)

Frugivory

• Seed dispersal mechanism involving vertebrate animals and angiosperm plants
• Example: Black Cherry and birds (dispersal, frugivory)
• Seed excretion (excretion) aids germination by scarification

Reciprocal and Diffuse Selection

• Reciprocal selection: mutualism showing specificity between interacting populations
• Diffuse Selection: networks of interacting species where mutualists benefit from many interactions

Community Ecology

• Holistic View: treats communities as integrated organisms (with climax communities)
• Individualistic View: sees communities as collections of species whose presence depends on environmental factors

Species Richness

• Species richness varies geographically, increasing towards the equator
• Area larger at equator allows for more populations and ranges for speciation
• Tropical ecosystems have longer evolutionary histories, with more closely related species evolving faster

Species-Area Relationships

• Species richness increases with increasing survey area (area)
• Log-Log model for species-area relationship: Log S = Log C + z Log A

Assessing Species Richness - Species Surveys

• Rarefaction: technique to compare richness & assessing outcome of species surveys
• As more samples are taken, the number of species increase approaching/reaching an asymptote. Graph with x-axis = number of sites sampled and y-axis the average number of species encountered

Comparing Species Assemblages

• Ecological distance: Quantified difference between two entities based on set of variables
• MRPP (Multiple Response Permutation Procedure) groups sites based on similar species assemblages

Disturbance and Succession

• Disturbance affects species richness, impacting biomass accumulation
• High disturbance areas have less biomass, and low disturbance environments with high species richness.
• Succession: predictable series of changes after disturbance;
  • Establishment: early species establish changing conditions
  • Facilitation: early species benefits later species, creating more favorable conditions.
  • Inhibition: late-arriving species inhibit the establishment of earlier species.

Trophic Relationships

• Herbivores, predators, and bottom-up (autotrophs influencing heterotrophs, or top-down (predators influencing their prey) trophic relationships regulate communities.
• Succession changes species compositions in response to disturbance and resource availability in an area.

Stability and Richness

• Communities with more interactions (species) are generally more stable that those with more trophic interactions.
• Invasions: non-native species that, when introduced to an area, may quickly spread and replace native plant or animal communities potentially disrupting existing relationships.

This quiz explores the concepts of mutualism, focusing on costs and benefits for mutualists in ecological systems. From mycorrhizae to pollination and frugivory, understand how different organisms interact and benefit from these relationships. Test your knowledge on the intricate dynamics of these symbiotic partnerships.