Chapter 15 (Mutualism)

Mutualisms and Strong Interactions

  • Definition of Mutualisms:

    • Interactions between two species that benefit both species.

    • Examples include:

    • Dispersal

    • Pollination

    • Nutrition

    • Protection (Janzen 1985)

Types of Ecological Interactions (Adapted from Smith 1996)

  • Table 13.1 - Types of Species Interactions Defined by Net Impact:

    • Competition:

    • Effect on Species 1: -

    • Effect on Species 2: -

    • Example: A lion and a hyena fighting over a carcass; both expend energy and risk injury.

    • Mutualism:

    • Effect on Species 1: +

    • Effect on Species 2: +

    • Example: A penstemon and the bee that pollinates it; the penstemon spreads genes and the bee gets food.

    • Predation/Parasitism:

    • Effect on Species 1: +

    • Effect on Species 2: -

    • Example: A fungus grows on a wild rosebush; fungus gains energy as the rose experiences illness.

    • Commensalism:

    • Effect on Species 1: +

    • Effect on Species 2: 0

    • Example: An orchid growing on a tree; the orchid benefits without harming the tree.

    • Amensalism:

    • Effect on Species 1: 0

    • Effect on Species 2: -

    • Example: A sunflower struggles to grow in the shade of a walnut tree, negatively impacting the sunflower but not the tree.

    • Neutralism:

    • Effect on Species 1: 0

    • Effect on Species 2: 0

    • Example: Two species of insects live on the same plant but have no effect on each other due to niche differentiation.

Resource/Dispersal Exchange in Mutualistic Relationships

  • Plants and Pollinators/Seed Dispersers:

    • Various bees illustrated pollinating different types of plants, e.g., blue orchard bees, leafcutter bees, etc.

Defense/Resource Exchange Mutualisms

  • Pistol Shrimp and Coral Interaction:

    • Findings: Corals occupied by pistol shrimp and crabs are attacked less frequently compared to corals without these crustaceans.

    • Graph Data:

    • Predation rate (%) on coral species with vs. without crustaceans.

  • Acacia and Ants Mutualism:

    • Findings: Survival of acacia suckers is much higher where occupied by ants.

    • Graph Data:

    • Survival percentage tallied over various dates comparing conditions with and without ants.

  • Coral and Zooxanthellae Interaction:

    • Observations: Corals without zooxanthellae excrete ammonium, while corals with zooxanthellae absorb it from the environment.

    • Graph Data: Ammonium concentration plotted over time.

Mycorrhizal Fungi Resource Exchange

  • Fungal Interaction with Plants:

    • Findings:

    • Under low nutrient conditions, plants allocate more energy to roots and mycorrhizal fungi.

    • Conversely, under high nutrient conditions, they allocate less.

    • Graph Data: Shoot biomass vs root biomass under different nutrient conditions.

Evolution of Mutualisms

  • Key Questions on Mutualism Evolution:

    • How do mutualisms evolve?

    • Why does the strength of mutualistic relationships vary?

    • Can mutualistic relationships break down?

    • Is the evolution of mutualisms different from that of other strong interactions?

  • Types of Mutualism:

    • Obligate Mutualism: Individuals cannot survive without the mutualism.

    • Facultative Mutualism: Individuals can survive independently of the mutualism.

Strategies and Selection in Mutualisms

  • Types of Mutualists:

    • Successful mutualists that give and receive benefits.

    • Unsuccessful mutualists that give benefits but receive none.

    • Non-mutualists that neither give nor receive benefits.

  • Fitness Relationships:

    • Fitness of successful mutualists > Fitness of non-mutualists

    • Fitness of successful + unsuccessful mutualists > Fitness of non-mutualists

Breakdown of Mutualism

  • Environmental Influence:

    • Strong selection for mutualism may not occur under certain environmental conditions, such as in fertilized soil patches.

    • Natural selection for mutualism might occur on a larger scale across various patch types (fertile and infertile).

  • Example of Breakdown:

    • Visual representation of Angraecum sesquipedale var. angustifolium and its hawk moth pollinator illustrates potential mutualism breakdown.

Herbivorous Insect Interactions with Acacia

  • Impact of Ants on Herbivory:

    • Acacia shoots without the presence of ants have significantly higher numbers of herbivorous insects compared to those with ants.

Overall Impact of Mutualisms

  • Ecological Implications of Mutualisms:

    • A recent study demonstrated that an invasive plant-fungal mutualism can drastically reduce arthropod diversity, highlighting the extensive effects mutualisms have on community structure and food webs.

    • Research Findings:

      • Reduction of arthropod abundance by 70% and diversity by nearly 20%.

      • Herbivorous species affected more than carnivores.

Additional Research and Insights

  • Studies Reflecting Mutualism and Disease:

    • Increased exploration of knowledge regarding how gut microbes and parasites affect immunity could lead to innovative treatments for various immunological disorders.

  • Parasite Impacts:

    • Parasites influence host health and behavior, often possessing capacities that may inadvertently benefit hosts through immunological responses balance.

Summary of Key Terms and Definitions

  • Parasites: Organisms that live on tissues of their host, reducing host fitness without typically killing them.

  • Parasitoid: An insect whose larva consumes its host and leads to its death.