BIOL4660_Lecture 7

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Aquatic Community Ecology

Fundamental Concepts
  • Community: A set of interacting species that co-occur in space and time.
  • Assemblage: Similar to a community; refers to co-occurring species.

Community Building Blocks

  • Functional groups: Assemblages of species performing similar activities or collaborating on ecological functions.
  • Guild: A set of species exploiting the same class of resources in a similar way.

Functional Species Groups

  • Additional layer of organization where:
    • Morphologically and/or ecologically similar species are grouped into taxonomic or functional groups.
    • Enables ecosystem-level modeling and assessments.
    • Example: Herbivorous plankton (cyclopoid copepods, calanoid copepods, cladocerans, rotifers).

Competition for Limited Resources

  • Major interactions include competition and predation.
  • Limited resources can include:
    • Food (for consumers)
    • Light (for primary producers)
    • Nutrients
    • Space
  • Competition types:
    • Intraspecific competition: between individuals of the same species.
    • Interspecific competition: between different species.
    • Competitive Exclusion: One species outcompetes another, leading to the latter's extinction.

Paradox of the Plankton

  • High variety of phytoplankton and zooplankton in seemingly uniform pelagic zones.
  • Possible reasons for non-competitive exclusion despite high diversity:
    • The environment is not homogeneous in time and space.
    • Species have unique tolerances/optima not reflected by taxonomy.
    • Competition may not be significant most of the time; resource availability could be more crucial.

Competition Avoidance Strategies

  • Environmental adaptations: Allow for reduced direct competition.
  • Habitat partitioning: Specialization in specific habitats to lessen competition.
    • Example: Different species of chydorid water fleas occupying unique lake areas.
  • Selective Feeding and Resource Partitioning:
    • Species may specialize on slightly different food resources to avoid overlap.

Predator-Prey Interactions

  • All consumers are considered predators, including herbivores termed as grazers.
  • Predatory activities can influence the population dynamics of prey, known as top-down control (e.g., zooplankton grazing impacts algal biomass).
  • Selective predation observed with species like the Alewife, which targets large-bodied zooplankton.

Lake Classification and Predation Dynamics

  • Differences in lake characteristics impact plankton food webs:
    • Temporary fishless ponds have high zooplankton diversity; permanent lakes often exhibit high planktivory.
    • Depth gradient influences predator evasion strategies; deeper lakes provide refuge against fish predation.

Defenses Against Predation

  • Behavioral Defenses:
    • Migrating to refugia, diel vertical migrations, swarming, escaping ("dead man's response").
  • Morphological Defenses:
    • Traits that impede predation, such as thick shells and long spines.
  • Cyclomorphosis: Seasonal morphological changes in response to predation.

Community Structure and Diversity

  • Reflects species diversity, composition, and size-spectrum within a lake.
  • Species Richness (S): The number of species in a community, impacted by lake type and size.
    • Higher richness seen in larger lakes or those close to other lakes.
    • Shannon Diversity Index is a valuable metric for assessing community diversity.
  • Lake productivity is also crucial:
    • Mesotrophic lakes exhibit the highest diversity compared to hypereutrophic or ultraoligotrophic lakes.

Fish and Zooplankton Diversity

  • Fish Species Richness (S) increases with drainage basin and lake area; older lakes generally exhibit more species.
  • Zooplankton Species Richness (S) also shows correlation with lake size, with temperature and predation affecting richness.

Phytoplankton Diversity

  • Only weak evidence linking phytoplankton species richness to lake area, indicating spatial scaling effects.

Key Takeaways

  • Understand the interplay between species in communities, the role of competition vs. predation, and the implications on biodiversity and ecosystem functioning.