Lesson 3 - Community Ecology

What makes up a realized niche?

• The result of species interactions

  • Competition

  • Predation

  • Parasitism

  • Mutualism

What is Competition?

• An interaction in which two species that depend on the same limited resource(s) each have a negative effect on the other

• Interspecific – between species

• Intraspecific – within a species

Exploitative Competition

• Indirect

• Refers to the indirect competition between individuals or species for limited
  resources within an environment.

• If one competitor uses a resource, it is not available for other competitors.

Interference Competition

• Direct

• Refers to direct interactions between individuals or species that impede the access of competitors to essential resources.

• Physical interference between individuals, usually for a resource.

Competitive Exclusion Principal

• States that if two species with identical niches compete, then one will inevitably drive the other to extinction.

• So how do competitors co- exist?

What three things can happen when competitors overlap?

1) Temporary co- existence (at reduced carrying capacity)

2) Competitive exclusion

3) Niche partitioning

Temporary Co-existence

• Both species continue to live in the area, but at lower numbers.

• But this tends to only last in the short term.

• i.e., temporary

Competitive Exclusion

• One of the species disappears from that area.

• Not usually random

• Some species are better competitors than others.

  • If two species’ niches perfectly overlap, the species that is better adapted to the niche will eventually outcompete the other.

• One species might arrive before the other.

  • Priority effects refer to the influence that the order and timing of species arrival have on a community

  • Competitors may inhibit other species from establishing

• Chance

  • Disturbance events may impact the abundance of one species more than the other

Niche Partitioning

• Both species continue to co-exist, but they diverge to occupy slightly different ecological niches within the shared habitat.

• i.e., a change in the realized niche

What are plants role in an ecosystem?

• Plants are mostly primary producers

• They provide the food that almost all of the other organisms present depend on

• Autotrophs

• Photosynthesis results in oxygen in aquatic environments and the atmosphere

• Carbon storage in plant tissues

• Also provide the physical structure of a community. In a forest, for example, root systems create a structure inhabited by mycorrhizal fungi

Foundation Species

• Shape their community!

• Provide an ecological foundation for many other species, even though they might not benefit from the interactions.

• e.g., physical foundation or infrastructure for a community or ecosystem

• Often highly abundant

• Examples

• Many trees, Corals, Kelp

Keystone Species

• A disproportionately large impact on its environment relative to its abundance or biomass

• Can be species in many types of ecological roles (Predators, Mutualists)

• Examples: (Wolves, Otters, Starfish)

Biomass

• The total mass of living organisms in a specific area

• Foundational Species (High Biomass + High Impact!)

• Keystone Species (Low Biomass + High Impact!)

Example of a Keystone Species (Starfish)

• When Pisaster was removed from the ecosystem

• The population of mussels dramatically increased and dominated space on the rocks

• Invertebrate community shifted from diverse assemblage of species to a dense mussel bed

• Reduced overall biodiversity

Interactions Within A Food Web

• Direct interactions occur between two species where one directly affects the other

  • Predation or mutualism

• Indirect interactions occur when the relationship between two species is mediated by one or more additional species

  • Trophic cascade → A change in a food web—usually caused by a change in an important predator—that causes changes in the abundance of other species in the web

Ecological Network

• A representation of the biotic interactions in an ecosystem, in which species are connected by interactions

• Organisms are interconnected via the various relationships within an ecological network

Food Webs

• A type of ecological network that shows who eats whom and how much

• Organisms mediate the movement of matter and energy through ecosystems

• Organisms sometimes eat more of certain resources and less of others

• Matter and energy can move through multiple pathways

• Are also a map for how pollutants and toxins flow through an ecosystem!

Multiple Choice Tips