Ecological Relationships and Interactions

ECOLOGICAL RELATIONSHIPS

• Types of Ecological Interactions:

  • Predation: (+/-) One species benefits (predator), the other is harmed (prey).

  • Parasitism: (-/+) One organism (parasite) benefits at the expense of another (host).

  • Mutualism: (+/+) Both species benefit from the relationship.

  • Commensalism: (+/~) One species benefits, the other is neither helped nor harmed.

COEVOLUTION:

• Predator-Prey Dynamics:

  • Arms Race: Evolutionary changes occur in predator and prey; e.g., bats and moths have been in a 55 million year coevolutionary struggle.

PREDATORS & PREY

• Examples of Predator Adaptations:

  • Hammerhead Shark: Eyes on the edges provide panoramic vision and agility for hunting.

  • Star-nosed Mole: Lives underground, uses its unique nose to navigate textures without eyesight.

  • Great Grey Owl: Specialized facial structure enhances sound localization for hunting.

EFFECTS OF PREDATORS ON PREY ABUNDANCE

• Population Studies:

  • Dingo removal in Australia resulted in red kangaroo populations increasing 10-30x.

  • Removing skunks led to higher duck hatchling survival in North Dakota.

  • Experiments show predators significantly influence prey populations.

PREDATOR-PREY CYCLES

• Charles Elton's Research (1845-1935):

  • Studied lynx and hare pelts to outline predator-prey cycles lasting approximately 10 years.

  • Analysis initiated a deeper study into the ecological forces driving these cycles.

FOOD WEBS IN THE BOREAL FOREST

• Interconnectivity:

  • Key organisms affecting lynx population: various birds of prey, small mammals, herbivores.

  • Removing lynx or hares would disrupt the entire food web, demonstrating their ecological significance.

MULTILEVEL CONTROL OF HARE ABUNDANCE

• Research Findings:

  • Studies indicate hare abundance is influenced both by top-down control (predators) and bottom-up control (food availability).

  • Long term experiments revealed complex interactions in populations of hares and the ecological ramifications.

PARASITISM

• Definition:

  • Parasitism involves one organism living on or in a host, inflicting harm adapted through structural modifications.

• Ecological Impact:

  • Influences host behavior, distribution, and community species diversity.

EFFECTS OF PARASITES ON BEHAVIOR

• Examples:

  • Trematodes manipulate periwinkles to increase visibility to predators.

  • Flatworms cause amphipods to swim closer to the surface, increasing predation risk.

PARASITE INFLUENCE ON HUMAN BEHAVIOR

• Study Findings:

  • Students with T. gondii exposure more likely to major in business-related fields, hinting at personality shifts due to parasitic infections.

HOST ABUNDANCE AND PARASITES

• Impact on Populations:

  • Ticks increase mortality in nestlings, demonstrating the parasite's effect on host population dynamics.

  • Red fox populations plummet due to mange, causing rapid hare population increases due to reduced predation.

MUTUALISM

• Definitions:

  • Obligate Mutualism: Species are dependent on each other for survival.

  • Facultative Mutualism: Species benefit from each other but can thrive independently.

TROPICAL BENEFITS OF MUTUALISM

• Benefits:

  • Trophic: Sharing resources such as energy and nutrients.

  • Defensive: Protection against threats like predators and parasites.

  • Dispersive: Assistance with reproduction, e.g., pollen and seed transportation.

COMMENSALISM

• Definition:

  • An interaction where one species benefits while the other is unaffected.