Ricklefs Chapter14

Chapter 14- Species Interaction

Consumer Resource Interaction: predator-prey, herbivore-plant, and parasite-host relationships
these interactions are the basis for two additional types of interactions: competition and mutualism
Competition: when two consumers share the same resource, each reduces the availability of the resource to the other
Mutualism: interactions between two species that benefit both
When we consider that a species can benefit from an interaction (+), suffer (-), or be unaffected (0), the possible combination of effects are:
+/-, -/-, +/+, +/0, or -/0 (0/0 represents the absence of any consequential interaction
Symbiosis**: “living together” individuals of different species that live in close association

All Consumers are Involved in Consumer-Resource Interactions**

Consumers: predator, parasite, parasitoid, herbivore, and detritivore
Predators: capture individuals and consume them, thereby removing them from the prey population and gaining nutrition to support their own reproduction
Parasite: consumes parts of a living prey organism, or host
Parasitoid: species of wasps and flies whose larvae consumes the tissues of living hosts/ resemble parasites
Herbivores: eat whole plants or parts of plants
grazing: consumption of a portion of a plant’s tissues
browsing: when applied to woody vegetation
Detritivores: consume dead organic material- such as leaf litter, feces and carcasses

The Dynamics of Consumer-Resource Interactions Reflect Mutual Evolutionary Responses
- Resource organisms have as many tactics to avoid being eaten as their consumers have to hunt them
- Avoiding predators may result in reduced growth rates

Parasites Maintain a Delicate Consumer-Resource Relationship with their Hosts
- Parasites are usually much smaller than their hosts and live either on their body surfaces or inside their bodies
- The effects of parasites on host fitness varies dramatically: could hurt or benefit
- Parasites that live inside, or in close association with, a larger organism enjoys a benign physical environment regulated by their host
Life Cycles of Parasites - pg 293 (Ricklefs)
- Host organisms have a variety of mechanisms to recognize invaders and destroy them
Virulence: a measure of the capacity of a parasite to invade host tissues and proliferate in them. The balance between parasite and host populations is influenced by the virulence of the parasite and by the immune response of the host

Herbivory Varies with the Quality of Plants as Resources
- Plant defenses against herbivores include the inherently low nutritional value of most plant tissues as well as toxic compounds that plants produce and sequester for their defense
- The nutritional quality and digestibility of plants is critical to herbivores
Tannins: oaks and other plants sequester compounds called tannins in vacuoles in their leaves, which bind to plant proteins and inhibit their digestion—-can slow the growth of some organisms
Secondary Compound: a compound used by plants not for metabolism, but for other purposes, chiefly defense (tannins)
Constitutive Defenses: types of defensive chemicals are maintained at high levels in plant tissues at all times
Induced Defenses: activated by herbivore damage
- Inducibility suggests that some chemical defenses are too costly to maintain when herbivory is light or absent

Competition May be an Indirect Result of Other Types of Interactions
Trophic Cascades: indirect actions (ie: predator (+) > herbivore (-) > plant (+) are felt across multiple trophic levels
- Interactions between species are not rigid, indeed it is common for these interactions to change over the life cycle

Individuals of Different Species Can Collaborate in Mutualistic Interactions
- Many interactions between species benefit both participants (mutualisms)
Trophic Mutualisms: usually specialized in complementary ways to obtain energy and nutrients
Defensive Mutualisms: receive food or shelter from their partners in return for defending those partners against their consumers
- Ecological systems create their own dynamic properties that cannot be inferred from the individual components of the system, but rather depend on the ways in which species interact

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