L7: Species Interactions: Competition and Exploitation

Define competition

reduction in fitness due to shared use of a resource in limited supply

What are the two general types of competition?

◦ Intraspecific competition
 between individuals of same species
◦ Interspecific competition
 between individuals of different species

Why is intraspecific competition so difficult to study?

Plants:
◦ easier to confirm

Animals:
◦ difficult to confirm due to mobility & behavior

What is the self-thinning rule? Why does it show this pattern?

A reduction in population density as a stand of plants increases in biomass. This pattern occurs because as plants grow larger, they require more resources, leading to increased competition and the death of smaller individuals.

What are the two types of interspecific competition? What are the challenges for studying each one?

• Exploitative competition:
  ◦ individuals compete indirectly through their
  mutual effects on availability of a shared, limiting
  resource
   e.g. diatoms competing for silica; plants depleting
  water

• Interference competition:
  ◦ individuals compete directly for access to a
  shared, limiting resource
   antagonistic (aggressive) actions
  interfere with
  competitor’s ability to use resource

Explain the competitive exclusion principle. How may competition influence niches?

where one species out competes each other but they both negatively affect each other

What is the difference between exploitative competition and interference competition?

exploitative competition:
◦ individuals compete indirectly through their
mutual effects on availability of a shared, limiting
resource

interference competition:
◦ individuals compete directly for access to a
shared, limiting resource

What is the difference between competitive exclusion and competitive coexistence?

Competitive exclusion occurs when one species outcompetes another for resources, but still negatively affects each other. Competitive coexistence allows multiple species to share the same resources without displacing each other.

What is the Lotka-Volterra competition model? What can it be used for? What form of population growth is utilized in the model?

Lotka–Volterra competition model: expands logistic
growth model to incorporate interspecific competition between two species. It can be used to predict the outcome of competition.

What is character displacement? How is it associated with competition and evolution? Why is it so difficult to demonstrate?

the evolution of divergent phenotypes between competing species that results in resource partitioning.

Character displacement difficult to demonstrate:
◦ requires lots of evidence
◦ differences must have genetic basis
◦ differences must have evolved in place
◦ demonstration of competition of certain resource

How may amensalism, exploitation, competition, mutualism, and commensalism associate with each other in species interactions?

These are various forms of species interactions that can affect population dynamics and community structure. Each interaction type can influence resource availability, reproductive success, and survival rates among species in an ecosystem.

What are the three forms of exploitation? How do they compare with each other?

(-/+)

1. Predation: kill and consume pray

2. Herbivory: Consume living plants tissues/fluids

3. Parasitism: live on or in a host, consumes tissue/fluids

Define mutualism.

(+/+)

interaction where both species benefit from the relationship, enhancing each other's survival and reproduction.

What is the difference between facultative mutualism and obligate mutualism?

1. facultative mutualism: each species can live without the other

2. obligate mutualism: neither species can exist without the other

Why form mutualisms? What could be potential advantages and disadvantages to forming mutualisms?

1. Why form mutualisms?
   ◦ protection
   ◦ nutrients requirements/limitations
   ◦ habitat requirements
   ◦ reproduction – pollination requirements
   ◦ dispersal requirements

2. Key factor: relative costs & benefits
   ◦ benefits exceed costs mutualism

Know and be able to explain the advantages and disadvantages of the defensive adaptations for animals in response to exploitative pressures. What could be potential counter-adaptations?

1. Animals:
   • physical defenses:
   ▪ large size
   ▪ speed and agility
   ▪ body armor

   • physical defenses
   • chemical defenses
   • aposematism (warning coloration)

   • crypsis (camouflage)

   • mimicry

   • behaviors

counter-adaptations
1. visual or chemical camouflage to sneak up on prey

2. tolerance or detoxification of chemical defenses

Know and be able to explain the advantages and disadvantages of the defensive adaptations for plants in response to exploitative pressures. What could be potential counter-adaptations?

1. Plants:
   • physical defenses:
   ▪ tough leaves
   ▪ spines, thorns, trichomes
   ▪ mimicry
   ▪ movement (leaf folding/dropping)

   • secondary plant compounds (toxins/chemicals)

   • compensation (removal of plant parts to produce new growth)

counter-adaptations
1. visual or chemical camouflage to sneak up on prey

2. tolerance or detoxification of chemical defenses

Why are exploitative interactions so complex and difficult to study? What effects can these have on communities?

Exploitation relationships are complex & dynamic
◦ temporally & spatially
◦ population cycles (reciprocal oscillations)

Depends on:
◦ prey/host life history
◦ food supply requirements/limitations
◦ predators/parasites role

What is the Lotka-Volterra predator-prey model? Why does it result in oscillations?

A mathematical model that represents the interactions between predator and prey populations, demonstrating cyclical oscillations in their populations.

How may food supply, prey, and predators influence predator-prey oscillations? Be familiar with the snowshoe hare and lynx example.

Food supply and the availability of prey influence predator-prey dynamics, leading to cyclical population changes, as seen in the interactions between snowshoe hares and lynxes.