Life cycles animals lecture 6

Question 1

What are the two primary models of population growth?

Answer 1

The exponential growth curve and the logistic growth curve.

Question 2

What does the exponential growth curve assume?

Answer 2

It assumes unlimited resources and no environmental constraints, leading to rapid, unchecked population growth.

Question 3

What does the logistic growth curve consider?

Answer 3

It considers the carrying capacity of the environment, which is the maximum population size that the environment can sustain. As the population approaches this carrying capacity, the growth rate slows down due to resource limitations and increased competition.

Question 4

How does individual fitness change with increasing population density?

Answer 4

Individual fitness tends to decrease due to increased competition for resources, resulting in a decrease in the per capita growth rate.

Question 5

What is compensation in the context of population density?

Answer 5

Compensation refers to higher growth rates at low population densities.

Question 6

What is the Allee effect?

Answer 6

The Allee effect occurs when individual fitness decreases at low population densities, leading to a decrease in the per capita growth rate.

Question 7

What is depensation?

Answer 7

Depensation is the specific decrease in the per capita growth rate at low population densities, associated with the Allee effect.

Question 8

Under what conditions is the Allee effect expected to occur?

Answer 8

The Allee effect is expected to occur when
- low population densities negatively impact individual fitness and reproduction
- such as in the absence of
1. reproductive aggregation
2. cooperative defense
3. predator satiation
4. cooperative feeding

Question 9

How does lack of reproductive aggregation affect species?

Answer 9

It hinders mate finding and results in lower fertilization rates at low population densities.

Question 10

Why is cooperative defense less effective at low densities?

Answer 10

Because species that rely on group behaviors for defense against predators cannot form effective groups at low densities.

Question 11

What is predator satiation, and how is it related to population density?

Answer 11

• Predator satiation occurs when prey aggregations overwhelm predators, reducing individual predation risk.
• Without sufficient aggregation at low densities, individuals are more vulnerable to predation.

Question 12

How does cooperative feeding influence species at low densities?

Answer 12

Species that rely on cooperative feeding behaviors may struggle to exploit food resources efficiently at low densities.

Question 13

How does gamete dispersal affect species with the Allee effect?

Answer 13

In species where fertilization depends on the proximity of mates, low population densities can result in reduced fertilization rates due to poor gamete dispersal.

Question 14

Why is synchronicity in reproduction important?

Answer 14

The age of gametes and the timing of reproduction can affect fertilization rates. Low densities can disrupt this synchronicity.

Question 15

How do sea urchins demonstrate the Allee effect?

Answer 15

• Sea urchins tend to aggregate, ensuring better fertilization rates.
• When densities fall below 0.5 individuals per square meter, the relationship between larval production and density becomes non-linear, leading to low larval production.

Question 16

What happened to the conch population in the Bahamas in relation to the Allee effect?

Answer 16

When conch densities fell below 48 individuals per hectare, no mating occurred, demonstrating the Allee effect.

Question 17

How does sperm concentration affect fertilization rates in abalones?

Answer 17

• Below a certain sperm concentration threshold, fertilization rates are nearly zero
• but they increase with higher sperm concentrations.
• However, very high sperm concentrations can lead to polyspermy and abnormal embryos.
• there is an optimum (not too high, not too low)

Question 18

How have Atlantic cod populations shown the Allee effect?

Answer 18

• Atlantic cod populations have declined significantly, relying on external fertilization and spawning aggregations.
• Low densities and reduced sperm concentrations result in lower fertilization rates, contributing to the lack of population recovery.

Question 19

How does predation risk vary with population density?

Answer 19

Predation risk is higher at low densities but potentially reduced at higher densities due to group defenses.

Question 20

What is the cultivation effect in trophic relationships?

Answer 20

• The cultivation effect occurs when a decline in predator populations leads to an increase in prey populations, which then eat the juveniles or larvae of the predator, further complicating predator recovery.
• shown in example of cod

Question 21

How does the cultivation effect apply to Atlantic cod?

Answer 21

The cod preys on herrings and capelins, which in turn prey on cod larvae. This interaction can hinder cod population recovery.

Question 22

How is the Allee effect quantified?

Answer 22

• The Allee effect can be quantified using the value of δ, which describes the relationship between density and recruitment/reproduction
• A δ value greater than 1 indicates a significant Allee effect.

Question 23

What does a recruits per Spawning Stock Biomass (SSB) ratio less than 1 at low densities indicate?

Answer 23

It indicates the presence of the Allee effect

Question 24

Why is understanding the Allee effect important for conservation?

Answer 24

Understanding and addressing the Allee effect is crucial for the conservation and management of species, particularly those with declining populations or at risk of extinction.

Question 25

How do current velocities affect fertilization rates?

Answer 25

Higher current velocities tend to decrease fertilization rates.

Question 26

How do aggregative distributions of sea urchins at low densities influence fertilization rates?

Answer 26

Aggregative distributions at low densities ensure better fertilization rates, even with a small number of individuals. When densities fall below 0.5 individuals per square meter, larval production and density become non-linear, leading to low larval production.