Lesson 20

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Questions and Answers

What reproductive strategy involves an organism reproducing once and then dying?

r-selection

Iteroparity

K-selection

Semelparity (correct)

Which of the following is a characteristic of K-selected species?

Shorter gestation periods

Greater parental care (correct)

High number of offspring

Rapid maturation

What is a potential trade-off that organisms face when investing energy in reproduction?

Increased growth rates

Higher mating opportunities

Enhanced immune function

Reduced survival rates (correct)

Which organism is an example of a semelparous species?

Salmon Signup and view all the answers

What is the main reason male salmon have a lower survival rate compared to females after reproduction?

Suppressed immune system Signup and view all the answers

What is the primary focus of organisms that exhibit r-selection reproductive strategies?

Maximizing reproductive rates Signup and view all the answers

What might happen to Eurasian kestrels that rear more chicks each season?

Higher probability of death the following winter Signup and view all the answers

In which environment are K-selected species most likely to be found?

Stable and predictable Signup and view all the answers

Which of the following describes a density-independent factor affecting a population?

Clear-cutting of forests Signup and view all the answers

What is an effect of high population density on white-footed mice?

Delayed sexual maturation Signup and view all the answers

Intraspecific competition is best described as competition:

Within a species for limited resources Signup and view all the answers

Which scenario exemplifies interspecific competition?

Mountain lions and bobcats hunting for prey Signup and view all the answers

Which factor does NOT contribute to density-dependent regulation of population growth?

Clear-cutting of forests Signup and view all the answers

If a resource is abundant and not shared among organisms, what is the expected level of competition?

No competition Signup and view all the answers

What physiological changes occur in populations at high density?

Hormonal changes that delay reproduction Signup and view all the answers

Which of the following is a consequence of competition for a shared resource?

Reduced reproduction Signup and view all the answers

What is a characteristic of r-selected species?

They have a short generation time. Signup and view all the answers

Which of the following is a density-independent factor affecting population growth?

Floods. Signup and view all the answers

How do invasive species typically relate to r-selection?

They generally have short life spans. Signup and view all the answers

Which life history strategy is characterized by producing many, small offspring?

R-selection. Signup and view all the answers

In which environment would r-selected species most likely thrive?

Disturbed environments with abundant resources. Signup and view all the answers

What distinguishes K-selected species from r-selected species?

K-selected have a lower mortality rate. Signup and view all the answers

Which of the following is NOT a trait of r-selected species?

Long lifespan. Signup and view all the answers

What effect does population density have on density-dependent factors?

Effects vary based on population density. Signup and view all the answers

What happens to resource allocation when resources are abundant?

Extra resources are allocated to growth and reproduction. Signup and view all the answers

Which of the following is NOT considered a life history trait?

Habitat selection Signup and view all the answers

What defines semelparity in reproductive strategies?

Organism reproduces once before dying. Signup and view all the answers

How do life history traits evolve according to natural selection?

To maximize an organism’s fitness. Signup and view all the answers

When resources are scarce, how are they primarily allocated?

To basic maintenance with little for other processes. Signup and view all the answers

Which of the following factors does NOT typically influence age-specific survival rate?

Coloration of offspring. Signup and view all the answers

Which aspect of life history traits is most directly linked to reproductive success?

Frequency of reproduction. Signup and view all the answers

What is the primary purpose of the principle of allocation in resource management?

To maximize the survival and reproduction of organisms. Signup and view all the answers

Signup and view all the answers

Study Notes

Life History & Population Dynamics

Life history refers to the schedule of an organism's growth, development, reproduction, and survival. Traits evolve to maximize organism fitness.
Natural selection favors traits that increase an organism's survival and reproductive success.

Principle of Allocation

Organisms acquire a finite amount of resources.
Resources are allocated to life processes, including maintenance, growth, repair, acquiring resources, escaping predators, and reproduction.
Allocation impacts survival and fecundity. Resources allocated to one will come at the expense of the other.
Abundant resources allow for growth and reproduction.
Scarce resources prioritize basic maintenance.

Resource Allocation Trade-offs

Allocation of resources to different needs results in trade-offs.
Allocation to acquiring resources is prioritized over other tasks.
Maintaining needs must be prioritized over the other activities.
When resources are abundant, more resources can be allocated to reproduction.

Reproductive Strategies - Semelparity

Organisms reproduce only once before death. (Example: salmon)
Semelparity is adaptive when environments are unpredictable, and offspring survival is low.

Reproductive Strategies - Iteroparity

Organisms reproduce multiple times before death. (Example: humans)
Iteroparous organisms invest in fewer, larger offspring which often increases offspring survival rates.

Life History Trade-offs

Trade-offs between reproduction and survival are common.
Energy put into reproduction cannot be used to fuel growth or repair.
Reproductive decisions can impact an individual's winter survival.

Life History Strategies - K-Selection

Organisms in stable environments, near carrying capacity.
Examples: Bison, elephants, humans, whales, coconut palms
Characterized by: fewer offspring, longer gestation periods, and greater parental care.

Life History Strategies - r-Selection

Organisms in unstable or unpredictable environments, with low offspring survival.
Examples: Weeds, grasses, insects, rodents
Characterized by: many offspring, small body size, short time to maturity, short generation time, and little parental care
More r-selective organisms may have higher intrinsic growth rate (r).
Invasive species often have high r and perform well in disturbed environments.

Factors Regulating Population Growth - Density-Independent Factors

Factors that do not depend on population density, like floods, fires, drought, human development.
Seasonal cycles (wet/dry, cold/warm) are important density-indepedent factors.
Natural disasters like floods, drought, fire, and volcanic eruptions affect all sizes of populations.
Human effects/activities can influence population size, including clear-cutting, damming, and paving.

Factors Regulating Population Growth - Density-Dependent Factors

Factors whose impact depends on population density, such as competition, predation, herbivory, parasitism, disease, and waste accumulation.
Intraspecific competition occurs between members of the same species for limited resources.
Predation involves one species (predator) killing and consuming another species (prey). Predation increases as the density increases.
Herbivory is the interaction where an organism eats part of a plant.
Waste accumulation is a risk as population densities increase.

Density-Dependent Factors: Intrinsic Physiological Factors

At high densities, aggressive interactions increase and some organisms might not reproduce given limited resources and increased competition.

Density-Dependent factors: Competition

Limited resources may make competition intense.
Competition may cause decreased survival and reproduction.
Competition is less fierce if the resource is abundant or not shared.
Intraspecific competition occurs within a single species.
Interspecific competition occurs between different species.

Density-Dependent Factors: Waste Accumulation

High population density can lead to toxic waste accumulation which can endanger the population.
Waste accumulation can spread disease as concentrations increase

Density-Dependent Factors: Parasitism & Disease

Disease transmission rates increase in dense populations.
Parasites often facilitate disease transmission. High parasite density can cause high mortality.

Density-Dependent Factors: Predation & Herbivory

Predation rates increase as the density of predators or prey increases.
Herbivory impacts plants

Allee Effect

Individuals have more difficulty surviving or reproducing when population size is too small.

Living in Groups

Animals vary in the degree of sociality. Some are solitary, while others live in groups.
Benefits of group living include: increased foraging efficiency, increased awareness of predators, and defense against predators.
Costs of group living include exposure to parasites, wastes, greater predator detection risk, and more competition for resources.

Many Eyes Hypothesis & Flocking

Larger flock size can decrease time spent on vigilance.
Intermediate flock size yields optimal feeding time.

Many Eyes Hypothesis & Predator Confusion

Success in capturing prey is dependent on the flock size.

Age Structure of Populations

Age structure, plus sex, is important to understand population.
Different classifications of age structure can be used to categorize the overall population trends. This can be used to predict population growth/decline.

Survivorship Curves

Graphs showing how the number of individuals surviving changes over time.
Type 1 survivorship curves: Low mortality in early and middle years, high mortality in older individuals.
Type 2 survivorship curves: Constant mortality rates throughout the lifespan.
Type 3 survivorship curves: High mortality in early life, low mortality in older individuals.

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