BIO 192 Exam III

Inclusive fitness

producing your own offspring and helping close relatives with offspring

What is population ecology

the study of factors affecting the size of a population and how it changes over time

What is a population?

Group of individuals of a single species living in the same general area

Population size is impacted by… (4 things)

• Birth

• Death

• Immigration

• Emigration

Often, we model immigration and emigration as very _______ in a population

low

Population size can vary depending on _________

taxa

where they…

• reach a stable zie

• fluctuate irregularly

• rise and fall in regular cycles

What is taxa?

groups of organisms classified based on shared characteristics

Species example of population graph that reaches a stable size over time (stable)

Bacteria

• rapid population growth

• persist at high numbers

• around carrying capacity

Species example of population graph that fluctuates irregularly (irregular)

Algae

• Boom-busted based on external factors

• Influx of phosphorous

Species example of population graph that rises and falls in regular cycles (cyclic)

Hare

• Cyclical with predator

• predator-prey

• boom and bust

What are the four population size graphs

Stable, Irruptive, Cyclic, Irregular

Species example of population graph that exhibits very little change in population size over time punctuated with a boom-bust (irruptive)

Deer

When birth rates = death rates, there is ______ population growth

stable

This population graph is difficult to predict and depends on abiotic and biotic factors

irregular

This population graph shows a predictable boom-bust and exhibits a predator-prey cycle of rise and fall

cyclic

What is population density

Number of individuals per unit area or volume
EX) number of oak trees per square kilometer in Illinois

What are density-dependent factors?

• Change in birth rate or death rate that does fluctuate with population density

• Implies certain limiting factors cause growth rate to change as density increases
  EX) Competition for limited food among members of a population

What are density-independent factors?

• Change in birth rate or death rate that does not fluctuate with population density

• Cannot regulate population size
  EX) Natural disasters like forest fires – impacts small or large pops equally

Population density is __________

variable

Kelp-Perch population density

Density dependent

Kelp abundance is the limiting factor

Low density in Kelp-Perch population density means…

• More hiding spots

• Low death rate

• Lower predation

High density in Kelp-Perch population density means…

• Fewer hiding spots

• High death rate

• Greater predation

Population density is impacted by…

• Competition for resources

• Territoriality

• Toxic wastes

• Disease

• Intrinsic factors

Mechanisms that cause density-dependent regulation:

• Predation

• Disease

• Competition for resources

• Intrinsic physiological factors

• Territoriality

• Toxic wastes

Impact on population density from competition for resources

• High population density

• Intense competition for resources

• Reduction in birth rates

EX) Agriculture

Farmers reduce competition by applying fertilizers to reduce nutrient limitations on crop yield

Impact on population density from disease

• High population density

• Transmission rate increases as the population becomes more crowded

• Increase in death rates

EX) Virus/bacterial infection like influenza, COVID, and tuberculosis affect a greater percentage of people in densely populated cities than in rural areas

Impact on population density from territoriality

• High population density

• Spaces become the resource for which individuals compete

• Decrease in birth rates

• Increase in death birth

EX) Marking. Cheetahs use chemical markers in urine to warn other cheetahs of their territorial boundaries

Impact on population density from intrinsic factors

• High population density

• Physiological factors regulate populate size

• Birth rates change based on effect

• Death rates change based on effect

EX) Hormones. Hormonal changes in white-footed mice delay sexual maturation and depress the immune system at high density. Birth rates drop even when food and shelter are abundant

Impact on population density from toxic wastes

• High population density

• Accumulation of toxic wastes at high population

• Birth rates change based on toxic concentration

• Death rates change based on toxic concentration

EX) Ethanol. Concentration of ethanol produced by brewer’s yeast becomes toxic at high population density

Are large mammal population stable?

Long-term studies show that they can fluctuate substantially

EX) Isle Royale mammals, which inhabit Isle Royale, a 200 sq mile island in Lake Superior

• Two major population increases and collapses in the moose population in the last 50 years

• The first collapse coincided with a peak in the wolf population (density dependent), the second with harsh winter conditions (density independent)

Predictable cycles in population size (Snowshoe hare and Lynx example)

Some populations undergo regular boom-and-bust cycles

EX) snowshoe hares and lynx both follow roughly 10-year population cycles in the forests of northern Canada and Alaska

Expect Lynx to increase and decrease in response to the availability of prey. Unclear why the hare population cycles.

Two hypotheses proposed to explain the
hare’s population cycle.

• 1. It follows a cycle of winter food supply (less food in winter for hares)

  • Hypothesis 1 – Winter food supply
    Cycles should stop if the food supply is increased. Those populations provided with additional food increased in size.
    But continued to cycle

  • Food supplies alone do not cause the
    population cycle in snowshoe hares

• 2. It is caused by predator-prey
  interactions (lynx numbers directly impact hare numbers)

  • Hypothesis 2 – Predator-prey
    Predation by several species killed 95% of the hares in these studies
    -None died of starvation

  • When predators were excluded from
    certain areas, the collapse in hare
    survival was nearly eliminated.

  • Overexploitation by predators is an
    essential factor affecting snowshoe hare
    cycles

Population size can vary depending on taxa (Rabbits from Australia example)

• Invasive species biology may provide clues

• No natural predators, population explodes in local area

• Food resources (i.e., grass) then become scarce and population density drops

• Human-induced population controls
  - Still results in cyclical patterns

What is dispersion?

Pattern of spacing among individuals within the boundaries of the population

Name the three types of dispersion patterns

Clumped, Uniform, and Random

How are dispersion patterns determined?

• Determined by the spacing among individuals within the boundaries of a population

• Differences in spacing can provide insight into the biotic and abiotic factors affecting individuals

Describe the Clumped Dispersion Pattern

• Most common pattern of dispersion

• Individuals aggregate in patches

  • Individuals may aggregate in areas of
    high resource availability or favorable
    physical conditions
    -Resources are patchy

  • Mating behavior and group predation
    or defense against predators can also
    influence clumped dispersions

Why might individuals aggregate in certain areas in patches? (clumped dispersion pattern)

To be in areas of high resource availability or favorable physical conditions

Since ____________ are patchy, so will be population dispersion (clumped pattern)

resources

Beyond resource dispersion and physical conditions, why might indiviudals clump in one area?

Mating behavior and group predation or defense against predators

Describe the Uniform Dispersion Pattern

Individuals are evenly spaced

Why might individuals exhibit a uniform dispersion pattern?

Direct interactions between individuals

• Some plants secrete chemicals that inhibit germination and growth of competing individuals

• Animals often exhibit territoriality, the defense of a bounded physical space against other individuals

What do some plants do that trigger a uniform dispersion pattern?

Some plants secrete chemicals that inhibit germination and growth of competing individuals

_________ often causes a uniform dispersion pattern

Territoriality

Describe the Random Dispersion Pattern

• Unpredictable spacing among individuals

• Position of each individual is independent of other individuals

• Typically impacted by abiotic factors

Random dispersion patterns are often impacted by _______ factors

Abiotic (soil, pH, precipitation, salinity)

In random dispersion patterns, there is ______ variation in spacing among organisms

high

Random dispersion patterns commonly occur within _________ environment

uniform

Wind dispersed plants is an example of _______ dispersion

random

What is a survivorship curve?

Plot of the proportion or numbers in a cohort still alive at each age.
Illustrates pattern of survivorship in a population

Humans usually exhibit type ___ survivorship curves

type 1.

Survivorship drops steeply at old age

Describe type 1 survivorship curves

• Low death rates in early/middle life

• Survivorship drops steeply at old age

• Few offspring

• High parental investment

Which survivorship curve often shows high parental investment?

Type 1

Which survivorship curve often shows few offspring?

Type 1

Many large mammals, including humans and elephants, exhibit what type of survivorship curve

type 1

Describe a type II survivorship curve

Constant mortality throughout life

What types of animals exhibit a type II survivorship curve?

• Rodents

• Lizards

• Invertebrates

• Annual plants

Which survivorship curve type is linear?

Type 2

Describe a type III survivorship curve

• High death rate early in life

  • Low survivorship

• Low death rate in late life

• High number of offspring

• Low parental investment

Opposite to type I survivorship curves, type _____ curves exhibit low death rate in late life and low parental investment

type III

What are some organisms that have a type III survivorship curve?

• Oysters

• Octopus

Population size is impacted by…

• Birth

• Death

• Immigration

• Emigration

Often, we model _______ and _______ as very low in a population

immigration and emigration

Maximizing reproductive success

Understanding life history involved learning about how organisms survive to reach reproductive age and then characterizes differences in their reproductive strategies

An organism’s life history entails three key components:

• The age at first reproduction (reproductive maturity)

• How often the organism reproduces (frequency)

• How many offspring are produced per reproductive episode

Understanding life history involved learning about how organisms ________________ and then characterizes differences in their __________

survive to reach reproductive age; reproductive strategies

Two different species and their different age of first reproduction

• Loggerhead turtles typically
  begin reproducing when
  they are about 30 years old

• Coho salmon first
  reproduce when they are
  only three or four years old

Organisms vary in how often they ________

reproduce

What is semelparity?

Organisms undergo a “one-shot” pattern of reproduction

• One very large reproductive event

(octopus, salmon, small marsupials)

Name the two types of reproductive frequencies

Iteroparity and Semelparity

Which reproductive pattern only happens once

semelparity (semel = once)

What is iteroparity?

Organisms undergo repeated reproductive events throughout their lifetime

• Fewer offspring

• Increased investment per offspring

(Cichlids, elephants, albatross)

Which reproductive pattern exhibits increased investment per offspring and fewer offspring?

Iteroparity (intero = again)

There is variation in the _________ of offspring produced per reproductive event

number

EX) White rhinoceros produce only one calf per reproduction
Insects and many plants produce large numbers

Name the two factors that impact the number of reproductive events

1. Probability adult will survive between reproductive events

2. Survival rate of offspring

   1. Low survival (Semelparity)

   2. High survival of adult and offspring (Iteroparity)

Which survivorship curves exhibit iteroparity strategy

Type I and some Type II

• Reproduce many time over a single life span

• High survival until late in life

Which survivorship curves exhibit a semelparity strategy?

Type III and some Type II

• Reproduce single times over a life span, minimal parental investment

• Low survival until later in life

Why do trade-offs occur?

Because organisms do not have access to unlimited resources

Because fundamental difference between what is good for the parent and what is good for the offspring

Use of resources for one function can _________ the resources available for another function

reduce

• Cannot simultaneously put resources into reproduction and survival

• Selective pressures influence trade-offs between the number and size of offspring

Caring for young can impact ___________

survivorship

• Caring for a larger number of young reduced survival rates of parents in Eurasian kestrels.

• Require help from both parents to keep
  young alive – many resources needed.

________ pressures influence trade-offs between the number and size of offspring

Selective

What are selective pressures?

evolutionary force that causes a particular phenotype to be more favorable in certain environmental conditions. Selective pressures are considered forces that drive evolution via natural selection

Young have a low chance of survival —> will produce ________ small offspring

many

• Plants that colonize distributed environments (dandelions), usually produce many small seeds

Parents produce relatively few offspring —> Invest _______ energy into each offspring and _________ the probability of survival for each

more; increases

• Brazil nut trees produce large seeds packed with nutrients that help seedlings become established

What is K-selection

Life history traits that are advantageous when

• Population size sits around K (carrying capacity)

• Density is high

• Constant conditions

• Resources are low

• Competition is strong

• Large size — low reproductive rates

While K-selected organisms stay near ___________, r-selected species population sizes tend to oscillate (or boom-best)

carrying-capacity

What are r-selection

Life history traits that are advantageous when:

• Population size oscillates around K (boom-bust)

• Density is low

• Little competition for resources

• High reproductive rates

• Fast maturation (small)

• Rapid colonizing ability

Name some K-selected species

Elephants, sharks, humans, whales, parrots, eagles

Name some r-selected species

Crabs, mussels, fish, mice, rats

Logistic growth appears in the shape of an

S

Exponential growth appears in the shape of a

J

When does exponential growth occur

When there are no limitations (unlimited space and resources)

Equation for population growth

dN/dt = B — D

where…

dN is the change in population size

dt is the time interval

B is the birth rate

D is the death rate

EX) Births = 120 cichlids in one year, Deaths = 20 cichlids in one year

So, 120 cichlids/year — 20 cichlids/year = Growth by 100 cichlids/year

To get per capita growth rate or r value, you need to…

population growth rate / population (N)

EX) 100/1000 = 0.1/year

With exponential growth, per capita growth rate ( r) does not change even if population gets too _______

large

Equation for exponential growth

dN/dt = rN

per capita growth rate ® does not change even if population gets large

Equation for ligistic growth

dN/dt = rN (K —N/K)

What is logistic growth

occurs when there are limitations

(limited space, resources etc.)

Carrying capacity = ____

K

Number of individuals of a species that can be supported by the resources with a given area

per capita growth rate = _________

r

Example of an S-shaped curve graph

Paramecium
• Growth of laboratory populations of some small animals and microorganisms fit an S-shaped curve if resources are limited
• These populations are grown in a constant environment lacking predators and competitors