Ecology: Lecture 2 Flashcards
Population density affects?
Population density (individuals/area) can affect birth and death rates.
Why does population density affect birth and death rates?
Latin can be exponential forever, as there are not enough space nor enough resources.
- How tightly are individuals packed in, and how does this lead to competition for space and resources affect the birth and death rates.
What do sea otters do?
They live in groups, forage alone, sleep/rest together, and their young are nursed and carried by their mothers for 4-8 months (heavy maternal investment)
What do sea otters feed on?
They have a variable diet, feeding on urchins, clams, snails, crabs and fish.
Are sea otters intelligent?
Yes, they use rocks to open urchins and get the food inside, wedging items that are stuck off of the seafloor.
How has their range changed?
The current distribution has changed a lot recently. They were deteriorating in certain areas, yet translocated later at an attempt to reinstate the population. Now, there are gaps in the historical population and the current population.
What happened to cause the change?
-The fur trade lasted from the 1700s to 1911.
- In 1911, there were 1000-2000 otters left (100000 originally). A harvest moratorium was instated to help limit hunting.
- The B.C. coast was down to their last otter in 1929, and has since been reestablished.
What happened on Amchitka Island?
In 1940s there was a war, and was an air base in WW2.
- It was made a wildlife refuge in 1947, then, in 1950 it was proposed for nuclear testing. The otters were moved to another part of the their range at this point.
Nuclear testing and see otter translocations?
Nuclear tests were done in 1965, 1969, and 1971.
- Throughout this time, many otters died. They learned how to successfully relocate the population in this time.
- Most of the translocations occurred from 1965-1972.
How many otters were introduced to Vancouver Island?
89 otters were introduced to Vancouver island between 1969 and 1972.
How did the population of sea otters grow on Vancouver Island?
They were experiencing exponential growth, with limited competitors and abundant resources.
From 1977-1995, r was 0.19.
When did the population of sea otters change in the ‘r’
The r value went from 0.19 to 0.08, indicating that the population growth was slowing. This occurred in 1995.
Why did the population growth rate slow down after 1995?
- Resources became limited
- Food and space became limited
- Sea otters had to compete for food.
What is the competition between sea otters known as?
Intra-specific competition
- Competition for resources among individuals of the same species.
What was the growth rate and population in 2013?
In 2013 there were around 5600 otters.
- The r was 0.05 at this time (2008-2013)
What is carrying capacity?
Carrying capacity (K) is the number of individuals of a population that an environment can support.
What was the K for the sea otters?
K = ~8000 sea otters
What are the factors behind the K for the sea otters?
- Length of the coastline
- Suitable habitat
- Suitable food
How does the birth and death rate change?
- Sea otter numbers increase
- Less food
- Lower growth rate (r)
What is r equal to?
r = b - d
b = births
d = deaths
Does the per capita birth rate vary with density?
No, birth rate is density independent.
- Females still have the same amount of children with a large population.
Does the per capita death rate vary with density?
Yes, it does; death rate is density dependent.
- There are thin mothers, and pups don’t have enough resources to survive: they cannot invest enough energy
- Pup death rate increases with density.
What is equilibrium density?
The equilibrium if the birth rate equals the death rate. This equilibrium is the carrying capacity.
What is density-dependent regulation?
The density of the number of individuals regulates the population size itself.
Equilibrium with density dependence in birth rates as well?
A regulated population:
- returns to equilibrium
- has at least one density-dependent rate.
What happens when b > d and r > 0
the population increases in number
What happens when b < d and r < 0
The population decreases in number
What are the limits to population growth?
- Growth slows as resources become less abundant.
- This is because birth rates decline and/or death rates increase.
- Density-dependent birth or death rates regulate populations around an equilibrium (K, carrying capacity)
How do we model density dependent growth: logistic?
dN/dt = rN (K-N)/K
dN/dt = change in population size
rN = growth rate with unlimited resources
(K-N)/K = effect of limited resources
What is the definition of carrying capacity: K?
Number of individuals of a population that an environment can support.
What is the effect of limited resources if N is small?
- If N is small relative to K (small population size) than (K-N)/K ~ 1.
Therefore, dN/dt = ~ rN
When N is small?
The population growth is close to exponential.
What is the effect of limited resources is N equals K?
(K-N)/K = 0
Therefore, dN/dt = 0
When N=K?
When N is equal to carrying capacity, population growth is zero.
What is the effect of limited resources if N is larger than K?
It is less than 0, meaning that dN/dt is negative.
When N>K?
When N is above the carrying capacity, population growth is negative.
The population fluctuates around?
The population fluctuates around K, as density-dependence is not perfect.
K in real populations?
- There might be a changing resource availability, disease, interactions with other populations, etc.
What happens when the population fluctuates?
When the Population fluctuates, the environment changes.
What is the carrying capacity?
The number of individuals that an be supported in a given environment.
When dos the population growth slow?
The population growth slows as the population size approaches K.
What is the logistic model?
The logistic model is one way to model population growth in a limited environment.
What changes population growth?
Factors such as a changing environment cause population growth to differ from ideal logistic growth.
Is there any perfect strategy for population growth?
NO!
When one has several million eggs per year…?
The chance of exponential growth is high.
When one has 1 pup per year…?
The chance of exponential growth is low.
What are life history strategies?
The goal of life history strategies are to maximize contributions to the gene pool of the next generation.
Does maximizing the contributions to the gene pool mean maximizing offspring?
NO!!! Not necessarily.
Reproduction involves what?
Reproduction involves trade-offs.
Why are there trade-offs?
There is a finite amount of energy in the world.
Energy includes offspring size and parental care.
More offspring means?
less energy put into each individual offspring.
Many low quality = most don’t survive
Larger offspring means?
More parental care and higher chance of survival.
Few high quality = likely to survive.
What is the r-strategy?
Maximize the number of offspring.
- Smaller offspring
- No parental care.
What is the k-strategy?
Maximize offspring survival
- Larger offspring
- Parental care
When is each strategy advantageous?
The advantage of the strategy depends on the environment, therefore neither can completely dominate.
When is the r-strategy advantageous?
The r strategy is advantageous when quality matters little
- Physically harsh environments
- Unpredictable environments
- Most offspring will not survive anyways
When is the k-strategy advantageous?
K strategy is advantageous when quality matters a lot:
- Highly competitive environments
- Predictable environments
- Stronger and more likely to survive
- Provisioning/care increases survival
Where are r strategists found?
- Open/disturbed habitats (Roadsides, lava flows)
- Temporary habitats (Tiny ponds, cropland)
- Unpredictable habitats (Deserts (rains) and grasslands (fire))
Where are k strategists found?
- Permanent habitats (Rainforest, open ocean, large lakes)
- Resource limited habitats (or crowded, etc)
r-strategists tend to be…?
Invading species and colonizing species.
k-strategists tend to be…?
Strong competitors
How did life history strategies evolve?
They evolved through natural selection and differences in:
- Environment
- Population density (competition for resources)
- Availability of mates (sex ratio)
What do life history strategies involve?
They always involve trade-offs:
- Few vs. many offspring
- Parental care/no parental care
- Reproduce early vs. late, many times vs. only once
r-strategy?
Produce many offspring
- maximize offspring and. other concerned with quality/survivability
r-strategy death rate?
Their death rate varies with age:
- Most young die - low survival
- Adults often live a long time, high survival
k-strategy death rate?
Young have high survivability and adults have low survival late in life.
Constructing a survivorship curve: Cohort method?
Follow a group of individuals (organisms or populations) through time.
Compare number alive and proportion alive.
Survivorship curve?
Mortality varies with age and life strategy.
Type 1 survivorship curve?
K strategist: Produce few offspring yet most survive.
Type 3 survivorship curve?
r-strategist: Produce many offspring, most die.
Type 2 survivorship curve?
Mice example:
- Linear decline, fairly consistent.
- Steady death rate throughout lifespans.
Affect of age-specific birth and death rates?
- population age structure
- Population growth.
What is the study of demography?
The study of age, structure and how populations and growing and/or shrinking.
Global population age structure?
Age pyramid; more young people than old, decline as age increases
In canada?
Boomers have a large population, as well as the echo that consists of their children.
Death rates vary with?
Age and gender. Can be biological factors, risk taking or external factors.
Reading a survivorship curve?
Age specific death rates:
- A 45 year old is more than twice as as likely to due as a 25-year-old.
Age specific death rates:
- A 25 year old male is 3 times as likely to die as a 25 year old female.
What is a spindle shape for population maps?
- Boomer bulge
- Echo generation in the late 20s
- Large decline in birth rate in recent years.
Niger example?
Little decline in birth rate and a high death rate = concave shape
India example?
Birth rate declining and low death rate = convex shape
Total fertility rate (TFR)?
Number of children per female over their lifetime.
Replacement TFR?
2.1 children, at this rate births exactly replace deaths, and there is zero population growth.
TFR in the world and Canada?
The TFR is slowing down, and is why the human population will likely peak at 10 billion before declining.
Population inertia?
Still grows despite going at or below 2.1 TFR.
Why does Population inertia occur?
- Because of age structure (many young), populations often keep growing after reaching TFR = 2.1
World Population Growth Overview?
- The world’s population is still growing, but the rate of growth is declining (sometimes below TFR)
- Birth rates have declined in most countries, and many are at or below replacement fertility
- Age structure affects population growth. Young populations keep growing for a time after they reach replacement TFR.
What is the carrying capacity (K) for humans on earth?
We have likely already reached it:
- Efficiency in using resources
- how many resources there are
- rate that we are using resources.
Limits to population growth?
Population density can affect birth and death rates
Life history patterns?
Birth and death rates differ across species
Demography?
Birth and death rates differ with age.
