Ecology Lesson 2 Flashcards
Population Density can do what?
Affect birth and death rates. No population can grow forever because not enough space/resources. The density tells us how many people are fighting for the same resources.
Sea Otters
Live in groups and very social. Forage (look for food) alone but sleep/rest together. Young nursed and carried by mother for 4 to 8 months, mother care a lot for baby. Found on pacific coast. They use kelp to stay in places. Vert smart. They use tools like rocks to get things open and to get things off the sea floor.
What do sea otters feed on?
Urchins, clams, snails, crabs, fish.
Sea Otter former and present-day range?
Used to have a lot of otters but the population shrunk and some went extinct and had to be re-introduced.
How did the otter population decrease?
When the europeans arrived the fur traded happened (1700s to 1911). There is a lot of money in it, the less otters more expansive fur is because it’s rare. From 100 000 to 2000. Then in 1911 the harvest moratorium was signed (an agreement to stop hunting them). The last otter in BC in 1929, where it had to be re-introducted or translocation.
Amchitka Island
Very remote, part of US where war combat occurred (1940s). They was lots of otters there. Then in 1947 there was a wildlife refuge as a lot of otters were there. In 1950s it was proposed for nuclear testing and they move the sea otters to BC because they use to live there.
The translocation of otters to BC?
There was a high mortality in moving them. Most translocations from 1965 to 1972. But the 90 otters were introduced to Vancouver island.
Otters in BC
Because of the unconstrictied environment and there was no other otters there, there was exponential growth from 1977 to 1995. r=0.19. Then the growth rate slowed to r=0.08.
Why did the otter grow rate slowed?
Resources become limited, Food & space, Sea otters compete for food. Because of the increased amount of sea otters (aka intra-specific).
Intra-specific competition
Competition for resources among
individuals of the same species.
Carrying capacity (K)
The number of individuals of a population that an environment can support. The limit.
What does the K for otters depend on?
Length of coastline
Suitable habitat
Suitable food
Birth rate of sea otters?
Per capita birth rate doesn’t vary
with density. Birth rate is density independent. Still have the same number if pups no matter how many there are.
Death rates of sea otters?
Thin mothers: pups don’t survive. Pup death rate increases with density. Pup death rate is density-dependent. Can’t invest as much into each pup.
Equilibrium Density
Equilibrium if birth rate (b) = death rate (d) (aka carrying capacity). b>d is r>0. b<d is r<0.
Density-dependent regulation
The density the number of individuals is regulating the population size itself.
Regulated population
Returns to equilibrium. At least one density-dependent rate.
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.
Logistic growth model equation
dN/dt = rN (K-N)/K
(K-N)/K will stop the population from going infinity. It’s sigmoidal form.
If N is small relative to K (small population size)?
The population is close to exponential.
If N equals K (i.e. population is at carrying capacity)?
Population growth is 0.
If N is larger than K (i.e. population is above carrying capacity)?
The population growth is negative.
Carrying capacity in real populations?
Population fluctuates around K. Density-dependence not perfect. Environment changes, there is disease, boom in regulation. (ie. wolf-moose impact each other and it’s predator-prey).
When does population growth slow?
As the population approaches K.
Life history strategies
The best way to pass on the genes. ie. sea urchins have several million eggs per year, while sea otters have 1 pup per year. There is no perfect strategy it depends in context and environment and other species.
Why such huge differences in life history strategies?
Maximizing fitness: maximizing contribution to the gene pool of the next generation.
Reproduction involves trade-offs
More offspring -> less energy put into
each one (less hardy, resilient, and mortality is likely to higher). Energy includes offspring size, parental care. Larger offspring with more parental care are more likely to survive. (tougher well nourished).T
Trade-Off
Many low quality (most do not survive). Few high quality (each
likely to survive). Different organisms take different route for this.
r-strategy
Maximize number of offspring.
Smaller offspring. No parental care.
K-strategy
Maximize offspring survival. Larger offspring. Parental care.
Advantage of strategy depends on what?
The environment, why one isn’t exactly better than the other.
r-strategy advantageous where quality matters little, like?
Physically harsh environments. Unpredictable environments. Most offspring will not survive anyway.
K-strategy advantageous where quality matters a lot, like?
Highly competitive environments, Predictable environments, Stronger more likely to survive, Provisioning/care increases survival.
r-strategists are in what kind of habitats?
Open / disturbed
- Roadsides, lava flows
Temporary
- Tiny ponds, cropland
Unpredictable
- Deserts (rain), grasslands (fire)
K-strategists are in what kind of habitats?
Permanent
- Rainforest, open ocean, large lakes
Resource limited
- Or crowded etc
r-strategists tend to be?
Invading and colonizing species.
K-strategists tend to be?
Strong competitors
Life history strategies Evolved through natural selection & differences in?
Environment, Population density (competition for resources), Availability of mates (sex ratio).
r-strategy: death rate varies with age (how?)
Most young die – low survival. But adults often live a long time –
high survival.
Differences in r and K strategy survivability?
r-strategy: young is low, adults is higher.
K-strategy: young is higher, adults is low very late in life.
(shown by survivorship curves)
Cohort method
Follows a group of individuals organisms or population of a species through time. It records there amount that are alive.
Types of survivorship curves
Type I: K-strategist. Produce few offspring, most survive.
Type II: A mix of both.
Type III: r-strategist. Produce many offspring, most die.
Mortality varies based on what?
How old you are and life history strategy.
Demography
Studying the affects of population age structure and population growth. They can infer what’s happening in human populations around the world.
Global population age structure pyramid
Divided by sex. Narrow when get older, and wide when young.
Canada pyramid
Wide at the boomers because more birth rate from more resources. Echo also a little wide (children of boomers). Birth rates declining.
0 – 4 years: males > females.
75+ years: females > males.
Death rates vary with age
High when baby, then drops a lot, then increases as gets older. Higher mortality for men. A 45 year-old is more than twice as likely to die as a 25-year old. 25 year-old male is ~3 times as likely to die as a 25-year old female.
Birth rate varies with age
30-34 is where births is highest. Used to be 10 years early but changed because education and resources.
Births and deaths vary over time in Canada
Both births and deaths have decreased.
Canada and Chine population pyramid
Both have Spindle shape: Boomer bulge, Echo generation in their late 20s, Large decline in birth rate in recent years.
Differences in population in countries?
Because difference in when people have kids, how many, and the opportunities they have.
Niger population
Little decline in birth rate. High death rate – concave shape.
India population
Birth rate declining. Lower death rate – convex shape.
How high is human population growth?
8.2 billion, became every high in 2000s. Global population growth rate
expected to continue to decline. Uncertainty in how many people there will be.
Total fertility rate (TFR)
Number of children per female over their lifetime.
Replacement TFR
2.1 children. At this TFR, births exactly replace deaths. Zero population growth. 0.1 because some kids die and some women chose not to have kids.
TFR in World and Canada?
Both decreasing. While Canada’s is less than 2.1, the population is still growing because of immigration.
Population inertia
A cohort of people who are of reproductive age still going to get these bulges and the cohort works it’s way through the population. This means the population weeps growing even when TFR is below 2.1. ie. in china, population kept growing because of age structure.
World population growth?
The world’s population is still growing, but rate of growth is
declining.
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.
