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.