lecture 2 ecology Flashcards
population density – what does it effect
affects brith and death rate
sea otters
live in groups, look for food individually but sleep/rest together, heavy maternal investment – young is nursed and carried for 4-8 months.
what happened to sea otters
there is now gaps in distribution.
all startted in early 1700’s-1911 – this was the fur trade – europeans arrived, and population decreassed from 100,000 to 1000-2000
in 1911 an agreement was signed to limit/stop harvesting (harvest moratorium) – this was a bit too late for specific popultion as the last otter in BC was driven to extinction in 1929.
what did we do to fix this extinction of otters (think about process, where, why it didnt work)
currently there is a population of otters in BC, but how?
translocation/reintroduced.
otters were moved from one place to another to try to reestablish a population that has been driven extinct.
in 1947 – Amchitka land was made into a wildlife refuge for tters as it was a very remote land – that didnt last – 1950s the land was proposted to be suitable for nuclear testing, so otters were moved to BC where there had been ottewrs in the past. – this was good, there was no competition between other otters, but growth rate soon slowed because of more competition, food and space, and resourced ultimately became limited.
carrying capactiy
number of individuals of a population that an environment can support
what happens as the number of sea otters increase
less food – lower population growth rate (r)
what do we look at to determine the birth and death rates of sea otters
we look at density dependent births and deaths
birth rates in otters
the birth rate in otters is density-independent, meaning the birthrate does not depend on the number of individuals in the population
death rates in otters
the death rate is density dependent. this means that the death rate is dependent on the number of individuals in the population. this could mean limited space, resources, and an increase in competition for food. whixh leads to the mothers investing less in their pups, starvation..
equilibrium density
if birth rate equals death rate – will be the intersection of both lines.
density dependent regulation
factors that influence population size based on the population density. in other words, basically density is regulating population size.
regulated population – what is needed.
at least one density dependent rate – this returns population to equilibrium
limits to population growth – summary
growth slows as resources become less abundant, this is because birth rates decline and/or death rates increase. density dependent births or death rates regulate populations around an equilibrium
Modeling density dependent growth – equation
the logistic growth model
dN/dt = rN(K-N/K)
if N is smaller than K (logistic growth)
if N is small relative to k, carrying capacity is fixed (1) – population growth is CLOSE to exponential
if N = K (logistic growth)
population will be at carrying capacity, the growth will be constant
If N is larger than K (logistic)
population will be above carrying capacity, population growth will be negative
carrying capacity in real populations
population fluctuates arounddd K, it is never perfectly stable – there are still some things in the environment (predators, disease, environment changes)
Life history changes urchins vs otters
urchins – several million eggs per year
otters – 1 pup per year
life history strategies
maximizing fitness, the contribution to the gene pool of the next generation. – doesnt necessarily mean maximizing number of offspring
reproduction tradeoffs
low vs high quality
low – most do not survive
high – all likely to survive
different strategies
depend on environment and ecosystem (k and r)
k strategy characteristics
carrying capacity, maximize offspring survival, larger offspring, parental care.
– quality of offspring matters a lot, highly competitive environment, predictable environments, stronger, more likely to survive, parental care increases survival.
r strategy characteristics
maximumizing growth of population, max number of offspring, smaller offspring, no parental care.
– advantage where quality of offspring matters very little, physically harsh environments, unpredictable environments, most offspring will not survive anyway
organisms of r strategies tend to be found in habitats that arE:
ope/disturbed – roadsides, lava flows.
temporary – tiny ponds, cropland
unpredictable – deserts (rain), grasslands (fire)
the organisms tend to be invading species, colonizing species
organisms of k strategies tend to be found in habitats that are:
permanent – rainforests, open ocean, large lakes.
resource limited – crowded, etc..
the organisms tend to be strong competitors.
life history strategies summary
evolved in natural selection, differences in: environment, population density, availability of mates (sex ratio)
– always involve trade offs :
few vs many offspring
parental care vs no parental care
reproduce early vs late, many times vs only once.
demography
study of populations focusing on birth rates, death rates, age structures, and population growth
r strategy relative to demography
produce many offspring therefore they have a high birth rate. their death rate varies with age, most young die, so they have a low survival, but the adults often live long, they have a high survival
k strategy relative to demography
maximize fitness, the young have a high sruvival because of the parental care, but the adults have lower survival due to old age, and post reproductive years.
draw a survivorship cure for r and k strategy of cod and whales, label and interpret
whale on top (k) and cod on bottom (r), r represents that all are alive at age 0, but they all rapidly die off, k represents that all alive at 0, and overtime, adults die off due to old age.
what do we use to construct a survivorship curve
the cohort method – tracking group of individuals over time
types of survivorship curves
type 1, type 2, and type 3.
type 1 – k-strategist, produce few offspring, most survive
type 2 – steady/constant decline
type 3 – r-strategist, produce many offspring, most die.
age pyramid
divided by sex, age is increasing by 5 year incriments. measures the population of each age groups
death rate stats in canada – males
they are slightly higher than females, could be due to biological interruptions, cultural factors, risk taking..
what are the two things that contribute to populatiion structure
birth rate and death rate
spindle shape
draw. Canada and china. boomer bulge, echo generation in their late 20s, large decline in birth rate in recent years.
concave shape
Niger, mortality rates are higher, LITTLE decline in birth rate, higher death rate
Convex shape
India. Birth rate declining, lower death rate.
total fertility rate TFR
number of children per female over lifetime
CANADA TFR
canada is growing without high birth rate (immigration exceeds emmigration so positive net migration) – the TFR is fairly low, therefore without immigtration, canadas population would be decreasing.
replacement TFR
2.1 – we would get a population growth of 0
population inertia – china
population may keep growing even after TFR declines due to AGE STRUCTUREEEE – CHinas population continued growing after 1 child policy, because cohorts were at reproductive ages, therefore pop was still increasing but slower.
global growth rate and population
right now at around 1% growth rate, we will most likely get to 10 billion later on in century
word population growth summary
– the worlds 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 (those wo are entering reproductive stages) keep growing for a time after they reach replacement TFR. (before population stabilizes)
