View
1.487
Download
0
Category
Tags:
Preview:
DESCRIPTION
Ch 35 notes
Citation preview
What is population?
• Group of individuals of the same species that live in the same area
Does population change?
• Sea otters, kelp, and sea urchins
•Kelp forests offer a habitat for sea otters
•Sea urchins feed on kelp
•Sea otters feed on sea urchins
• What do you think happens when sea otters are hunted?– Sea urchins increase or decrease?– Kelp forest increase or decrease?
• Sea otters are then placed on the endangered species list
• So now what happens to the population of sea otter?– Starts to increase
• How does this affect the kelp and the sea urchins?– Sea urchins start to get eaten again=decrease in #– Kelp increases b/c less sea urchins to eat them
But now we have a new hunter….
What happens to the sea otter, kelp, and sea urchins?
What does this tell us about population?
• Population changes
• There are many factors that influence a population– Natural – Unnatural
• Population density has a great impact on ecosystems
3 important characteristics of Population
• Geographic Distribution
• Density
• Growth Rate
***Population Age structure is also an important characteristic
Geographic Distribution
• AKA Range
• Describes an area inhabited by a population
• Can vary–Few cubic centimeters–Kilometers of the ocean
Density• # of individuals per unit area• Low density
–Cactus in desert
• High density–Other desert plants and succulents
Math Time
• Formula for calculating population density
• Population density=Number of individuals
units area
• Problem: Suppose there are 150 bullfrogs living in a pond that covers an area of 3 square kilometers. What is the density of the bullfrog population?
• 50 bullfrogs per square kilometer
Growth Rate• Many factors affect growth rate
Sampling Techniques
• How would we measure the population of a species?
• Impractical to count each and every one
• Variety of sampling techniques– Quadrants– Indirect counting– Mark-Recapture
Quadrants
• Involves marking off specific area, boundary• Count specific species within the boundary• Repeat in several locations within desired
ecosystem• Average the results to determine population
density• More quadrants sampled=more accurate
Indirect Counting
• Used for species that are too difficult to see or move around too quickly
• Does not involve counting organisms themselves– Count nests, burrows, tracks
Mark-Recapture
• Most common• Choose a study area• Trap/capture animals• Mark the captured animals and release back into
habitat– Markings are not to disturb organism
• After a period of time, recapture animals in the same study area
• Count marked and unmarked organisms
How to Estimate Population from Mark-Recapture Method
Total population= (# in first capture) x (# in second capture)
number of marked animals RECAPTURED
Limits to Accuracy• Involve making assumptions about populations
– Assumptions not valid=estimate not accurate• Quadrant
– Assumption:• Organisms distributed evenly in study area
– Problems• “Clumps”• Quadrant with clump vs quadrant without clump
– Minimize problem• Analyze how study population is distributed in order to choose appropriate quadrant
size• Mark-Recapture
– Assumption:• Both marked and unmarked animals have same chance of surviving and being
recaptured in second trial– Problem
• After being captured once, how do you think animals will behave?• Leads to overestimating population size
– Minimize problem• Minimize effects of trapping on organisms
3 Factors that affect population size
• # of births
• # of deaths
• # of individuals that enter or leave population
Population will increase or decrease depending on # of
individuals added or removed
• Have more births than deaths?– Population increases
• Have more deaths than births?– Population decreases
• Have equal amounts of births and deaths?– Population remains constant
What happens to the population when we….
Immigration
• “im”= in
• Migrate= to move from one place to another
• Immigration is the individual movement into an area
• Animals in search of mates and food in new areas
Emigration
• “E” means ‘out’
• Migrate means to move from one place to another
• Emigrate means individuals moving out of one place and into another
• Young wolves and bears leaving as they mature
• Shortage of food
Two types of growth
• Exponential growth– Individuals reproduce at a constant rate
• Logistic growth– Occurs when a populations growth slows or
stops after a period of exponential growth
Exponential Growth
• Occurs under ideal conditions with unlimited resources
• Think about exponents in math….• Starts slowly then sky rockets to infinity• Our graph will look like a J• Bacteria
Lets look at bacteria…
• Bacteria reproduce by splitting in half• Bacteria have a doubling time of 30 minutes• If you start will one bacterium, how many bacteria will
there be after the first 30 minutes?– 2
• After an hour?– 4
• After an hour and a half?– 8
• After two hours?– 16
• After 15 hours?– Over a billion
Logistic Growth
• As resources become less available, the growth of the population slows or stops
• S-shape curve
• What we usually see in nature
Carrying Capacity• The largest number of individuals that a given
environment can support• The part of the logistic graph after the
exponential growth…the flattening out• The point at which this flat line reaches the y-
axis is the size of the population when the growth rate reaches zero
• This doesn’t mean the population stops growing• Many factors slow the growth of plants and
animals…
Recommended