Population Ecology: module 4

Question 1

Do population or individuals evolve?

Answer 1

populations

Question 2

define a population

Answer 2

• a group of individuals of a single species living in the same general area
• rely on the same resources
• influenced by similar environmental factors
• interact with one another
• have demographic and genetic cohesiveness

Question 3

why would it be more difficult to census how many individuals a plant population includes sometimes?

Answer 3

plants have a dormant stage as seeds in the ground

Question 4

define the mark and recapture method

Answer 4

• capture individuals, mark them, release them, then later capture another sample
• proportion of marked individuals that you recapture will indicate the size of the population
• must ensure that the method does not cause mortality, as it will mess up your results

Question 5

Describe how people are estimating polar bear populations in Canada.

Answer 5

• genetically indentifying individuals who leave feces or hair behind
• it is a genetic mark and recapture method
• but they don’t have to capture anything
• indentify and re indentify indivduals by thier DNA

Question 6

describe what demographic and genetic cohesiveness means.

Answer 6

• demographic cohesiveness: shared environment and resources
• genetic cohesiveness: individuals breeding with one another

Question 7

how can a population grow or shrink, in a “measureable” way?

Answer 7

how many are born, die, leave (emmigrate), join (immigrate)

Question 8

why are chickadees easy to observe when defining populations?

Answer 8

do not migrate

Question 9

describe what a life table is.

Answer 9

• age (x)
• survival (Ix)
• births (bx)
• can calculate important population parameters
• Ro: reproductive rate (average number of offspring produced per female) (births and deaths)
• Generation time: products of age, times specific survival times and age specific birth, add them ip, and divide it by the reproductive rate, the average interval between the birth of an individual and the birth of its offspring.

Question 10

what does a shorter generation time mean?

Answer 10

shorter generation time has the potential to grow more quickly

Question 11

What is a survival curve? define each type of the survival curves.

Answer 11

• repersents the interaction between the species and the environment a species lives in, and the species’ evolved life history traits, which ultimately turn into natural selection
• Type I: invest heavily in the offspring, which results in high survival during early part of their life
• Type II: survivorship maintains relatively constant
• Type III: produce many tiny offspring, and have low prospects for survival

Question 12

what is investment in offspring as a trait?

Answer 12

evolves in relation to the timing of mortality in the environment

Question 13

when does exponential growth occur for a population?

Answer 13

• when a population of a species is growing without limits

Question 14

describe the logistic growth model

Answer 14

• as population size increases, the rate of growth slowss down to one, and population plateaus at the carry capacity (zero growth)
• when population size if very small, this term becomes equal to one, and the population grows near exponentially

Question 15

what could happen in a population where individuals have a hard time finding mates when they occur at very low density?

Answer 15

• population may not grow very exponentially when small as predicted by the logistic growth model, as it doesn’t work for them
• important when you are a conservation biologst trying to enhance the growth of an endangered species population

Question 16

what is the maximum productivity of a population in terms of new individuals?

Answer 16

when the population size is equal to exactly 1/2 of the carrying capacity

Question 17

What does keeping the harvesting population so that the population is half of the carrying capacity cause?

Answer 17

Maximum sustainable yield
(MSY)

Question 18

how would a death and birth rate change or not change with density independent or density dependent factors?

Answer 18

• density independent: does not change with poopulation density
• density dependent: does change with poopulation density

Question 19

what is population dynamics?

Answer 19

fluctuations in size from year to year for populations

Question 20

describe the cause and effect relation between predator and prey, with the lynx and the hare example.

Answer 20

• the population cycle of the predator, the lynx, lags behind the population size of the prey, the hare
• this might suggest that cycles are driven by predator and prey interactions
• developed two hypothesis: food shortage and predation hypothesis
• food shortage: the hare cycle is determined by a cycle in the availbility of food, so the lynx follows the abundance of hares
• predation hypothesis: hare cycle is driven by predation,

Question 21

what is meta population model of population dynamics

Answer 21

• a species in a habitat patch will go extinct there
• that vacant patch will be re colonized by individuals from a differently occupied habitat patch

Question 22

what are some insights that can be gathered from the meta population model of population dynamics?

Answer 22

• it is essential for species persistance that a species can move from an occupied patch to an unoccupied, but suitable patch
• species will only occupy some fraction of the availble habitate patches at any given time, but it needs unoccupied but suitable patches to persist on the landscape

Question 23

how are wildlife corridors helpful?

Answer 23

• maintain gene flor
• ensure viable meta population dynamics

Question 24

what are life history traits?

Answer 24

• characeristics of a species that directly affect population dynamics
• traits that are also likely to be the subject to quite strong natural selection
  *

Question 25

what is the principle of allocation?

Answer 25

given that resources and time are limited, there are going to be trade offs
* example: an individual acquires resources from its environment by photosynthesis or eating, and then it allocates those resources to competing functions like reproduction or growth
* resources allocated to reproduction take away from the resources availble for maintenance and growth, therefore we see a trade off between different components of fitness or different traits that influence fitness

Question 26

what is a semelparous species? what is iterospecies? describe them.

Answer 26

• semelparous species: individuals will reproduce once and then die
• iterospecies: species where individuals reproduce many times

Question 27

describe why an individual being semelparous may be favoured.

Answer 27

if an adult individual has a low probabilty of survivng compared to a newly born juvenile, then it is better for the individual to devote all of its resources to the production of new juveniles and then die