Population Ecology: Life History, Distribution and Abundance

Question 1

Define life history and life history strategy.

Answer 1

life history - a record of major events relating to an organism’s growth, development, and reproduction
life history strategy - overall pattern in the timing and nature of life history events, arranged across all individuals of a species

Question 2

List the different ways that life history can vary within a species.

Answer 2

1. genetic differences
2. environmental differences
   phenotypic plasticity - a single genotype can produce different phenotypes under different environmental conditions (i.e. tusk diameter and height differs in elephants in cool and desert climates)
   allometry - study of how the characteristics of an organism change in relation to body size

Question 3

Define metamorphosis.

Answer 3

the transformation from the larval form to adult form occurs in distinct stages

Question 4

What are the types of sexual reproduction?

Answer 4

anisogamy - gametes are of different sizes; results in differential investment of reproduction
isogamy - gametes are the same size

Question 5

What terms are used to describe egg output and parental care strategies? Provide examples.

Answer 5

r-selected - typically smaller in size with shorter lifespans; mature early with no parental investment; allows for high population growth rates (i.e. oysters)
k-selected - typically larger in size with longer lifespans; delayed maturation and significant parental investment through gestation time (i.e. apes)

Question 6

What terms are used to describe the number of times and organism is able to reproduce in its lifetime?

Answer 6

iteroparous - capable of reproducing many times during its lifetime
semelparous - capable of reproducing only once in a lifetime (i.e. praying mantis, salmon, agave plant)

Question 7

What are the trade-offs of reproduction?

Answer 7

1. number of offspring vs. size of offspring (i.e. fence lizards)
2. current reproductive investment vs. likelihood of future successful reproduction

Question 8

How does age of sexual maturity affect offspring of iteroparous organisms? How does size affect offspring of iteroparous organisms? Provide an example.

Answer 8

earlier reproductive age = more offspring
larger size = greater reproductive capacity (number of eggs that can be produced)
i.e. atlantic cod can produce exponentially more eggs at larger lengths, but due to overfishing, smaller fish are more successful at reproducing

Question 9

Define senescence.

Answer 9

decline in physiological function of an organism with age; can be caused by reproduction in semelparous species (i.e. salmon and octopus)

Question 10

Define dispersal and dormancy. Provide examples of each.

Answer 10

dispersal - movement of organisms or propagules from their birthplace (i.e. the further the seeds of a dandelion are dispersed by the wind, the more successful they will be because there is less concentrated competition for resources)
dormancy - a state of suspended growth and development in which organisms can survive unfavorable conditions (i.e. brine shrimp eggs)

Question 11

Provide examples of larval adaptations.

Answer 11

protection (i.e. setae in marine worms)
consuming more food (i.e. mouth hooks and liquifying enzymes in maggots)

Question 12

Define paedomorphosis and provide an example.

Answer 12

a delay in development where organisms may reach sexual maturity before reaching adult form; an organism may retain juveniles or larval traits into adult life stages (i.e. axolotls typically never leave the larval stage because they lack thryoid hormone because larval stage = regeneration, underwater, etc.)

Question 13

Describe life cycle shifts in clownfish.

Answer 13

sequential hermaphroditism - sex changes during the course of the life cycle; thought to be timed to take advantage of the maximum reproductive potentials of the different sexes at different sizes (larger females can produce more eggs so their offspring have a better chance at survival - smaller males are more easily able to produce sperm cells)
clownfish regulate their growth rates to prevent social conflicts

Question 14

Define distribution and abundance.

Answer 14

distribution - the geographic area where individuals of a species occur
abundance - the number of individuals of a species in a population or given area; can change depending on time and space (i.e. european starlings have become invasive in North America because of a small founding population released in central park by Shakespeare enthusiasts)

Question 15

What factors determine population distribution and abundance? Provide examples of each.

Answer 15

abiotic - substrate type, climate, moisture, etc. (i.e. creosote bushes are tolerant to both dry conditions and cold temperatures, so they are broadly distributed across deserts; saguaro cacti are tolerant to dry conditions but NOT cold temperatures, so their distribution is much more narrow)
biotic - the presence of different organisms and the interactions they have with one another (i.e. drop in population of wolves lead to increase of deer due to lack of predation, which caused the browse line to be cleared of undergrowth; the distribution of plant growth is determined by the distribution of deer)
combination of biotic and abiotic (i.e. a species of barnacle can survive temperature shifts within a certain range, but they are not found within the full geographic range because of competition with other barnacles)

Question 16

Provide examples of combined evolutionary and geological history.

Answer 16

1. both the North Pole and Antarctica are technically within the suitable temperature range for polar bears, but because they evolved from brown bears near the North Pole, they do not cross unsuitable environments to go inhabit Antarctica
2. fossil record shows that lungfish were present and broadly distributed during the supercontinent pangea; when the continent broke apart, the populations were isolated across three separate continents
3. when landmasses drifted apart, each carried a population of marsupial mammals. over time, the ones in australia evolved

Question 17

Define dispersal limitation.

Answer 17

species are constrained to certain geographic areas because dispersal of seed or larvae has a small range; islands often do not have species from mainland due to dispersal limitation; density can affect dispersal (i.e. wingless bean aphids cannot disperse as well as the winged forms which can travel longer distances, so when density is higher in original populations, more winged forms are produced to encourage dispersal)

Question 18

Define geographic range. Provide examples of each type of geographic range.

Answer 18

geographic range - the entire geographic region over which a species is found
cosmopolitan - very wide distribution; across the entire globe or continents (i.e. great white shark)
endemic - relates to distribution that is unique to an area (i.e. koala bears)
seasonal ranges in migrant species (i.e. monarch butterflies migrate over several generations; range is restricted by milkweed plants as primary food source and temperature range during seasons)
breeding ranges in some species (i.e. fish and birds)

Question 19

Why might a species have a patchy distribution within a large range? Provide examples.

Answer 19

climate constraints allow for a wide geographic range, but limitations from biotic and abiotic factors in some areas will result in a patchy distribution (i.e. a type of buttercup that is restricted to glade regions where there is dry, rocky soil) (i.e. red kangaroos have a high habitat range, but abundance varies greatly)

Question 20

Define dispersion. Provide explanations of each dispersion pattern.

Answer 20

dispersion - spatial arrangement of individuals within a population; may change across seasons
regular dispersion pattern - often caused by interactions between individuals of different species (i.e. territorial carnivores) (i.e. creosote bush can secrete some chemicals within a radius that prevent other plants from growing near them)
random distribution pattern (i.e. dandelions and other generalists often occur randomly because they are not constrained by specific environmental conditions)
clumped distribution pattern - occurs when recourses are restricted or unequally distributed in a specific area (i.e. honey bees in hives)

Question 21

Define relative population size. Define the different methods for determining relative population size.

Answer 21

relative population size - estimate of total abundance of species
area-based counts - measure a particular area and then count the number of individuals within the area; common for immobile or sessile organisms (i.e. coral)
mark-recapture - a subset of individuals are captured, marked with a tag or radio transmitter, and released; common for migratory animals (i.e. birds)
distance methods - the number of individuals within a random transect that crosses a population area can be converted into a larger estimate