Evolution 2 Flashcards
What are processes that affect population size?
Births, deaths, emigration and immigration.
What are intrinsic factors that affect population size?
Factors such as the age of first reproduction - directly related to the individual and are built into the genetic basis of the individual.
What are extrinsic factors that affect population size?
External factors such as predation and natural catastrophes.
What are density dependent factors?
Factors that affect the size of the population in a way dependent on the size of the population such as the effects of food supply.
What are density independent factors?
Factors that influence populations independently from population size such as the effects of weather and catastrophic events.
What is the population change dependent on?
Births-deaths.
What is more useful than calculating births and deaths over a certain time?
Per capita birth/death rate.
What is r?
Intrinsic growth rate.
What is the exponential population growth curve?
dN/dt = r (instant)N where dN is a small change in the number of individuals and dt is a small change in time.
What do we know if we know r?
The population dynamics.
What prevents populations from growing indefinitely?
Limited resources.
When does growth start to decrease?
As the number of individuals approaches the carrying capacity of the environment.
What other factors beside the carrying capacity are important?
Lagtime in the response to change in conditions.
What is population growth linked to?
Life history traits.
What are life history traits determined by?
Evolutionary constraints and natural selection.
Example of animal that lives for a short time but produces lots of offspring?
Flies.
Example of animal that lives for a long period of time but only produces a few offspring?
Albatrosses.
What is life history?
The pattern of allocation to growth, development, reproduction, survival etc.
What does semelparous mean?
Only one reproductive season.
What does iteroparous mean?
Have many reproductive seasons.
What are some life history traits?
Age and size at reproduction, number of reproductive seasons, life span, number and size of offspring.
What are the predictions for the perfect life history?
Mature at birth, continuously produce high-quality offspring in large numbers and live forever.
Why does the perfect life history not exist?
The amount of resources available to an organism is finite - this generates trade offs.
What may a mutation result in in terms of life history strategies?
There may be an increase in the focus on reproduction rather than maintenance or growth.
What is a common trade off?
Life span vs reproductive output.
Why is life span different from senescence?
Life span is only determined by senescence if an organism lives in a protected environment.
What is senescence?
The condition of process of deterioration with age.
Even if an organism could live forever, why doesn’t it?
Due to random chance, predators and parasites.
What is life span a result of?
An organisms genetics and its environment.
What is a result of the factors influencing lifespan?
The probability of reproducing reduces with age.
Why do organisms not always reproduce really early?
Larger individuals produce more and/or larger offspring.
What happens if reproduction occurs too early?
There is not sufficient resources and there is selection to reproduce later.
What happens if reproduction occurs too late?
Death comes before reproduction and there is selection to reproduce earlier.
What does natural selection favour?
Maximum total fitness - for organisms that reproduce multiple times, the number of progenies is important, and not just the size of the clutch.
How does mortality rate differ between deer nursing and deer not nursing?
Mortality for deer that are not nursing is much less than for those that are nursing.
What did experiments with male drosophila show about reproduction?
Males kept with inseminated females/no females lived longer than those kept with virgin females.
Why can large numbers of large offspring not be produced?
There are limited resources.
What does natural selection favour in terms of clutch size?
The clutch size that produces the most surviving offspring.
What is experimental evidence for the ideal clutch size?
Experiment with a magpie - showed that the modal clutch size of 7 is optimum- maximises the size of the offspring.
Why do extremes still exist between number and size of offspring?
Different environments may favour different strategies.
What are r selected populations?
They reproduce rapidly and use resources wastefully. Their success relies on finding new resources elsewhere.
What are K selected populations.
They breed slower and use resources more efficiently.
What are the characteristics of R selected populations?
They have small organisms, short life time, large progenies, small offspring and high dispersal. There is low competition, high predation.
What are the characteristics of K selected species?
They are larger individuals that are slow to mature and have few large offspring. There is high parental care and competitive environments. There is a high risk of mortaility in these environments.
