Flashcards
BIOL368: Lecture 6
Cards in this deck (16)
- 1Define a population.Multiple individuals of the same species.
- 2What are the basic processes that determine if a population will shrink or grow?1. Births
2. Deaths
3. Immigration
4. Emmigration - 3Processes that regulate a population can be intrinsic or extrinsic. What is the difference?Intrinsic processes are things happening within the population (births, deaths, etc). Extrinsic processes are things happening outside (weather, climate, etc).
- 4Edmond Halley developed an equation to describe how a population changes year by year with consideration to births and deaths. What is that equation?Nt+1=Nt - deaths + births
- 5Leonhard Euler modified Halley's equation to take into account immigration and emigration. What is that equation?Nt+1=Nt(1 + r)
Where r = i - e + b - d - 6Haldane observed that if r was even slightly > or < than 1, given enough time a population would either grew exponentially forever or crash. Despite this, r is typically close to 1. Why?Processes regulating a population size prevent it from becoming too big or too small (most of the time).
- 7In Thomas Malthus's "An essay on the Principle of Population", he said that populations grow _______, while food grows _________. What implications does this have?Populations grow exponentially, while food grows arithmetically. The implication being that populations will inevitably reach a point where this isn't enough food for everyone, slowing growth and causing hardship.
- 8Pierre-Francois Verhulst introduced logistic growth into population modelling. Explain how it works.Population growth is approximately exponential when N is small. As N approaches the carrying capacity (K), growth slows down and eventually plateaus when K is reached. On a graph the line will curve up at the start and flatten out as N approaches K.
- 9The impact of events can be either density dependent or density independent. What examples were used in the slides for each?The spread of bird flu in a human population was used as an example of a density dependent phenomenon. The more people within proximity of each other the more chance there is for the virus to spread.
Unseasonal frost effecting a population of aphids was used as an example of a density independent phenomenon. The name of aphids per unit of area will not impact the odds of any individual aphid surviving. - 10Robert May, while using equations similar to Verhulst's, observed chaotic behaviour when certain parameters were within a specific range. What is chaos?Its when a systems is so sensitive to variation in its initial state predictions become impossible to make. This is due to wild variation in outcomes depending on initial settings.
- 11Explain the Allee effect. What can cause it?The Allee effect is negative change in r at low population levels. At low population levels it can be difficult to find a mate, defend yourself or hunt for food without a lot of other individuals to help.
- 12Assuming a strong Allee effect, what will happen to a population if it goes down to N crit?Below N crit the population does not have enough members to keep r positive. Without outside intervention a population below N crit will go extinct.
- 13Historically, there have been 3 main schools of thought regarding regulation. What are they?1. Density dependent regulation.
2. Density independent regulation.
3. Intrinsic & Behavioural factors. - 14True or false: Density dependent processes can operate at low, as well as high population densities?True. The Allee effect is a phenomenon where the r value for a population goes down at low enough population densities.
- 15What happens to a population if it overshoots its carrying capacity (K)?The population will likely crash, leading to chaotic dynamics.
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