# BLG 144 Lecture Notes - Lecture 21: Net Reproduction Rate, Albertosaurus, Exponential Growth

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15 Aug 2016
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BLG 144 – Chapter 52: Population Ecology
Population—a group of individuals of the same species living in a same place at a same time.
Population ecology—how and why the the number of individuals in a population change over time.
Demography—the study birth, death, emigration and immigration that determine the size and structure of a
population.
Population growth - growth rate is a function of b, d, e and i
- conservationists use data to manage threatened species
Life tables—summarizes the probability that an individual will survive and reproduce in any time of its life time
Survivorship—the proportion of offspring produced that survive at a particular age. It’s cohort—a group of
individuals with with same age and time.
lx = Nx ÷ N0
Three types of curve: - Type I – high survivorship; most reach max life span of the species i.e., humans (low
fecundity = high parental care)
- Type II – constant death rate i.e, fish (high fecundity = low parental care)
- Type III – high death rate in the early stages of life then high survivorship as mature i.e,
plants
Fecundity—the number of females produced by each female in a population (age specific)
R0 = sum lx • mx
- R0—the net reproductive rate of a population/ gen time
- R0 > 1, pop increase; R0 < 1, pop decrease
Albertosaurus Life Tables – are they Type III?
- no b/c the results show they are modified Type II and they have high juvenile survivorship but after
reaching a reproductive age they die; they were also compared with other orgs that lived in the area
Fitness Trade Off - occur because every individual has a restricted amount of time, energy and resources
at their disposal; they can’t have babies all the time b/c they too costs too much
Life-history—how orgs portions/use their resources for growth, reproduction and survival abilities
Pop growth rate—change in # of individuals over per unit time.
- no immigration/emigration occurring then growth rate = N • r
- r—per capital rate of increase (b – d); b > d, r = pop increase; d > b, r = pop decrease
Max birth; Min death - rmax—intrinsic rate of increase (constant); low value; different for all species
- ∆N/∆t = rmaxN
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