Chapter 1 Section 2: Studying Populations
1. Determining Population Size
a. Several ways to measure population sizes
i. Direct observation – Count the population individual by individual (counting all
students in the school)
ii. Indirect observation – Count the evidence of individuals (counting the coats in
lockers in the school)
iii. Sampling – count the individuals in an small area, then multiply that number to
find the total population (count the students in one classroom, then multiply by
the number of classrooms)
iv. Mark-and-Recapture – Capture some individuals and mark them (tags, paint,
etc), release them, come back and capture again. By examining the ratio of
marked to unmarked individuals, and using a mathematical formula, ecologists
can estimate the entire population
2. Changes in Population Size
a. Birth vs Death
i. The main way a population grows is by births
ii. The main way a population shrinks is by deaths
iii. If birth rate is greater than death rate, the population grows. If death rate is
higher than birth rate, the population shrinks
iv. Immigration – individuals moving into a population; results in increased numbers
v. Emigration – individuals leaving a population; results in declining numbers
b. Population Density
i. Population density is the number of individuals per unit area
ii. Ex: 2 monarch butterflies per square meter
3. Limiting Factors
a. Largest population an area can support is called carrying capacity
b. A limiting factor is an aspect of the environment that causes a population to decrease
from carrying capacity
c. Examples are food, water, space, and weather
Chapter 1 Section 3: Interactions Among Living Things
1. Adapting to the Environment
a. Adaptations are characteristics of an organism that allow it to survive and reproduce
b. Natural selection is the process by which the best adapted organisms will survive and
reproduce, thus passing those adaptations on to their offspring
c. Organisms have a variety of adaptations, accumulated through natural selection, that
have made it adapted for its environment and its niche
d. A niche is an organism’s habitat and its job in that habitat (how it gets food, what it eats,
what eats it, etc)
e. Competition
i. When niches overlap, or organisms require the same limiting factor resources,
organisms will compete for those resources. The better an organism can
compete, the more likely it is to survive (better adaptations = better survival
chances)
f. Predation
i. Predation is an interaction in which one organism kills and eats another for food.
ii. Predator is the organism doing the killing, prey is the organism doing the dying
iii. High prey numbers allow predators to increase reproduction, increasing the
population. Increased predator population means more deaths in the prey
population, which limits the food for the predators. More predators starve and
die. Therefore the prey species can increase in numbers again.
iv. Predators and prey both have adaptations that allow them to excel at their roles
1. Predators can sting, run fast, see well in the dark, and use echolocation
(like radar)
2. Prey can use camouflage, false coloring, protective coverings, mimicry,
and warning colors to avoid being killed
g. Symbiosis
i. Symbiosis is a long term interaction between two species in which at least one
species benefits.
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Mutualism
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Parasitism
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Commensalism