Summary Life Sciences, ISBN: 9781869214470 Life Sciences (Biology)
IEB Life Sciences: Human reproduction
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1. Population and community ecology
Glossary:
All words with ‘*’ can be found below, however, some definitions are found within the
text
Ecology: the study of the interactions of organisms with their physical and biological
environments and how these determine the distribution and makeup populations within
an ecosystem
Biosphere: is the part of the earth where living organisms are found
Ecosystem: is made up of groups of different species of organisms that interact with
each other and with their environment
Organism: an individual form of life, such as bacterium, plant, animals etc., composed
of a single cell or a complex of cells that are capable of growing and reproducing
Community: a group of different species that inhabit and interact in a particular area
Species: is a group of closely related organisms that are very similar to each other and
are usually capable of interbreeding and producing fertile offspring
Individual: single organism capable of independent existence
Population: group of organisms the same species that occupy the same area and can
breed freely with each other
Population size: total number of individuals in a population
Demographics: the statistics such as size, distribution, growth rate etc, of populations
Natality: birth rate in animals or the production of seeds in plants
Mortality: death rate
Immigration: individuals move into a population and stay
Emigration: individuals leave a population and do not return
Environmental resistance: the total number of factors that stop a population from
reproducing at its maximum rate
Carrying capacity: population density that the environment can support
Predation: biological interaction where one species, the predator kills and eats another,
the prey
Aphid: insects that suck the sap of many different plants, including crops
Food web: interconnected set of all the food chains in an ecosystem
Competition: when two or more individuals compete for the same resources that are in
short supply
Specialization: the structural and behavioural adaptations that enable individuals of
different species to coexist
Stratification: many different trees and plants of various sizes and species creating a
vertical structure that divides the vegetation into layers
Eusocial: species that exhibit the highest level of social organization
Age structure: the relative numbers of individuals of each age in a population
Ecological footprint: measure of human demand on the earth’s ecosystem
, 1. Population ecology
Is concerned with fluctuations in the size of a population and the factors, both
physical and social that regulates these fluctuations
Factors that affect the size of a population:
● Natality*
● Mortality*
● Immigration*
● Emigration*
For humans the:
● Birth rate = number of births per 1 000 people per year
● Death rate = number of deaths per 1 000 people per year
Populations will therefore:
● Grow when birth and immigration exceed death am emigration
● Decline when death and emigration exceed birth and immigration
● Remain stable when birth and immigration approximately equal death and
emigration
In a closed population, with no immigration or emigration, the only parameters
affecting any change in population numbers will be births or deaths
Population growth regulation: if a few individuals enter an unoccupied area where
there is no shortage of food/resources and no predators will reproduce and the number
of individuals increases exponentially
● As numbers increase, more demands are made on resources and builds up
environmental resistance* which causes birth rate/immigration rate to decrease
and the death rate/emigration rate to increase
● Eventually, balance is restored and population stabilizes at a particular
size/number, this number is called the carrying capacity* of the ecosystem
● The population fluctuates around the carrying capacity until the environment
changes again
● Population size fluctuates seasonally and annually depending on the
resources available
● Population size in an ecosystem is self-regulating
● All negative-feedback mechanisms and examples of this self-regulation
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