Flashcards in Natural Selection Model Deck (10)
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1
Fact #1
Potential
exponential increase of
populations
All organisms (even unicellular) have the ability to produce many more offspring than those needed to replace their parents. If all offspring actually survived, the every population would increase exponentially from generation to generation.
2
Fact #2
Steady state of
most populations
In nature, rarely do populations actually increase exponentially for any length of time. While some populations fluctuate dramatically, increases are eventually offset by decreases, and the typical population from generation to generation is pretty close to the long term average (carrying capacity).
3
Fact #3
limitation of resources
The main reason populations do not keep on increasing forever is that they run out of resources. In most environments, the availability of needed resources keeps each population within fairly strict limits.
4
Inference #1
Competition for
resources within
populations
If there are more potential members of a population than can be supported by the resources, then all members will be in competition with all other members to get the resources they need.
5
Fact #4
Individuals vary
within a
population
At least in sexually reproducing populations, every individual is unique, and even in asexual species there is some variation among individuals. (Darwin went to great lengths to show this, because people of the time did not recognize that other organisms were as individual as humans.
6
Inference #2
Differential
survival and
reproduction of
individuals
Some individuals will cope
better with the environmental
limits than others, and will
thus leave behind more offspring than others in the
next generation.
Fitness: ability to produce offsprings. It depend on the environmental pressure (selection is editing by exclusion)
7
Fact #5
Much variation is
heritable
Offspring resemble their parents. As long as the advantages can be inherited, more individuals should have them in the next generation. Inheritance was Darwin's nightmare, as his model was inadequate to allow evolution, but modern genetics has filled that gap.
8
Inference #3
Change (adaptation) of
population over time =
EVOLUTION
If surviving organisms pass on the things that make them better competitors generation after generation, eventually these features will become common in the population. The population will appear better suited for the conditions it faces. The population has adapted.
9
what is adaptation
Adaptation* - A trait that gives an individual an
advantage in its environment OR
the process by which a population acquires
such a trait due to natural selection
10
