Mechanisms of Population Change Flashcards
Selective Pressures
organisms over time change as a response to changes in their ecosystem.
Adaptation
variations which assist in the survival of an organism that can be passed on by reproduction to offspring.
Natural Selection
Individuals inherit traits that allow them to survive environmental conditions and then pass this to their offspring. Referred to by Darwin and “survival of the fittest”. These traits are passed on to offspring,
3 broad categories of adaptation
(1) Structural - structure of organism changes
(2) Physiological - body functioning changes; ex. enzymes
(3) Behavioural - nerve control in mammals and hormone control in plants
How can mutations pass on to offspring?
only if they occur to the DNA of gametes.
Selective Advantage
mutations leading this may allow an organism to survive its environment when it otherwise would not have. (Like mutations that lead to the resistance to insecticides)
What is required for species to survive selective pressure?
there must exist variations amongst the species - due to genetic variations which exist or mutations which occur to organisms genes (otherwise a monoculture would never survive)
Artificial selection
when humans choose the traits they want to see in organisms.
For natural selection to occur, there must be…
(1) already existing genetic variations in the species
(2) a selective pressure that causes some to die and some to survive.
(3) reproduction through those that survive in order to pass the genetic variation that gave you the advantage.
Buffon (1707 - 1788)
- noted similarities between humans and apes
- suggested Earth was older than 6000 years
- challenged the idea that life forms are unchanging
Carl Linnaeus (1707 - 1778)
- considered the father of taxonomy
- soley based his divisions on reproductive organs
- developed the binomial nomenclature
Cuvier (1769 - 1832)
- considered the father of paleontology.
- discovered that fossils hidden in sedimentary rock could tell us about the past.
Lyell (1797 - 1875)
- rejected Cuvier’s idea of natural disasters
- theorized that the geologic process actually operated slowly, and that the changes happened over a long period of time
- Inspired Darwin
Lamarck (1744 - 1829)
- observed what her interpreted as the “line of descent”
- believed that offspring inherited traits
- believed that traits could be willed into being
- coined the use/disuse theory
Thomas Malthus (1800’s)
- great influence on Darwin
- said populations would grow exponentially forever, but because of limited resources (food, shelter, etc) the population does not increase because of starvation, disease, etc. and the size reaches a carrying capacity for the given ecosystem.
Wallace (1823 - 1913)
similar ideas to Darwin, but was never published.
Darwin (1809 - 1882)
- accepted that populations changed over time
- discovered “natural selection”
- reasoned that this occured because of competition for limited resources
- that present forms of life have arisen by descent and modification from ancestral species
- survival of the fittest, and that natural selection made species better adapted to their local environments over time
7 Evidences to evolution
(1) Fossil Records
(2) Transitional fossils
(3) patterns of distribution (geological distribution)
(4) comparative anatomy
(5) embryology
(6) molecular biology
(7) genetics
Transitional fossils
fossils which show intermediary links between groups of organisms –> links today’s species to past fossil records
Patterns of Distribution (geological distribution)
the way the continents moved and were once connected, and how climate change affected the changes in plants and animals.
Convergent evolution
over time, similar forms develop in geographically different areas due to similar environments
Divergent evolution
mutations and adaptations to changing environments causes the development of new species from a parent species
Intraspecific competition
competition between the same species
Interspecific competition
competition between different species
homologous structures
can be similar in structure function or both, but come from the same common ancestor
analogous structures
structures in organisms that have similar functions, but came from different ancestors.
Molecular biology vs genetics
molecular biology is the study of molecules, and we can compare them among organisms. Genetics allows us to compare DNA and see the similarities, and also shows us how traits are passed to offspring.
Speciation
the formation of a new species
Transformation
mutations and adaptation to a changing environment over a long period of time results in a new species taking over
Divergence
one or more species arise from a parent species that still exists
For speciation to occur, two population have to be prevented from interbreeding. This can occur in two ways:
(1) geographical barriers
- something that separates two groups of the same species
(2) Biological barriers
- things altering their biology (ex, time of year they reproduce)
Prezygotic Barriers
mechanisms that prevent the fusion of the egg and the sperm so that no zygote can form.
Prezygotic barriers include:
(1) Habitat isolation
(2) Behavioural isolation
(3) Temporal isolation
(4) Mechanical isolation
(5) Gametic isolation
Postzygotic Barriers
mechanisms that prevent a zygote from developing into a fertile adult offspring.
Postzygotic barriers include:
(1) Reduced hybrid variability
(2) Reduced hybrid fertility
(3) Hybrid breakdown
Habitat Isolation
when two closely related species live in entirely different habitats, they will seldom encounter each other and therefore there will be few opportunities to mate
Behavioural Isolation
each species may use different signals to attract a mate. If one species does not recognize that signals of the other, the two species will not mate.
Temporal Isolation
if two species breed at different time of the day or in different seasons, they cannot mix their gametes because when one species is ready to breed, the other is not.
Mechanical Isolation
many species cannot mate because their reproductive anatomies are incompatible
Gametic Isolation
this mechanism is due to the incompatibly of sperm and eggs from different species. The gametes do not fuse because they do not recognize each other.
Reduced Hybrid Viability
genetic incompatibility between the two species may abort the development of the embryo at an early stage
Reduced Hybrid Fertility
if two species can produce hybrid offspring that are viable, reproductive isolation is intact if these offspring are sterile and cannot breed
Hybrid Breakdown
when some species cross mate, the first generation of offspring is viable and fertile. However, when these hybrids mate with each other or with either of the parent species, offspring of the next generation are feeble or sterile.
