Please enable JavaScript.
Coggle requires JavaScript to display documents.
Origins of biodiversity 3.2 - Coggle Diagram
Origins of biodiversity
3.2
Evolution
The cumulative, gradual change in the genetic characteristics of successive generations of a species or race of an organism, ultimately giving rise to species/races different from the common ancestor. Evolution reflects changes in the genetic composition of a population overtime.
Natural selection: An evolutionary driving force - survival of the fittest.
Within a population of a species there is genetic diversity - variation
Populations always over-reproduce but resources are scarce = competition for resources.
Due to natural variation, some individuals will be fitter than others to survive = survival of the fittest
Fitter individuals have an adv and will reproduce more successfully than those who are less fit / don't have the variation.
The offspring of these fitter individuals will inherit the gene that gives the adv. Over time, this will be the dominating new evoluted species and the previous species will decline.
This leads to the formation of new species. Over many generations, the two differences in the species (evoluted and not) become larger. This becomes so significant that if reunited, the species will not be able to interbredd fertile offspring. Thus, the species shave separated and become two spereate species coming form the same common ancestor = biodiversity increases!
Theory of evolution brought by DARWIN. Principles included:
Variation within populations
Overproduction of offspring = high mortality rate - r strategists
Struggle for existence = too many individuals not enough resources
Unequal survival and reproduction rates
Survival of the fittest:
the better adapted will survive more environmental changes than those who don't + will reproduce more leading to an increase in population size.
​Genetic variation
: Caused by mutation (can create new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring). Genetic variation is advantageous to a population because it enables some individuals to adapt to the environment while maintaining the survival of the population.
Speciation
The formation of new species when populations of species become isolated and evolve differently from other populations
.
Isolation
Geographic
= ALLOPATRIC =
The development of a new species as a result of populations being physically separated
. Causes include tectonic plate activity, formation of mountains, lakes, river, deserts etc.
Reproductive
= SYMPATRIC =
New species are formed when there are no physical barriers
Environmental isolation =
Geographic ranges of two species overlap, but their niches differ enough to cause isolation e.g. aquatic and terrestial
Temporal isolation =
Two species whose ranges overlap reproduce at different times.
Gametic isolation =
Sperm and ovaries are incompatible. Fertilisation cannot take place
Behavioural isolation =
Courtship rituals - breeding calls, dances ... - between two species vary / change. There is no more attraction.
Mechanical isolation =
Physical differences e.g. reproductive organs prevent mating or pollination.
The process by which two populations become separated by geographical, behavioural, genetic or reproductive factors. If gene flow between both subpopulations is avoided, new species may evolve
= explained in natural selection
e.g. = Arizona's Grand Canyon formed, squirrels and other small mammals that had once been part of a single population could no longer contact and reproduce with each other across this new geographic barrier. They could no longer interbreed. The squirrel population underwent allopatric speciation. Today, two separate squirrel species inhabit the north and south rims of the canyon. On the other hand, birds and other species that could easily cross this barrier continued to interbreed and were not divided into separate populations
Tectonic plates
The outer crust and upper mantle of the earth (lithosphere) are divided into many plates that move over the molten part of the mantle (the magma) = Tectonic plates.
MOVE APART = CONSTRUCTIVE plate margins
(Magma rises to the surface creating new rock = Mid-Atlantic ridge = sea floor spreading)
Create new island with new habitats + biodiversity
Leads to isolation of populations. Seperates organisms from their common ancestors = divergent evolution (spereate evolution)
The surface of the Earth is divided into tectonic plates, which have moved throughout geological time. This has led to the creation of both physical barriers and land bridges with evolutionary consequences.
MOVE TOGETHER = CONSERVATIVE plate margins
(The San Andreas fault running down the West coast of the USA. Marks the boundary between the Pacific and NA plate.
COLLIDE = DESTRUCTIVE plate margin
(continental plates collide leads to increased plate thickness = mountains OR - the thin dense oceanic crust is sub-ducted under the thick less dense continental curst = ocean trenches, land bridges etc.)- Mountains form physical barriers = isolates populations.
Creates new habitats, promotes biodiversity. Adaptations to these occur through natural selection.
Spread of species through land bridges = a mixing of gene pools and possible hybrids
The movement of the eight major and several minor internally rigid plates of the Earth's lithosphere in relation to each other and the asthenosphere.
Mass extinctions
Period in which at least 75 % of the total number of species on the Earth at the time are wiped out
.
There have been five major mass extinction events in history caused by ABIOTIC factors. We are currently living the sixth major one. It's believed to be accelerated due to growing human population and human hunting / overexploitation BIOTIC FACTORS.
Humans dispersed all over the world around 100 000 years ago.
Humans started to grow food using agriculture around 10 000 yrs ago
Scientists predict that at current rates of extinction, the next mass extinction will take place in about 300 - 2000 yrs.