history of life on Earth
began about a billion years after Earth came into existence photosynthesis allowed the oxygen-rich atmosphere that was necessary for the explosion of life, chemical evolution (formation of early crust and atmosphere, small organic molecules in the seas, large organic molecules start forming, first protocells form), biological evolution (single-cell prokaryotes form, single-cell eukaryotes form, led to a variety of multicellular organisms)
biodiversity is facilitated by:
- variable env conditions (Earth’s variability in time and space allowed new and diff landscapes, abiotic and biotic limiting factors and selecting pressures exist (like light, water availability, nutrients, moisture, temps) challenge species)
- genetic variability (differences in tolerances to stress)
- differential survival and reproductive success (speciation, extinction)
- geographic ranges, habitats, and niches (envs present barriers to species from moving from place to place, dispersal, adaptation)
Lamarck’s theory of evolution
proposed evolution by acquired characteristics (learning how to adapt to diff envs)
Darwin and Wallace’s theory of evolution
proposed natural selection as the mechanism of evolution (organisms struggle to survive and reproduce, produce more offspring than can survive, individuals vary genetically, and some fit their env better and survive which creates differential reproductive success and increases gene frequency in the pop)
mutation
accidental and random changes in DNA that may be passed onto subsequent generations, provides a new trait/appearance that can either help it survive or have a lesser change of survival/reproductive success
phenotype
observable expressions of an organism’s genotype, trait associated with the genes
biological evolution
genetic changes in pops of organisms across gens, can be random or direct by selection, can be divergent, convergent, or co-evolution
selection
mechanism by which the frequency of traits change in a pop, non-adaptive traits decrease survival while adaptive ones enhance survival and reproduction, traits are selected as being beneficial or detrimental and, over time, the beneficial ones are inherited and become dominant
specialization
some species have adapted to specific env characteristics since organisms differ in tolerance for variation in limiting factors, stresses over time can be a limiting factor that kills the pop off or force them to adapt
types of selection that causes variability
- directional: one extreme doesn’t work while the other works well, so one species genetically migrates towards the latter trait
- stabilizing: narrows the range of traits to choose the median that provides the most benefit
- disruptive: takes the regular distribution and divides it into diff traits that are beneficial in diff envs, splits the species into two which increases diversity
biodiversity
the number of individual species found within certain envs
speciation
the process of generating new species, a single one can generate multiple new species
types of speciation
- allopatric: results from the physical separation of pops which allows both pops to evolve separately
- sympatric: organisms become reproductively isolated within the same geographic range, two species evolve enough away from e/o to not be able to reproduce together
genetic diversity
individuals in a species vary genetically from one another, provides building blocks for subsequent gens which can change into diff forms, fueled by high pops (low pops result in increasing vulnerability to extinction and genetically similar parents produce less viable offspring)
species diversity
the number of species in a biotic community, varies according to habitats, speciation generates new species and adds to species richness (biodiversity), low biodiversity is likely due to more stresses and limiting factors while high biodiversity is likely due to less stress
extinction
elimination of species and reduction of species richness
causes of extinction
- lack of genetic diversity that produces less viable offspring
- catastrophes
- loss of habitat and food supply
- climate change
- disease
- invasive species and better adaptations create competition for resource
ecosystem diversity
the number and variety of biotic communities within ecosystems, landscape variability and disturbance regimes (disturbances cause the system to change and allows new genetic developments, niches, and habitats) tend to promote higher levels of biodiversity
biogeography
analyzes the concentration of species and similar species in certain areas, biodiversity is unevenly distributed due to env gradients (diff types of and variations in habitats like temp across the globe), species diversity decreases towards the poles and increases towards the equator and tropical regions
key factors in biogeography
- temp gradients: most species are adapted to survive at specific temps, species intolerant to cold temps won’t thrive in cold envs
- altitude: diversity decreases with altitude since the density of air decreases which lessens the amount of O2
- moisture: water is important and critical as a limiting factor, plentiful supply will sustain a high biodiversity while limited supply will only be able to sustain low biodiversity, diversity decreases with dryness
- Light: less available light is not able to sustain a high number of species in comparison to areas with plenty of light
geographic range
spatial extent of a species habitat, limited by physical barriers like oceans, mountains, and other features like moisture and temps
habitat
where a species is able to live within its range, range where a species can survive and be found; oceans
ecological niche
includes biotic interactions and functional roles in biotic communities, related to the specific functions and interactions between a species and its habitat
interactions between species
based on roles and links in food webs, relationships may not always be beneficial and can act as limiting factors, and are integral to the adaptation process
