Multiple How Affects Populations
1) Genetic Variation.- Mutations: the ultimate source of genetic variation; can be spontaneous or caused by environmental factors like radiation or chemicals.
- Gene Flow: the transfer of alleles between populations; can occur through migration, pollen, or seed dispersal.
- Genetic Drift: the random fluctuation of allele frequencies due to chance events; can occur when a small number of individuals colonize a new area (founder effect) or when a population experiences a bottleneck.
- Non-random Mating: occurs when individuals mate assortatively (i.e., similar phenotypes mate) or disassortatively (i.e., different phenotypes mate). Can alter allele frequencies and lead to evolution
2) Natural Selection.
- Acts on genetic variation, favoring alleles that increase an individual's chance of survival and reproduction in a particular environment.
- Can lead to adaptation: the evolution of traits that make organisms better suited to their environment.
- Different types:
- Stabilizing: favors average phenotypes
- Directional: favors one extreme phenotype
- Disruptive: favors both extreme phenotypes
3) Environmental Factors:
- Abiotic Factors: non-living components of the environment like temperature, precipitation, sunlight, pH, and availability of resources.
- Biotic Factors: living components of the environment like predators, prey, competitors, pathogens, and mutualists.
- Disturbances: events that disrupt an ecosystem; can be natural (e.g., fire, floods, volcanic eruptions) or anthropogenic (e.g., pollution, deforestation).
- Environmental changes can influence population size, structure, and dynamics.
4) Population Size
- Affects genetic variation, as smaller populations are more likely to experience genetic drift and lose genetic diversity.
- Can impact a population's vulnerability to environmental changes and extinction.
- Smaller populations may be less resilient to environmental fluctuations, while larger populations may be more stable and better able to withstand disturbances.
- Affects population dynamics and growth rate.
5) Population Density:
- Number of individuals per unit area or volume; influences interactions among individuals and competition for resources.
- High density can increase competition and transmission of diseases, potentially reducing population growth and survival.
6) Age Structure:
- Refers to the proportion of individuals in different age groups within a population. Important because different age groups have different needs and can contribute differently to population dynamics.
- Can impact population growth, stability, and vulnerability to environmental changes. Populations with skewed age structures may be less resilient and have difficulty recovering from disturbances.
7) Sex Ratio:
- Affects reproductive success and can impact population growth and dynamics.
- Deviations from a balanced sex ratio can alter mating opportunities, competition, and reproductive strategies, potentially affecting the overall population structure.
8) Geographical Range:
- Extent of the area over which a population is distributed.
- Influences genetic variation and adaptation, as different parts of the range may have different environmental conditions.
- Fragmented populations may have reduced genetic diversity and face increased vulnerability to environmental changes.
9) Population Interactions:
- Inter-specific Interactions: interactions between different species, including competition, predation, parasitism, mutualism, and commensalism. Can affect population size, distribution, and dynamics.
- Intra-specific Interactions: interactions between individuals of the same species, including cooperation, competition, territoriality, and kin selection. Can influence social behavior, resource utilization, and population structure.
In summary, multiple factors can affect populations. These factors interact with each other, shaping population characteristics, dynamics, and resilience in response to changing environmental conditions and ecological interactions.