Ecological levels of organization hierarchy
EcosphereBiomeLandscapeEcosystemCommunityPopulationOrganismOrgan systemOrganTissueCell
Definition of population
Population – group of individuals of a species living together in the same habitat at the same time that mate with one another and produce offspring.• It is isolated from other populations.• There is a barrier to gene flow between populations.• It is not a simple sum of the properties of individuals but creates a new quality.
Features of individual vs features of population
Features of individuals: Features of population- given age -number, density- stage of development -age structure- size -sex ratio- sex => -distribution pattern- has progeny or not -birth and death rates- alive or dead -social behavior, hierarchy in the group- behavior -gene frequencies- fixed genotype
Processes related to individuals and populations
Intra-individual processes: Population processes- development - change of number and (or) density- growth - change of te age strucutre- nutrition => - fecundity- reproduction - mortality- death
Population growth
Nt+1= Nt+B - D + I - E Nt: current populationB: BirthsD:DeathsI:immigrationE:Emmigration
Effective population
The size of the population as estimated by number of its breeding individuals.• Effective population size is lower than the total population size because many individuals do not reproduce due to factors such as inability to find a mate, being too old (postreproductive) or too young (juvenile), poor health, sterility, malnutrition, small body size, and social structure that restrict which individuals can mate.• Many of these factors are initiated or aggravated by habitat degradation and fragmentation.• Because of these factors the effective population size (Ne) of breeding individuals is often substantially smaller than the actual population size (N), what may cause severe loss of genetic variability.• Effective population size may be lowered because of unequal sex ratio, variation in reproductive output, or population fluctuations and bottleneck effect.
Patterns of population distribution
-Clumped-Random-Uniform
Metapopulation
Metapopulation - A network of semi-isolated populations (subpopulations or local populations) with some level of regular or intermittent migration and gene flow among them, in which individual populations may go extinct but their habitats can be then recolonized from other populations. Easier: A population of populations
Features of metapopulations
•Suitable habitat is divided into isolated patches.•Individual subpopulation have realistic chance of experiencing both extinction and recolonization.•The dynamics of the various subpopulations should be largely independent, i.e. not synchronous. It guarantees that as one goes extinct, there are likely to be others generating dispersers promoting the „rescue effect”.•Thus patches may be divided into „sources” (donor patches) and „sinks” (receiver patches).
Definition of patch, corridor and stepping stone
Patch:The fundamental unit of a landscape, containing only one type of habitat. It is a relatively homogeneous area that differs from its surroundings.Corridor:A linear pathway that connects habitat patches and allows organisms to move between them.Stepping stone:Habitat too small to maintain the population for longer, but useful for the migration of animals and dispersal of plants
Demographic variation
Demographic variation (Demographic stochasticity)Random fluctuations in birth and death rates, emigration and immigration, or sex ratio and age structure of a population.• In small populations demographic variation may cause further decline of size leading to extinction.• Species with highly variable birth and death rates, such as annual plants and short-lived insects may be particularly susceptible to population extinction due to demographic variation.• The chance of extinction is also greater in species that have low birth rate, such as elephants, because these species take longer to recover from chance reductions in population size.• When population size drop below a critical number, deviations from an equal sex ratio may occur, leading to a declining birth rate and a further lowering of population size.
Fragmentation of the population
Fragmentation of the population causes they become smaller and smaller. Small populations are subject to rapid decline in numbers and local extinctions for three main reasons:1.Loss of genetic variability and related problems of inbreeding depression and genetic drift.2.Demographic fluctuactions due to random variations of birth and death rates.3.Environmental fluctuactions due to variations in predation, competition, disease, and food supply; and natural catastrophes that occur at irregular intervals, such as fires, storms, or droughts.
Definition of inbreeding and inbreeding depression
Inbreeding:The mating of individuals with close relatives, with whom they may share many genes.Inbreeding depression:A sequence of events initiated by matings between closely related individuals, especially in small populations of normally outbreeding species, whereby heterozygosity and fecundity are reduced and mortality is increased through expression of deleterious, recessive alleles.
Genetic drift
Genetic drift: is the change in the frequency of an existing gene variant (allele) in a population due to random sampling of organisms.
Population bottleneck effect
The drastic reduction in genetic diversity in populations that is a result of environmental catastrophe or excessive human exploitation. Such a population may be limited to a very small number of individuals (often several).
Population viability analysis and minimum viable population
Population viability analysis (PVA)The use of analytical or simulation models to make precise estimates of the likelihood of species persistence within a defined time period at a given level of probability, and to identify and rank or weight threats to such persistence from specific causes.Minimum viable population (MVP)The minimum number of individuals required for a population to persist for a specified length of time at a specified level of probability.
Population restoration efforts typically follow a five-part process:
1.Inventory: a geographically based assessment of rare taxa that documents their existence within mapped political units.2.Survey: an ecologically based assessment of populations in the field that identifies their habitat(s) and endangerment factors.3.Habitat protection: an application of land use restrictions that can be applied, negotiated, or that generate the least political resistance to benefit the endangered population(s).4.Management; deliberate human actions taken to remedy a deficiency or limitation that is causing the population to decline or remain small.5.Monitoring; systematic measurement of population processes over time.6.Recovery; a point at which the population reaches a numerical level, with appropriate demographic patterns, such that extinction by natural catastrophe or environmental, demographic, or genetic stochasticity is no longer likely.
