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39 Cards in this Set
- Front
- Back
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Basic link of genetics to conservation
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Small, isolated populations tend to lose genetic variation over time through slow erosive processes and faster deleterious effects of inbreeding
Provides an overview of the principles of molecular and population genetics, and how the theory can provide understanding of biological systems |
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Species pool of genetic diversity exists at 3 levels:
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1) Genetic diversity within individuals
2) Genetic diversity among individuals within a population 3) Genetic differences among populations |
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Neutral and Adaptive variation:
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Genetic material that does not appear to code for anything – neutral genetic variation
Genes under selection – Adaptive variation |
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Variation within and among individuals:
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Variation within individuals produced each generation during recombination during sexual reproduction. (Any gene locus has 2 alleles inherited from 2 parents)
At a population level, a locus can be monomorphic or polymorphic At the individual level, a polymorphic locus can be homozygous (same allele) or heterozygous (different alleles) Overall level of heterozygosity is the measure of genetic variation within individuals |
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Value of measuring genetic variation within individuals:
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Heritable variation is the basis for evolutionary change
Inbreeding occurs at the individual level Knowledge of individual genotypes necessary for captive breeding programs Genetic variation is always measured at the individual level |
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Genetic model for among population diversity:
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HT = HP + DPT
HT = total genetic variation (heterozygosity) HP = average diversity within populations DPT = average divergence among populations surveyed |
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Genetically Effective Population Size (Ne)
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Defined as the size of an idealized population that will result in the same amount of loss of heterozygosity or change in allele frequencies as in the actual population being considered.
Lower heterozygosity in populations with unequal sex ratios, fluctuating population sizes, and non-random reproductive success of individuals |
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Mutations:
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Mutations is a major source of genetic variation
Mutations occur when DNA is altered in such a way as to change genetic message – error in replication of nucleotide sequence Mutations can be neutral or alter gene expression Probability of fixation of deleterious gene more likely in small populations Mutational meltdown – accumulation of deleterious mutations with an increased probability of fixation of future mutations |
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Genetic Drift
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Random fluctuations in gene frequency over time due to chance alone
Drift leads to loss of variation more quickly, and is thus of greater conservation concern in small populations |
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Gene flow
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Movement of genes from one population to another
While genetic drift tends to create differences in separate populations, gene flow will reduce differences Measuring gene flow is difficult Genetic data are used to estimate number of migrants received in a population per generation (m) If product of effective population size and migration rate (Nem) is greater than 1 (one migrant per generation), rate of gene flow sufficient to minimize loss of heterzygosity |
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Inbreeding depression
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Inbreeding - Mating between close relatives
Probability of occurrence greater in small populations even if mating is random Increases frequency of homozygous genotypes Inbreeding depression – decreased fitness resulting from inbreeding |
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Outbreeding depression:
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Decreased fitness resulting from “genetic swamping” of adaptive genes
Decreased fitness resulting from the breaking down of physiological or biochemical compatibilities that evolved in different populations |
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Natural Selection
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Differential survival and reproduction of different genotypes (or differential success of genotypes)
Different forms of selection – - Viable selection: differential survivorship to adulthood - Sexual selection: differential mating success - Fertility selection: differential production of offspring |
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Parentage and systems of mating:
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Polygymy
Polyandry Use to distinguish social mating systems and genetic mating systems |
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Directional Selection and Fitness:
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If fitness of homozygous genotype is greater, over time, fitness of one allele gradually decreases to 0
In situations of overdominance or heterozygous superiority, both alleles will be maintained in the population |
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Three time scales for genetic conservation:
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Maintenance of viable populations in the short term – avoid extinction
Maintenance of the ability to continue adaptive evolutionary change Maintenance of the capacity for continued speciation |
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Two criteria for inclusion as Evolutionary Significant Units under the Endangered Species Act:
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Groups must be substantially reproductively isolated
Groups must represent a important evolutionary legacy – this criteria is met if the population is contributing to ecological or evolutionary diversity |
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Use of pedigrees
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Pedigree analysis – represents genetic study of a multigenerational population with ancestral linkages that are known or can be modeled
Use typically restricted to small captive populations “Genetically important individuals” |
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Principles to maintaining in pedigree analysis:
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Maintenance of large effective population sizes
Equalizing number and sex ratio of breeders Decreasing variance of reproductive success of breeding individuals Reducing fluctuations in population size over time |
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Estimating degree of relatedness without pedigree information:
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Numerous relatedness estimators
One estimator uses population allele frequency and number of alleles shared For randomly mating populations, average level of relatedness is 0 Parents and offspring, and full siblings share half of all alleles, relatedness is 0.5 Example - Flightless bird Guam Rail |
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Limitations of the use of Genetics in Conservation:
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“Genetic factors do not figure among 4 major causes of extinction – overkill; habitat destruction and fragmentation; impact of introduced species; and secondary or cascade effects” - Woodruff, 1992
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BIDE factors:
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Population size driven by Birth, Immigration, Death, Emigration
Changes in population can be tracked using principles and techniques of population demography – age-dependent birth and death rates Secondary demographic factors (also called life-history characteristics) play role in long-term population trends |
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Population regulation via density dependent and density independent factors:
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Howard and Fiske (1911) distinguished “catastrophic mortality factors” – factors that kill a constant proportion of the population independent of density and “facultative mortality factors” – factors that kill increased proportions of the population as density increases
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Mechanisms of population regulation:
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Increased mortality or decreased natality due to shortage of resources
Increased mortality due to increased predation, parasitism or disease Increased mortality or decreased natality due to increased intensity of inter and intraspecific social interactions |
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Problems specific to very small populations:
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Genetic loss – more relevant to small populations
Demographic variability and decline - more relevant to small populations Environmental variation – can harm both small and large populations Catastrophes – can harm both small and large populations |
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Population Viability Analysis (PVA):
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Examines demographic effects of different threats or management practices on a population (or set of populations) by projecting into the future
Quantitative risk assessment Combines demographic parameters with simulation modeling Can be used to determine when a population becomes too small to fulfill ecological role |
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Ecologically Functional Populations
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Small population size could result in loss of ecosystem function
PVA can be used to understand when species drops below its “Ecologically Functional Population Size” |
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Importance of Ecologically Functional Population size:
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Ensures ecosystem health
Ecologically Functional Population size larger than Minimum Viable Population size, therefore requires larger area for persistence. This makes it more effective in ecosystem conservation Rich interactions that define natural communities are worthy of protection |
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Information required to make population projections:
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Starting population size
Habitat type occupied by species Characteristic birth and death rates in that habitat type |
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Hierarchical models can predict future so long as:
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Habitat specific birth and death rates remain unchanged
The fraction of population in each habitat does not change |
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Three major elements of Spatially Explicit Population Models (SEPM):
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Landscape maps
Scenario of how landscape will change Population dynamics simulations |
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Conservation efforts at sea: 3 primary boundaries recognized:
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Continental shelves
Exclusive economic zones Open ocean |
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Contributions of the model to understanding of the extinction risk in Neotropical migrants:
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Demonstrates how demography interacts with components of landscape change
Providing an integrated assessment of landscapes as population sources or sinks Highlights importance of historic effects such as different trajectories of landscape change Emphasizes potential for lagged population responses Illustrates potential for demographic limitations to population recovery |
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Ecological Restoration
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The process of intentionally altering a site to establish a defined, indigenous, historic ecosystem
The goal of the process is to emulate the structure, function, diversity and dynamics of the specified ecosystem |
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The process of Ecological Restoration includes:
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Examining preexisting, historic and current reference conditions prior to designing the restoration plan
Developing a restoration design or plan Obtaining the necessary permits to perform the work Implementing the design including soil modifications, hydrology, and plant and animal communities Monitoring of restored site |
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Green Belt Movement
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Started in Kenya in 1977 by Wangari Maathai
Established the link between poverty and deforestation Program involves planting trees through community action Program now spread to other countries in East and Central Africa |
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Animal Relocation
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Usually undertaken for species that are highly endangered
Includes ex situ breeding Reintroduction Translocation |
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Steps in designing and implementing ecological restoration:
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Site Assessment
Setting goals Design Implementation Monitoring and adaptive management |
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Environmental regulations driving restoration practices:
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Clean Water Act (1972)
Endangered Species Act (1973) Surface Mining Control and Reclamation Act (1977) International regulations (reclamations of degraded mining lands; Convention on Biological Diversity) |
