Ricklefs 6th Ed Ch 10 Notes

Ricklefs 6th ed. CH 10: The Distribution and Spatial Structure of Populations (p.198-219):
-primary threat to populations of many species is the fragmentation of their habitat
-Organisms can use a particular habitat path only if they can gain access to it by moving through less favorable surrounding habitats
-Fragmentation reduces habitat quality
population = individuals of a species within a given area; ha integrity as a unit of organization-reproduce
subpopulations (local populations) = small divisions in which individuals move less frequently
distribution (population extent) = geographic area occupied by a population (geographic range)
population structure = number of attributed, including density and spacing of individuals within a suitable habitat and the propitiations of individuals of each sex and age class (ex. Spatial structure)

Populations are Limited to Ecologically Suitable Habitats:
Fundamental niche = range of physical conditions over which a species can persist
Realized niche = conditions, predator, pathogens, competition which further limit distribution
Dispersal limit = absence of a population from suitable habitat because of barriers to dispersal (increased by human actions)
-many animals, particularly those that fly or swim, undertake extensive migrations
-some as a response to occasional failure or depletion of local food supplies (ex. Irruptions)

Ecological Niche Modeling Predicts the Distributions of Species:
The more suitable the conditions for a species, the denser its population, and the greater its productivity
Ecological niche modeling = mapping occurrences of a species in geographic space, then catalog the combination of ecological conditions at the locations where the species has been recorded
Ecological envelope = catalog of ecological conditions for a species (ex. Invasive species)
The world is constantly changing, and sometimes species have difficulty moving with shifting geographic areas of suitable conditions (major concern given current global warming)

The Dispersion of Individuals Reflects Habitat Heterogeneity and Social Interactions:
Dispersion = spacing of individuals with respect to one another within the geographic range of a population. Ranges:
-Clumped = individuals found in discrete groups
-Random = completely uniform enviro, distributed w/out regard to others in population (RARE)
- Spaced = individual maintains a minimum distance between itself and its neighbors

The Spatial Structure of Populations Parallels Environmental Variation:
Density = number of individuals per unit of area
Species tend to be most numerous in the center of its range and to decrease in density toward periphery (pattern highly irregular due to non-uniform environmental conditions)
Ideal free distribution = individuals move from better to poorer patches until each path has the same value for individual fitness, regardless of intrinsic patch quality
Individuals rarely have perfect knowledge of patch quality and dominant (those with higher reproductive success) individuals may force subordinated to leave high-quality patches
Local adaption at the periphery of a species range is prevented by immigration of dispersing individuals from the center of the range, which brings genomes adapted to the conditions in the optimal habitat for the species

Three Types of Models Describe the Spatial Structure of Populations:
Metapopulation Models = describe set of subpopulations occupying patches of a particular habitat type between which individuals move occasionally (habitat matrix)
Source-Sink Model = add differences in the quality of suitable habitat patches
Source populations = individuals produce more offspring then required to replace themselves in areas where resources are abundant
Sink populations = populations maintained by immigrations of individuals from elsewhere because too few offspring are produced locally, in areas of poorer habitats
Landscape Model = considering the effects of differences in habitat quality within habitat matrix (most complex)

Dispersal is Essential to the Integration of Populations:
Measuring dispersal, particularly over long distances, requires marking and recapturing individuals
Lifetime dispersal distance = indicated on average how far individuals move from their birthplace to where the reproduce
Neighborhood size = number of those individuals estimated by the lifetime dispersal area and population density
Average dispersal distance bears a constant relationship with population density across many species

Macro ecology Addresses Patterns of Range Size and Population Density:
Macroecology = analyzing and interpreting patterns of shape distribution and population size
Geographic range and population density in the center of the distribution should be positively correlated
Often observe patterns of species presence and absence that vary over time, and closely related species can have very different ranges
Population density decreases with increasing body size (matter of relative size to space, metabolic rate)
Energy equivalence rule = populations tend to consume the same amount of food per unit of are regardless of size of the individuals
Variation if population density or overall population size in response to changes in climate, resources, or predators and pathogens is often mirrored by changes in distribution, particularly in small organisms with short life spans.

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