Chapter 10

spatial structure

pattern of density and spacing of individuals in a population

fundamental niche

range of abiotic conditions (temp, humidity, salinity) under which a species can persist

realized niche

range of abiotic and biotic conditions under which a species can persist

geographic range

measure of total area covered by a population (temp and drought define range of sugar maple)

small scale variation in the environment creates _____

geographic ranges that are composed of small patches of suitable habitat

geographic range of fremont’s leather flower is just 3 counties in missouri

• within those counties, plants restricted to dry, rocky soils on limestone outcroppings (limestone glades)

• plants are further restricted by variation in glade soil structure and quality

what are plants limited by

unsuitable environmental conditions

ecological niche modeling

process of determining the suitable habitat conditions for a species

ecological envelope

the range of ecological conditions that are predicted to be suitable for species (differs from realized niche, which describes conditions in which a species currently exists)

when is predicting potential geographic range of species difficult

when only a few individuals exist; researches can use historic distributions of species

chinese bushclover brought to US to control erosion, provide cattle feed, reclaim mined land

• ecologists collected data on envt conditions under which buschclover predicted all locations to which it subsequently spread

  • since bushclover has not spread to all predicted locations, other ecological factors may limit distribution

average temps in north sea have increased 2^o C from 1977-2003

fish species richness increased steadily overtime and positively correlated w/ ocean temp

warmer northern temps caused southern fish species to expand their ranges northward

endemic

species that live in single, often isolated location

cosmopolitan

species with very large geographic ranges that can span several continents

abundance

total number of individuals in a population that exist within a defined area (total number of lizards on a mountain)

what does total abundance of a population provide

measure of whether a population is thriving or on the brink of extinction

what happens when population density is greater than what the habitat can support

some individuals must leave or population will experience lower growth and survival

why are the centers of population geographic range most dense

most amount of resources

near the edges of the range conditions become less ideal

dispersion

spacing of individuals with respect to one another within the geographic range of a population

clustered dispersion

when individuals are aggregated in discrete groups (ie social groups or clustering around resources)

evenly spaced dispersion

when each individual maintains a uniform distance between itself and its neighbors (defended territories, croplands)

random dispersion

when the position of each individual is independent of other individuals, not common due to non-random environmental heterogeneity

difference of dispersal and migration

dispersal is seasonal movement of individuals back and forth between habitats that are more suitable

what does dispersal allow

for species to colonize areas outside of geographic ranges

can be way to avoid areas of high competition or high predation risk

area and volume based surveys

surveys that define the boundaries of an area/volume and then count all of the individuals in the space

size of defined space related to abundance and density of population

what do many samples allow for

determine how many individuals are in an average samplel

line transect surveys

count the number of individuals observed as one moves along a line

how are line transect survey data used

converted into area estimates of a population

counting number of small plants along string tied between 2 fixed points

counting all individuals observed within fixed distance of a line

during the annual christmas bird count, thousands of volunteers follow predetermined path that covers 24km circle and count number of bird species they can see or hear

mark recapture survey

method of population estimation in which researchers capture and mark a subset of a population from an area, return it to the area and capture a second sample after time has passed

how can dispersal be quanitfied

measuring how far individuals travel from a single source location

individuals can be marked and recaptured to determine how far they moved from marking

lifetime dispersal distance

the average distance an individual moves from where it was born to where it reproduces

what does lifetime dispersal distance provide an estimate for

how fast a population can increase its geographic range

what can dispersal cause

a geographic range to expand rapidly if a few individuals can disperse much farther than the average individual

songbird starling populations

existence of few long-dispersal individuals allowed populations to spread 4000km within 60 years

abundance and range

large abundance= large geographic range

caused by resource abilityl

large amount of variation in abundance range size regression may be caused by

fluctuations within a geographic range

suggests that reducing range of population (land to agriculture) will reduce size of population

density and body size

small bodied species live in high densities (mice)

large bodied species live in low density (elephants)

dispersal limitation

absence of a population from suitable habitat b/c of barriers to dispersal

barriers= oceans, deserts etc

most dispersed species dont establish viable populations

how have humans created barriers for dispersal

roads, forest clearings, also assisted in dispersal (bringing over new species)

ex of dispersal caused by humans

aboriginal peoples brought dogs to australia

pine trees have been transplanted all over the world from California

aquatic species are transported in ballast water

habitat corridor

strip of favorable habitat located b/w two large patches of habitat that facilitates dispersal (ie narrow band of trees that connects forests)

cleared plots and central plots dispersal of butterflies

• One plot had a corridor connecting to the central plot; the other plots (“winged” and “rectangular”) were unconnected

  • Researchers tracked dispersal of butterflies from the central plot and found that more individuals dispersed to the connected pot

ideal free distribution

when individuals distribute themselves among different habitats in a way that allows them to have the same per capita benefit; assums perfect knowledge of habitat variation

what does the ideal free distribution allow

populations in low-quality habitats to persist over time

blue tits breed in both downy and oak and holm oak forests

downy oak forests produce 6x as many catepillar prey

downy oak forests support more breeding pairs and pairs produce more offspring

holm oak bird populations would experience an annual decline of 13% if they were not supported by dispersal of offspring from downy oak forests

what happens when individuals frequently disperse among subpopulations

the whole population functions as single structure; all subpopulations inc/dec in abundance synchronously

when dispersal is infrequent ____

each subpopulation fluctuates independently

basic metapopulation model

model that describes scenario in which there are patches of suitable habitat embedded within a matrix of unsuitable habitat; all suitable patches are assumed to be of equal quality

source sink metapopulation model

population model that build upon the basic metapopulation model and accounts for the fact that not all patches of suitable habitat are of equal quality

source subpopulation

in high-quality habitats subpopulations that serve as a source of dispersers within a metapopulation

sink subpopulation

in low quality habitats, subpopulations that rely on outside dispersers to maintain the subpopulaiton within a metapopulation

landscape metapopulation model

population model that considers both differences in the quality of the suitable patches and the quality of the surrounding matrix (habitat corridors)

most realistic and most complex spatial structure of populations