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