Part B:A biological and ecological basis for monitoring
Chapter 4 Elements of Ecology and Ecological Methods
Population Size
Changes in size are partly due to
externma factors and partly due to inherent population characteristics.
pg. 64 "This lack of detailed and
continuous data from long-term population studies poses not insignificant
problems in monitoring because, in the face of a multifactorial source
of variability it is difficult to distinguish trends to to pollution from
those which are inherent long-term cycles."
Population distribution and limits of tolerance
organisms with narrow tolerances
(or species taht are sensitive to small changes in their environment)
may be useful indicator species because changes in distribution and abundance
in these species may indicate environmental perturbations like chemical
pollution
Distribution Patterns
spacial distribution can theoretically
be either uniform, random or aggregated - meaning most often found sigma^2
> x bar
Population Structure
age-class distributions of
size-class distributions provide a summary of the populations status and
so give a useful basis for monitoring changes in populations, mean life
expectancy can be calculated
Communities and Ecosystems
ecological community: assemblage
of interacting populatiosn of different species ina particular area
or habitat
ecosystem: consists of the ecological
community and the abiotic environment with which it interacts in a dynamic
and complex way
study ecosystems via nutrient cycle
and energy flow
Niche and Resource Partitioning
biotic factors as well as abiotic
factors are important in determinng species composition and community structure
way to look at species interactions:
examine how
different resources such as food, space or roosting sites, etc. are divided
or partitioned between different species
first we look at the niche of each species
niche - defined as the sum of all the relationships between the species
and the environment
can alternatively be defined as teh activity range of each species along
every dimension of the abiotic and biotic environment
in isolation plants and animals are
able to exist in a wide range of environmental conditions and that range
of conditions defines it's fundamental niche
outside the fundamental niche, the
plant or animal will not survive
in natural communties a species has
a realized nice, that is in the presence of competition and predators,
not all resources may be used to the extent at which it would be, if the
species were in isolation - the extent to which resources are used in this
situation is called the 'realized niche'
Some formulas to describe this:
B(Breadth
of niche) = 1/[(sum from i=1 to s) (P sub i) ^2] -> simpler in formula
form
Where P sub
i is the frequency of utilization of each category
Ex. A lizard's diet consists of 10% lizards, 40% ants and 50% spiders.
Using this information plug in for P sub i : .1, .4 then .5 - after squaring
each, taking the inverse and summing, you end up with a measure of the
breadth of the niche of
species of lizard.
When species
interact you can calculate the niche overlap, or how much of the resources
are needed by both:
O sub j,k
(Overlap) = [(sum from i=1 to s) P sub ij * P sub ik]/[square root of ((sum
from i=1 to s P sub ij ^2)*(sum from i=1 to s Psubik ^2))]
-> a lot simpler in formula form
Abundance and Rarity
natural and unnatrual rarity
exist
commonness and rareness of a species
is an important and interesting phenomenon which is basic to our understanding
of the use of species richness, species diversity and other variables used
in monitoring
Ecological Succession
development of a community over time,
or the process of change is called ecological succession
although succession is a process of
continual change, it can be described as a series of phases (seral stages)
through which the community develops
succession can be viewed as the development
of a community from it's inception (pioneer stage) which is then replaced
by a whole series of communities
whole sequence is called a sere and
each stage can be considered a community in its own right
final, mature community is called
the climax community
in general, species richness increases
as the climax community is approached
primary succession -> establishment
and development of communities in newly formed habitats
secondary succession -> recolonizations
where natural communties have been destroyed
terrestial habitats -> climax stage
usually dominated by long-lived plants
process of natural change may be arrested
by man's activites such as by burning or cutting
ex. Europe's heathlands are
managed communities where the natural change to woodland has been arrested
resulting in a plagioclimax community
Chapter 5 Ecological Methods
Qualitative and Quantitative Surveys
what species are there? where
are they? how many are there? finding out what species are
present in order to build a picture of species composition requires less
rigorous sampling than does estimating species abundance
to find out which species are present
a useful method is to keep a cumulative record of the number of species
recorded (along transects or in quadrants)
eventually the probability fo finding
a new species will diminish, which indicates a thorough sample has been
made
random stratified sampling is the
most common type used
sampling is divided on the basis of
a subjective classification, and the plots are randomized
number of sample replicates are required,
and statistical analysis of these replicates gives some amount of precision
Frequency of Sampling and Location of Sampling
monitoring requires that information
is collected at intervals throughout time and the frequency of data collection
is cruicial to success
ex. sampling frequency can be twice
the highest frequency of the event being monitored
for thorough sampling of an area random
selection of location is necessary, but for consistant data within an area
constancy of location in necessary
Population Size
when counting individuals, or finding
an estimate of population size is hard, the population index is used:
regular census
of small sample populations
changes in
the index may reflect changes in the total population
capture-recapture method is a popular
what to estimate the size of a population
# of marked
in sample/total caught in sample = # marked in
population/total population size
alternatively
written as P = an/r
where:
P is the population size
a is the total number of animals marked
n is the number of individuals caught again (marked) in a subsequent sample
and
r is the total caught in the sample
Species Associations
species composition, relative abundance,
dominance and species associations are all important characteristics
size of sampling quadrants has a great
impact on the data recorded