Transcript Population and communities

Population and communities
Palaeosinecology
Population
• Fundamental unit in ecological analysis
• Population is composed of individuals of
a species that lived together.
• Spatial distribution , age structure and
abundance of individuals of a species
are governed by differences is the way
organisms utilize energy resources.
Types of populations
• Biocenosis = life assemblage
• Fossil population has suffered a variety
of post-mortem modification
• Lagerstatten deposits are exceptions.
• Taphocoenosis =
Catastrophic assemblage
Size frequency analysis
• Class interval are chosen for size groups
and a frequency table is constructed for
all the size intervals.
• Presentation: histograms or cumulative
frequency polygons or polygons
• 3 types of frequency histograms are.
• Positively-skewed curve: high infat
mortality (most invertebrates)
• Normal, Gaussian curve: high mortality
in the mid/late life group
• Negatively skewed curve: high senile
mortality
• Unimodal or multimodal-peak
distribution
Age of fossil specimens
• The absolute age of fossil specimens is
difficult to define
• There is relationship between size and
age :
D (size) = S (constant) * [T(time) + 1]
Deceleration with age in many taxa:
D(size) = S (constant) * ln[T(time) +1]
Survivorship curves
• The curve plots the number of survivors
in the population at each growth stage
or defined age.
• The individuals of the same age form
COHORT.
• 3 types of curves
• Type I (in red) : depicts an increasing
mortality with age
• Type II: suggests constant mortality
through the ontogeny .
• Type III (blue): simulates a decreasing
mortality with age
• Type I: indicates a more favourable
conditions throughout ontogeny!
• Survivorship curves give us information
on maximum age of a population, its
growth and mortality rates.
Variation in populations
• Morphological variations : controlled by
ontogenetic, genetic and phenotypic
factors
• Variation in population size: provoked by
physical, chemical and biological changes
Changes in population size
• Biotic potenstial: maximum rate at
which a population could grow under
given optimal condition. Factors are:
1. age of reproduction
2. frequence of reproduction
3. number of offspring produced
4. reproductive life span
5. average death rate under ideal
conditions
• J-shaped curve showing exponential
growth of a population
• This population has not yet reach its
carrying capacity.
dN/dt= rmax N
Steady growth of population size (same rate
of growth within the equal time period)
• Population can grow logistic
dN/dt=[rN][K-N/K]
dN= changes in population size
dt= unit of time
N= actual population size
K= Upper limit of population size
r= intrinsic rate of increase
Spatial distribution
• Regular: space between individuals are
developed by competition or by efficient
exploitation of resources. Nomarine
environments.
• Random: individuals in a population are
located independently from all other
members of the population. No overall
biological or environmental control
• Clumped: common in marine and nomarine
environments.
Opportunist and Equilibrium
species
• Correlation between life style, habitat
and the life history of an organism:
• “r-strategist” or opportunists: matured
early, produced small but numerous
offspring, died young! Usually abundant,
widespread, cosmopolite, dominating a
variety of facies and biotic association!
Opportunist and Equilibrium
species
• “K-strategist” or Equilibrium species:
long-lived species, low reproductive
rates. More facies dependent,
moderately abundant in diverse biota.
• Factors the determine how much a
population will change: growth, stability
and mortality
Community
• Association of species of particular
habitat.
• The are organized according to the way
the organisms obtain their food and in
their competition for a space.
Community structure
 Open community: populations of
different density and spatial
distribution. Each population has a low
specimens abundance.
 Closed population: populations of equal
densities and spatial distribution. Sharp
borders are.
Palaeocommunities
• Fossilized residues of living communities
• Characterized by species composition
and the relative abundance of
individuals
• Palaeocommunity has to be in situ
• Assemblage versus Association
• Rigorous sampling methods: line
transects, bedding plane counts and
standardize bulk samples
Numerical analysis of
(palaeo)communities
• Fossil community is rarely complete and
in place
• General trend in communities:
Inverse relationship between size and
abundance
In order of decreasing size, the
megafauna, meiofauna and microfauna
are more abundant.
Numerical analysis of
(palaeo)communities
• Abundance of specimens are displayed
as relative abundance or relative
frequency data. Diversity measures are
standardized against the sample size.
• Ecological indices
1. Species richness
2. Abundance
Importance of Species richness
and abundances
1. Productivity of the environments
2. Relationship between stability of
ecosystem and species richness
3. Ecosystem with high species richness do
not allow entrance of “foreign” species.
4. High diversified community does not
change considerable by illness.
5. If the number of specimens drop for 75%
that means that diversity is reduced .
Diversity indices
• Shannon-Wienerov indeks:
pi = relative frequency of ith species; S number of
species.
Greater number of species within community pi
shows lower value, and index gets higher value.
Diversity indices
• Margalef diversity
D= S – 1/log N
S = Number of species; N = number of
speciemens
Evenness
H has the greatest value when each
species is with the same specimens
numbers
Dominance indices
• Berger-Parkerov index= all specimens
from sample versus specimens of
dominant species
d= 0; high dominance
d= 1; low dominance
Dominance indices
• Simpsonov indeks:
S = number of species, ni = number of ith species, N =
number of speciemns,:
D =decreases as diversity increases
Multivariate techniques
Cluster analysis: the most applied method
3 or more saples are compared
Dendograms
Q-mode analysis – is matix of coefficients
calculated for each pair of samples
• R-mode analysis – operates on the
probability of mutual occurrences of
genera
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• Markov chain analysis: probabilities of
particular transition
• Correspondence analysis: matrix of
conditional probability
• Principal of component analysis:
correlation of variance-covariance
matrix
Community organization
• Trophic structure: the manner in which
organisms utilize the food resources
• Energy flows through the system
through a chain of consumers. Energy
loss of 20-30%, rising to as much as
90%, between successive levels.
Suspension-feeders
• Remove food from suspension in the water
mass without need to subdue or dismember
particles.
• Life site: EPIFAUNAL, INFAUNAL
• Location of collection: water mass (high or
low)
• Food resources: Swimming and floating
organisms, dissolved and colloidal organic
molecules, some organic detritus.
Deposit-feeders
• Remove food from sediment either
selectively or non-selectively. Without
need to subdue or dismember particles.
• Life site: EPIFAUNAL, INFAUNAL
• Location of collection: Sediment water
interface, in sediment shallow to deep
burrows
• Food resources: Particulate organic
detritus, living and dead smaller members
of benthic flora and fauna and organic rich
grains.
Grazers
• Acquire food by scraping plant material
from environmental surfaces.
• Life site: EPIFAUNAL
• Location of collection: Sediment water
interface
• Food resources: Benthic flora
Browsers
• Chew or rasp larger plants
• Life site: EPIFAUNAL
• Location of collection: Sediment-water
interface
• Food resources: Benthic flora
Carnivores
• Capture live prey
• Life position: EPIFAUNAL; INFAUNAL;
NEKTO-BENTHIC
• Location of collection: Sediment-water
interface and in sediment
• Food resources: Benthic epifaunal meioand macro fauna and benthic infaunal
meio- and macro fauna
Scavengers
• Eat larger particles of dead organisms
• Life site: EPIFAUNAL, INFAUNAL
• Location of collection: Sediment-water
interface and in sediment
• Food resources: dead, partially decayed
organisms.
Parasites
• Fluids or tissue of host provide
nutrition
• Life site: SAME AS HOST
• Location of collection: same as host
• Food resources: mostly fluids and soft
tissue
Food chains
• Different length and the dominance of
participating trophic groups
• GRAZING - BROWSING food chain:
primary producers are benthic algal
mats, seaweeds and angiosperms.
Grazers and browers are gastropods,
other molluscs and herbivorous fishes.
Predators are fishes.
Suspension-feeding chain
• Primary producers are phytoplankton,
which are consumed by zooplankton, and
then this mixture of phytoplankton and
zooplankton plus organic detritus is
consumed by variety of suspensionfeeders (brachiopods, bivalves,
bryozoans, sponges, corals and crinoids).
predators
Detritus-feeding food chains
• Large amount of organic detritus
(muddy environments like tidal flats and
lakes). Deposit-feeders are polychaete
worms, bivalves with labial palps,
gastropods, starfish and trilobites.
Predators
• Greater productivity  greater food
resources  greater species richness
• Greater productivity  food richness 
specialization of organisms  narrow
niches
• Greater productivity  more energy in
the base of food chain  greater length
of the chain  more species
• Space’s diversification  more species
• Complex community structure  more
microhabitats  more species
• Stable environment  more species
• “Favourable” environment  more
species
• Greater competition  more species
• Long-term evolution  more species
Community succession
• Community change through time within
unchanging environments.
• It should be distinguished from
ecological replacement, in which faunas
succeed one another as a response to
changes in environment.
• Succession begins with a PIONEER
stage and progresses through MATURE
stage to a CLIMAX stage.
• The entire sequence of stages is named
SERE.
• Pioneer species are opportunists,
generalists, r-strategists, high
fecundity and rapid growth rates,
eurytopic and cosmopolitan. They are:
crinoids, bryozoans, algae and branching
corals
• Climax species: specialists, narrow
niches, low fencundity and low growth
rates, long life histories
• Changes in community structure:
Global climate changes – regional to
continental migration and, local to
regional extinction.
Mass extinction – geologic extinction
and evolutionary recoveries
Vježba 1
• Organiziraj hranidbeni lanac među
zadanim organizmima: dijatomeje, ljudi,
ostrakodi, tuna i inćun, tako da
razlikujete primarne proizvođače,
primarne potrošače…
Odgovor vježbe 1
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Proizvođač: dijatomeja
Biljojed: ostrakod
Primarni mesojed: inćun
Sekundarni mesojed: tuna
Tercijarni mesojed: čovjek