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 reproduction2. frequence of reproduction3. number of offspring produced4. reproductive life span5. 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 logisticdN/dt=[rN][K-N/K]dN= changes in population sizedt= unit of timeN= actual population sizeK= Upper limit of population sizer= 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 indices1.Species richness2.Abundance

Importance of Species richness and abundances

1. Productivity of the environments2. Relationship between stability of

ecosystem and species richness3. 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 NS = 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 dominanced= 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

• 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

meio- and 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 suspension-feeders (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

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Odgovor vježbe 1

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