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Population and communities

Population and communities. Palaeosinecology. Population. Fundamental unit in ecological analysis Population is composed of individuals of a species that lived together.

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Population and communities

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  1. Population and communities Palaeosinecology

  2. 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.

  3. Types of populations • Biocenosis = life assemblage • Fossil population has suffered a variety of post-mortem modification • Lagerstatten deposits are exceptions. • Taphocoenosis = Catastrophic assemblage

  4. 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.

  5. 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

  6. 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]

  7. 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

  8. Type II: suggests constant mortality through the ontogeny . • Type III (blue): simulates a decreasing mortality with age

  9. 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.

  10. Variation in populations • Morphological variations : controlled by ontogenetic, genetic and phenotypic factors • Variation in population size: provoked by physical, chemical and biological changes

  11. 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

  12. J-shaped curve showing exponential growth of a population • This population has not yet reach its carrying capacity. dN/dt= rmax N

  13. Steady growth of population size (same rate of growth within the equaltime 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

  14. 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.

  15. Opportunist and Equilibriumspecies • 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!

  16. Opportunist and Equilibrium species • “K-strategist” or Equilibrium species: long-lived species, low reproductive rates. More facies dependent, moderately abundant in diverse biota.

  17. Factors the determine how much a population will change: growth, stability and mortality

  18. 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.

  19. 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.

  20. 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

  21. 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.

  22. Numericalanalysis of (palaeo)communities • Abundance of specimens are displayed as relativeabundance or relativefrequencydata. Diversitymeasures are standardizedagainstthesamplesize. • Ecologicalindices • Speciesrichness • Abundance

  23. Importance of Speciesrichness 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 .

  24. 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.

  25. Diversity indices • Margalef diversity D= S – 1/log N S = Number of species; N = number of speciemens

  26. Evenness H has the greatest value when each species is with the same specimens numbers

  27. Dominance indices • Berger-Parkerov index= all specimens from sample versus specimens of dominant species d= 0; high dominance d= 1; low dominance

  28. Dominance indices • Simpsonov indeks: S = number of species, ni = number of ith species, N = number of speciemns,: D =decreases as diversity increases

  29. Multivariate techniques • Clusteranalysis: the most appliedmethod • 3 or more saples are compared • Dendograms • Q-mode analysis – is matix of coefficientscalculatedforeachpairofsamples • R-mode analysis – operates on theprobability of mutualoccurrencesofgenera

  30. Markov chain analysis: probabilities of particular transition • Correspondence analysis: matrix of conditional probability • Principal of component analysis: correlation of variance-covariance matrix

  31. Community organization • Trophic structure: the manner in which organisms utilize the food resources

  32. Energy flows through the system through a chain of consumers. Energy loss of 20-30%, rising to as much as 90%, between successive levels.

  33. 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.

  34. 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.

  35. Grazers • Acquire food by scraping plant material from environmental surfaces. • Life site: EPIFAUNAL • Location of collection: Sediment water interface • Food resources: Benthic flora

  36. Browsers • Chew or rasp larger plants • Life site: EPIFAUNAL • Location of collection: Sediment-water interface • Food resources: Benthic flora

  37. 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

  38. 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.

  39. 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

  40. 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.

  41. Suspension-feeding chain

  42. 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

  43. 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

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