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Population dynamics L5

Population dynamics L5. English in Natural Science 自然科学の英語. Abundance. Birds in river forests (Spain) (Sanchez-Bayo, F. 1985). Abundance vs body size. Small animals are more abundant than large ones Birds are less abundant than mammals. Mammals Log(Y) = 1.3-0.66*log [X] Birds

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Population dynamics L5

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  1. Population dynamicsL5 English in Natural Science 自然科学の英語 自然科学の英語-ENS-L5

  2. Abundance Birds in river forests (Spain) (Sanchez-Bayo, F. 1985) 自然科学の英語-ENS-L5

  3. Abundance vs body size • Small animals are more abundant than large ones • Birds are less abundant than mammals Mammals Log(Y) = 1.3-0.66*log[X] Birds Log(Y) = 0.22-0.54*log[X] 350 mammal and 552 bird species (Silva et al., 1997) 自然科学の英語-ENS-L5

  4. Abundance and distribution Jim Brown (1984) “Population densities decrease towards the boundary of the geographical range of a species” Ilkka Hanski (1982) “Widespread species tend to be more abundant” • Sampling artifact • Specialization Generalist - large area Specialist - small area • Metapopulations and dispersal Western grey kangaroo (Macropus fuliginosus) (Caughley et al. 1987) 自然科学の英語-ENS-L5

  5. Rapoport’s rule (1975) “Geographic range size decreases from polar to equatorial latitudes, with smallest range sizes in the tropics” Why? Tolerance Dispersal favours generalist species Competition + + + Tolerance Dispersal Competition Abundance vs distribution range 523 North American mammals (Pagel et al. 1991) 自然科学の英語-ENS-L5

  6. Big mammals Birds Fish invertebrates Small mammals Population dynamics • Parameters • Natality (fertility) rate • Offspring, reproduction rx = bx ÷ nx • Mortality rate • Life expectancy (longevity) qx = dx ÷ nx • Life tables • Mortality/cohort • Age, sex structure 自然科学の英語-ENS-L5

  7. Exponential Linear Intrinsic capacity for increase r (Lotka, 1925) • Exponential • constant rate (%) Nt = N0 ert N population • Finite rate of increase  = er  individual • Doubling time: time for a quantity to double Dt = 70 ÷r • Linear • constant amount y = x + A • Logistic K = carrying capacity Nt = K ÷ (1+ea-rt) 自然科学の英語-ENS-L5

  8. Exponential growth Populations (human, r = 1.7% year) Food consumption Waste production Economy (Japan: 1-2% year) (USA: 5% year) (China: 7% year) Exponential reduction Radioactive residues Chemical concentration (eg. pesticides, pollutants) Forest destruction 1 2 3 4 5 6 Natural processes Gone! • Linear growth • [CO2] atmosphere • Food production (?) • industry 自然科学の英語-ENS-L5

  9. Reindeer Daphnia rosea (Scheffer, 1951) (Walters et al., 1990) Limits to population growth • Abiotic factors • Temperature • Water availability • Food resource • carrying capacity (K) T.R. Malthus (1766-1834) • Predators 自然科学の英語-ENS-L5

  10. r unrelated to abundance High r (r strategy) Generalist niche Unstable populations Quick recovery Low r (K strategy) Specialist niche Stable populations Prone to extinction Decisive factor: Mortality rate High r Low K How to increase r ? Larger offspring size (r) Increase longevity (K) more times to reproduce Younger reproductive age (both r and K) Repeated reproduction (K strategy) Reproductive success Big-bang reproduction (r strategy) Reproductive effort Life strategies 自然科学の英語-ENS-L5

  11. Stationary distribution No population increase in time Fertility rate = mortality rate r = qx 自然科学の英語-ENS-L5

  12. Competition • Resource competition • Inter or intraspecific • Interference competition (contest) • Usually intraspecific • Sex: males only Resources • Plants • Water • Light • Nutrients in soil • Animals • Food • Space 自然科学の英語-ENS-L5

  13. =r1N1 =r2N2 Competition: Mathematical models Lotka (1925) and Volterra (1926) Species 1 dN1 K1-N1-aN2 dt K1 Species 2 dN2 K2-N2-bN1 dt K2 Species 2 wins Species 1 wins Coexistence Exclusion 自然科学の英語-ENS-L5

  14. Zero growth Neither species can live 1 • Equilibrium point depends on rate of consumption of resources 1 and 2 R1: rate A > rate B A wins 2 Only species A can live 3 Species A wins 4 Species A & B co-exist 5 Species B wins 6 Only species B can live Tilman model (1990) 自然科学の英語-ENS-L5

  15. Spatial segregation Saccharomyces + Schizosaccharomyces yeast (Gause, 1932) outside inside Grain beetles in wheat (Birch,1953) Co-existence • Species must occupy different niches (Gause, 1934) • resource partitioning (share) 自然科学の英語-ENS-L5

  16. Tern species in Christmas Island (Ashmole, 1968) Segregation • Efficient utilization of the same resource • Habitat (space) • Size of prey (diet) • Time • Day - night • Seasons (migration) • Mechanism of evolution • r and K selection theory (MacArthur & Wilson, 1967) 自然科学の英語-ENS-L5

  17. Predators External Big size Parasites Internal - live on host Small size (i.e.larvae) Predation & parasitism • Natural agents to control populations • Exponential increase logistic model • Exponential reproduction ‘biomass waste’ • Producers: plants, phytoplankton • Predation: one species eats another • Herbivores: eat plants • Carnivores/parasites: eat herbivores (prey) • Predators/parasites USE that extra biomass 自然科学の英語-ENS-L5

  18. Abundance Prey (lemming) abundance bird predators Predators and parasites depend on prey/host 自然科学の英語-ENS-L5

  19. Parasitic wasp Prey = Host (Utida, 1957) Models • Discrete populations: one generation/year • Prey Nt+1 = (1-B zt)Nt-C NtPt • Predator Pt+1 = Q NeqPt B = prey reproductive rate C = predator efficiency Q = predator reproductive rate 自然科学の英語-ENS-L5

  20. Predation Intraspecific competition Predator density (P) Environmental pressure (Carrying capacity) Prey population density (N) Caribou (Bergerud 1980; Sinclair 1989) Continuous generations • Lotka (1925) and Volterra (1926): unrealistic • Rosenzweig-MacArthur (1963) Predator equilibrium Food shortage equilibrium 自然科学の英語-ENS-L5

  21. Stochastic variation Humans R0 = 1.1 Stable populations Population regulation Net reproductive rate (R0) = number of female offspring / female / generation Birth rate (b) UP Death rate (d) DOWN • Birth rate (b) DOWN • Death rate (d) UP • predation • disease • food shortage 自然科学の英語-ENS-L5

  22. Probability of extinction (Pielou, 1969) P = (d/b)N0 d = death rate b = birth rate N0 = initial population size b > d P > 1.0 survival b < d P < 1.0 extinction b = d P = 1.0 extinction because of stochastic changes in a lifetime (e.g. disease, climate) Extinction • Species ceases to exist • Causes • Habitat loss • Introduced species (competition, predation) • Overkill • stochasticity • Human impact • Habitat destruction • Overkill (e.g. Dodo, Mammoth, Moa) 自然科学の英語-ENS-L5

  23. Natural extinction • Geological eras and periods • Characterised by changes in biodiversity • Extinction of old forms • Apparition of new forms • Natural causes • Atmospheric composition • Plants increased O2 and decreased CO2 • Astronomic - Milankovitch cycles • Climate variation (i.e. iceage) • Catastrophes (Cuvier, 1769-1832) • Five major extinction events • Cause: asteroids? Earth’s geochemistry? 自然科学の英語-ENS-L5

  24. 15% families 50% genera 52% families 95% species Historical extinction events 自然科学の英語-ENS-L5

  25. Italy Denmark Caribbean Cretaceous-Triasic boundary extraterrestrial iridium layer meteorite (Kastner et al. 1984) (Alvarez et al. 1980, 82) 自然科学の英語-ENS-L5

  26. Mass extinctions…recovery 自然科学の英語-ENS-L5

  27. Evolution and extinction • Extinction is an irreversible process • Extinction events have a founder effect • New taxa appear • Biodiversity flourishes, even more than before • Eventually all species go extinct • Evolve to generate another species (average lifetime of species is 10 m years) • Stop existing - gone! 自然科学の英語-ENS-L5

  28. References • Charles J. Krebs. 2001. Ecology 5th ed. / 応用動物昆虫学 　B-226 • Tokeshi M. 1999. Species coexistence: ecological and evolutionary perspectives/応用動物昆虫学 B-207 • Alvarez, L. W., W. Alvarez, et al. 1980. Extraterrestrial cause for the Cretaceous-Tertiary extinction.Science208: 1095-1108 自然科学の英語-ENS-L5

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