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2006 自然科学の英語 -ENS-L5
Population dynamicsL5
English in Natural Science
自然科学の英語
2006 自然科学の英語 -ENS-L5
Abundance
Birds in river forests (Spain)(Sanchez-Bayo, F. 1985)
2006 自然科学の英語 -ENS-L5
Abundance vs body size
• Small animals are more abundant than large ones• Birds are less abundant than mammals
350 mammal and 552 bird species (Silva et al., 1997)
MammalsLog(Y) = 1.3-0.66*log[X]
BirdsLog(Y) = 0.22-0.54*log[X]
2006 自然科学の英語 -ENS-L5
Abundance and distributionJim 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”
1. Sampling artifact2. Specialization
Generalist - large areaSpecialist - small area
3. Metapopulations and dispersal
Western grey kangaroo(Macropus fuliginosus)(Caughley et al. 1987)
2006 自然科学の英語 -ENS-L5
Abundance vs distribution range
Rapoport’s rule (1975)“Geographic range size
decreases from polar to equatorial latitudes, with smallest range sizes in the tropics”
Why?1. Tolerance
2. Dispersal favours generalist species
3. Competition+Dispersal
+ Competition
+Tolerance
523 North American mammals(Pagel et al. 1991)
2006 自然科学の英語 -ENS-L5
Population dynamics• Parameters
– Natality (fertility) rate
• Offspring, reproduction
rx = bx ÷ nx
– Mortality rate• Life expectancy
(longevity)
qx = dx ÷ nx
Big mammals
Birds
Fishinvertebrates
Small mammals
• Life tables– Mortality/cohort– Age, sex structure
2006 自然科学の英語 -ENS-L5
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
Linear
Exponential
• LogisticK = carrying capacity
Nt = K ÷ (1+ ea-rt)
2006 自然科学の英語 -ENS-L5
Natural processesExponential 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
Linear growth– [CO2] atmosphere
– Food production (?)– industry
1
2
3
4
5
6
Gone!
2006 自然科学の英語 -ENS-L5
Limits to population growth• Food resource
– carrying capacity (K)T.R. Malthus (1766-1834)
• Predators
• Abiotic factors– Temperature– Water availability
(Scheffer, 1951)
Reindeer
(Walters et al., 1990)
Daphniarosea
2006 自然科学の英語 -ENS-L5
Life strategiesr 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)
Rep
rodu
ctiv
e su
cces
s
Reproductive effort
Repeated reproduction(K strategy)
Big-bang reproduction(r strategy)
2006 自然科学の英語 -ENS-L5
Stationary distribution
No population increase in timeFertility rate = mortality rate
r = qx
2006 自然科学の英語 -ENS-L5
Competition
• Resource competition– Inter or intraspecific
• Interference competition (contest)– Usually intraspecific– Sex: males only
Resources
• Plants– Water– Light– Nutrients in soil
• Animals– Food– Space
2006 自然科学の英語 -ENS-L5
Competition: Mathematical models
Lotka (1925) and Volterra (1926)
Species 1dN1 K1-N1-N2
dt K1
Species 2dN2 K2-N2-N1
dt K2
=r1N1
=r2N2
Coexistence
Species 1 wins Species 2 wins
Exclusion
2006 自然科学の英語 -ENS-L5
Tilman model (1990)
1
2
3
6
4
Neither species can live
Only species A can live
Species A wins
Species B wins
Only species B can live
5
Species A & B co-exist
Zero growth
• Equilibrium point depends on rate of consumption of resources 1 and 2
R1: rate A > rate B A wins
2006 自然科学の英語 -ENS-L5 Grain beetles in wheat (Birch,1953)
2. Spatial segregation
Co-existence
Saccharomyces + Schizosaccharomyces yeast(Gause, 1932)
inside
outside
Species must occupy different niches (Gause, 1934)1. resource partitioning
(share)
2006 自然科学の英語 -ENS-L5
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)
2006 自然科学の英語 -ENS-L5
Predation & parasitism
• Predators– External– Big size
• Parasites– Internal - live on host– Small size (i.e.larvae)
• 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
2006 自然科学の英語 -ENS-L5
Predators and parasites depend on prey/host
AbundancePrey (lemming)
abundancebird predators
2006 自然科学の英語 -ENS-L5
Models• Discrete populations: one generation/year
– Prey Nt+1 = (1-B zt)Nt-C NtPt
– Predator Pt+1 = Q NeqPt
(Utida, 1957)
Parasitic wasp
Prey = Host
B = prey reproductive rateC = predator efficiencyQ = predator reproductive rate
2006 自然科学の英語 -ENS-L5
Prey population density (N)
Pre
dat
or
den
sity
(P
)
Caribou (Bergerud 1980; Sinclair 1989)
Continuous generations• Lotka (1925) and Volterra (1926): unrealistic• Rosenzweig-MacArthur (1963)
Intraspecificcompetition
En
viron
men
tal pre
ssure
(Carrying capacity)
Predator equilibrium
Food shortage equilibrium
Predation
2006 自然科学の英語 -ENS-L5
Population regulation
Birth rate (b) DOWNDeath rate (d) UPpredationdiseasefood shortage
Birth rate (b) UPDeath rate (d) DOWN
Net reproductive rate (R0) =number of female offspring / female / generation
HumansR0 = 1.1
Stable populations
Stochastic variation
2006 自然科学の英語 -ENS-L5
Probability of extinction (Pielou, 1969)
P = (d/b)N0
d = death rateb = birth rate
N0 = initial population size
1) b > d P > 1.0 survival2) b < d P < 1.0 extinction3) b = d P = 1.0 extinction
Extinction
• Species ceases to exist• Causes
– Habitat loss– Introduced species
(competition, predation)– Overkill– stochasticity
• Human impact– Habitat destruction– Overkill (e.g. Dodo,
Mammoth, Moa)because of stochastic changes
in a lifetime (e.g. disease, climate)
2006 自然科学の英語 -ENS-L5
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?
2006 自然科学の英語 -ENS-L5
Historical extinction events
52% families95% species
15% families50% genera
2006 自然科学の英語 -ENS-L5
extraterrestrial iridium layer meteoriteCretaceous-Triasic boundary
ItalyCaribbean Denmark
(Alvarez et al. 1980, 82) (Kastner et al. 1984)
2006 自然科学の英語 -ENS-L5
Mass extinctions…recovery
2006 自然科学の英語 -ENS-L5
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!
2006 自然科学の英語 -ENS-L5
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. Science 208: 1095-1108