Conservation of Populations

1
Conservation of Populations

• Defining Populations
• Demographics growth and decline
• Conservation genetics populations

2
I. Defining populations

• Spatial disjunction
• Distribution pattern, groups are separated by
  location, regardless of other similarities
• Genetic disjunction
• All individuals in one group share genetic
  attributes with one another, but not with
  individuals from other groups
• Demographic disjunction
• Individuals from different groups have different
  demographic properties birth rate, death rate,
  sex ratio, age structure

3
Important characteristics of a population

• Population Density number of individuals per
  unit area or volume
• Sampling to estimate density
• Absolute Density
• Capture-Recapture Method
• Quadrant techniques

4
(No Transcript)
5
Dispersion pattern of spacing among individuals

• Limited by abiotic factors
• Patchy environment will affect dispersion within
  population
• Limited by biotic factors, species interactions

• Abiotic factors
• Biotic Factors

6
DISPERSION PATTERNS Clumped pattern
individuals aggregated in patches Uniform pattern
evenly spaced resulting from direct
interactions Random pattern occurs in the
absence of strong attractions or repulsions among
individuals
7
II. Demographics growth and decline

• Recruitment, fecundity
• Immigration
• Emigration
• Death
• survivorship
• Natality (avg. per capita birth rate)
• Mortality (avg. per capita death rate)

8
Density dependent fecundity in fingernail clams,
Musculium securis
9
B. Life histories and population size

• Traits that affect an organisms schedule of
  reproduction and survival
• Semelparity reproduction
• iteroparity reproduction
• Limited resources and trade offs
• Red deer in Scotland
• Insect species
• Perennial plants

10
Different life histories represent a resolution
of conflicting demands. When an organism
engages in one activity other activities are
constrained!
time energy nutrients
limited resources
11
Population Growth Models

• increases if birth rate gt death rate
• Exponential
• unrestricted growth due to abundance of resources
  (food/space)
• the larger the population, the faster its
  potential for growth.
• ?N rmaxN
• ?t
• Logistic
• ?N rmaxN (K N)
• ?t K

12
C. Population growth factors

• Density Dependent
• Negative feedback
• Density Independent
• Top-down effects
• Bottom up effects
• Indirect effects

13
III. Conservation Genetics

1. What is Genetic Diversity?
2. Why is Genetic Diversity Important?
3. Genetic threats to populations
4. Case studies

14
A. What is Genetic Diversity?

1. Among species
2. Among populations
3. Within populations
4. Within individuals

15
B. Importance of genetic diversity

• Evolutionary potential
• Loss of fitness
• Instrumental value

16
C. Genetic threats to populations

• Small Population Size
• Effective population size
• Drift Bottlenecks
• Inbreeding depression
• Loss of genetic variation
• Accumulation of harmful mutations
• Introgression and hybridization
• Outbreeding depression

17

• Small populations are subject to rapid decline
  due to
• Loss of genetic variability and related problems
• Demographic fluctuations due to random variations
  in birth death rates
• Environmental fluctuations due to variation in
  predation, competition, disease, natural
  catastrophes, etc.

18
Effective Population Size (Ne)- of breeding
individuals
Vs.
Census Population Size (Nc) actual number of
individuals in a population

• Unequal Sex Ratio
• Unequal production of offspring

19

• Bottleneck drastic reduction in population size
• Founder effect when a few individuals establish
  a new population that has less genetic variation
  than the larger original population

20

• Genetic drift random fluctuations of allele
  frequencies
• A loss of certain alleles, especially rare
  alleles fixation of others
• Reduction in the amount of variation in
  genetically determined characteristics, decline
  in heterozygosity (H)

the rate at which new (neutral) mutants are fixed
is 1/u this rate is INDEPENDENT of population
size, N.
21
Due to the fixation of certain alleles,
heterozygosity will decline in the case of
genetic drift in small populations. Ht HO 1
1/(2N)t
Ht Population A (50) Population B (10)
H0 0.500 0.500
H1 0.495 0.475
H2 0.490 0.451
H3 0.485 0.429
H4 0.480 0.407
H5 0.475 0.387
22
2. Inbreeding Depression

• Inbreeding Mating between relatives
• FI - is the probability that two copies of the
  same allele are identical by descent (IBD)
• Example FI of the offspring of a mating between
  full sibs is ¼
• F is the proportion by which heterozygosity is
  decreased, relative to that in a random mating
  population with the same allele frequency

23
Normal lion sperm Abnormal lion sperm from
an isolated, inbred population in Tanzania
Inbreeding leads to the expression of recessive
deleterious alleles that are suppressed in
heterozygotes
24
3. Introgression and hybridization

• When mating occurs between individuals that are
  too genetically dissimilar
• Loss of fitness results
• Swamping of locally adapted genes adaptive
  gene complexes in native populations are being
  displaced by the immigration of genes that are
  adapted to another environment
• Breakdown of biochemical or physiological
  compatibilities between genes in the different
  populations.

25
(No Transcript)
26
Case studies
Due to severe over hunting, by 1892 somewhere
between 8 and 20 were left. Since then there has
been an almost exponential increase, especially
in the northern colonies. In 1957 there were
13,000 elephant seals, in 1976 48,000. The
population is still not at equilibrium (Boveng et
al, 1988). In 1991, the total population was
estimated at 127,000, with 28,164 pups born that
year and there appears to be a 6 annual increase
(Stewart et al, 1994)
27
Marsh rat
Silver rice rat

• 1975, 20 individuals translocated to the island
  (4 males 16 females)
• Total population by 1999 650
• Molecular markers show that these island sheep
  are much less genetically diverse than those
  found on the mainland (H 0.67 as compared to H
  0.42)

28

• Insular populations in Sweden exhibited
  inbreeding depression symptoms
• Abnormal scales
• Decreased litter size
• Increased inviable progeny

29
- Capra ibex ibex (Austria), C. i. aegagrus
(Turkey) C. i. nubiana (Sinai)