1. CHAPTER 2 DISTRIBUTION & ABUNDANCE

2. Learning Outcome To understand the concepts of adaptation-tolerance
To be able to relate between biogeography and how it affect distribution and abundance.
To understand Transplant experiment.

3. Adaptation = The set of characteristics (biochemical, physiological, morphological and behavioral) that enables an organism to maximize its fitness under one set of environmental conditions.
Long neck of giraffe -to feed in areas that cannot be reached to other animals.
White coat of polar bear -makes it invisible to potential prey, increase its capability to hunt or search for food in the Arctic.
Modern corn - Native Americans only planting seeds from those with the most kernels and discarding the rest.

4. Polar bear- similar to grizzly bears, made their way up north
Polar bear- similar to grizzly bears, made their way up north. Due to the harsh artic conditions, over the next 20,000 years the brown bear evolved to have a thicker coat to fight the cold and lighter fur to blend in with it's surroundings.
Corn- Their goal was to improve the ear and its kernels. A teosinte ear is only 2 to 3 inches long with five to 12 kernels, compare that to modern domesticated corn's 12-inch ear that boasts 500 or more kernels!

5. Concept of Adaptation- Range
Why is the range of some organisms wide while for others is narrow for environmental conditions?
This is related to the adaptive ability of the species

6. Concept of Adaptation- Fitness
Among reproducing individuals some will leave more offspring than others - fitness
A measure of the contribution to the gene pool and to future generation.

7. Link between Natural Selection and Adaptation
NS- differential success (survival and reproduction) of individuals in a population within a given environment.
Evolution- changes in any attribute of a population over time (genes/allele). Leads to adaptation in population over generations.
Adaptation and tolerance

8. 3 important law which affect distribution and abundance: 1) Law of the Minimum (Liebig) 2) Law of Limiting Factors (Blackman) 3) Law of Tolerance (Shelford)

9. 1. Law of the Minimum (Liebig)
The rate of any biological process is limited by that factor in least amount relative to requirements.
There is only one limiting factor at any one time.
Additions of other environmental factors will not increase growth until the amount of the limiting factor is increased.

10. Law of the Minimum- Liebig
Liebig compare the potential of a crop to a barrel with staves of unequal length.
The capacity of this barrel is limited by the length of the shortest stave (in this case, phosphorus) and can only be increased by lengthening that stave.
When that stave is lengthened, another one becomes the limiting factor.

11. 2. Law of Limiting factors (Blackman)
=maximum quantity of a resource tolerated by an organism would also limit response as well.

12. Law of Limiting factors (Blackman)
As the light intensity (LI) increases, the rate of p/s increases, until the plant is photosynthesizing as fast as it can.
LSP - Light Saturation Point. When the LSP is reached, plants cannot photosynthesize any faster, even when the light gets brighter.
- max. quantity of light that the plant can tolerate
Light intensity
P/s rate

13. 3. Law of Tolerance (Shelford)
Law of Tolerance = combination of Law of the Minimum and Law of Limiting Factors:
illustrated by a bell shaped curved
difference in tolerance for organism which are:
Zone of intolerance (Organism absent)
Survival
Growth
Greatest fitness = The zone of greatest fitness is areas in which is the most optimum time for reproduction or fitness.

15. Tolerance ranges are not fixed:
- as seasons and conditions change, individuals may acclimate by shifting their tolerance ranges.
All these shifts takes place within the adaptive physiological (functional) limits.
This short term response to changing environments is termed as acclimatization (adaptation)

16. Tolerance ranges are usually narrow for juveniles of many species.
Broad tolerance range = able to exist within a wide range environmental factor (salinity, temperature or humidity).
eg blue crab (Callinectes sapidus) and seabass/baramundi (Lates calcarifer) : can survive in marine to freshwater.
Tolerance ranges are usually narrow for juveniles of many species.

17. Eury = wide tolerance (euryhaline, eurythermal).
Steno = narrow tolerance (stenohaline, stenothermal).
Eg.: Salmon eggs and larvae in freshwater (Stenohaline) while adults in marine (Euryhaline)
Organisms with a wide range of tolerance - widely distributed

18. Ecotype
Definition: A subspecies or race that is especially adapted to a particular set of environmental conditions.
Due to evolutionary relationship the more closely related species are almost similar in tolerance.

19. Four (4) constraints to Adaptation:
Genetic forces : mutation and gene flow prevent adaptation – most mutation are detrimental rather than adaptive.
Changing environment : Environments are continuously changing.
Adaptation is a compromise : gain in one and lose at another. e.g, a loon, a type of bird have wings that are adapted for diving but not so efficient for flying.
Historical constraints : all organisms have a history and change in small increments

20. Coevolution/Arms Race
Mutual evolutionary = evolution of two species totally dependent on each other.
Each of the species involved puts selective pressure on the other, so they evolved together
Example:
herbivore and food plants
predator-prey,
host-parasite

21. Example 1: Coevolution/Arms Race (Host-Parasite)
Brown-headed cowbirds in North America. They carve a living by following herds of bison or cattle, and feeding off the insects that the beasts attract.
Nomadic life-style: This makes bringing up young problematic.
They get over this obstacle by becoming "brood parasites". In other words, they recruit different bird species to unwittingly raise their young.
Very simply, they lay their eggs in the nest of an unsuspecting song-bird, like the eastern phoebe, and leave.
The cowbirds lay their eggs in the nest of an unsuspecting song-bird and leave
A type of parasitic bird, which is reared by unrelated host "parents", is happy to share its nest with the host's babies,

22. Example 1: Coevolution/Arms Race (Host-Parasite)
Parasitic birds lay their eggs that closely mimic those of the host and young with characteristics that encourage the hosts to feed them (same color, size and pattern as host)
The hosts then provide parental care to the unrelated young that hatch from the parasitic egg, often to the detriment of their own young
Both parasite (cowbird chick) and host sp (song bird chick) are continually evolving counter-strategies for survival

23. Example 1: Coevolution/Arms Race - selfish reason
Cowbirds who share their nest with another host chicks actually succeed: they grow much faster than cowbird chicks reared alone.
This is because the host parents work disproportionately hard to feed a full nest.
And, because the cowbird chick is rather more robust, it gets more than its share of the food.
Cowbird gained disproportionately from the higher provisioning because it could overpower the host young, and take more than its fair-share of food."

24. Example 2: Coevolution/ Arms Race (Mutualistic)
Yucca moths (pollinator) and yucca plants (provide home, food)
Yucca flowers are a certain shape so only
-that tiny moth can pollinate them.
The moths lay their eggs in the yucca flowers and
- the larvae (caterpillars) live in the developing ovary and eat yucca seeds.

25. Example 3: Coevolution/Arms Race (Mutualistic)
Acacia ants (protector) and acacia trees (provide home, food)
Acacias are small, Central American trees in the Leguminosae.
They have large, hollow thorns. The acacia ants live in the thorns.
On the tips of its leaflets, the plant makes a substance used by the ants as food.
The ants defend the tree from herbivores by attacking/stinging any animal that even accidentally brushes up against the plant.

26. Example 4: Coevolution/Arms Race (Mutualistic- Plant and Pollinator)
Many plants depend on animals to spread their pollen.
This is a mutualistic relationship where the plant and the pollinator benefit each other.
The plant expends less energy on pollen production and instead produces showy flowers, nectar, and/or odors.
Some plants/flowers are more general, while others are more specific.

27. Units of Selection
Darwin said that natural selection operates through reproduction and survival of individuals who differ genetically – individual selection – most important (Darwinian selection)
Natural selection is not only restricted to individuals but can act on any biological unit as long as:
they can replicate/reproduce/divide
produce more than replacement needs
survival depends on some attribute (size, colour, behavior)
a mechanism allows for the transmission of the attributes

28. Three (3) Units of Selection
Gametic
Kin
Group

29. 1. Gametic Selection
eggs and sperm (n) have genetic composition that differs from the diploid (2n) organisms that produce them
natural selection can act on the gametes – sperm mobility, pollen that produce faster growing pollen tube so it will have better chance for sperm and egg fusing

30. 2. Kin Selection
Individuals that increase the survival or reproduction of its relatives
Natural selection favors alleles that benefit an individual but also alleles that benefit close relatives of that individual that share alleles
Altruistic traits – alarm call
Ground squirrel see a predator they give an alarm call
Draws attention to itself (detrimental to itself)
Warns nearby squirrels to run for cover – beneficial to relatives
Effects social organization and population dynamics

31. 3. Group Selection
When populations of a species are broken up into discrete groups more or less isolated from one another
Not an important force shaping in adaptation for the distribution and abundance of organisms

32. Species

33. The Species Concept Definition:
A group of populations whose individuals have the potential to interbreed and produce viable fertile offspring but are unable to produce viable fertile offspring with members of other populations.

34. Sturnella magna
Sturnella neglecta
(a)
Similarity between different species. The eastern meadowlark (Sturnella magna, left) and the western meadowlark (Sturnella neglecta, right) have similar body shapes and colorations. Nevertheless, they are distinct biological species because their songs and other behaviors are different enough to prevent interbreeding should they meet in the wild.
Diversity within a species. As diverse as we may be in appearance, all humans belong to a single biological species (Homo sapiens), defined by our capacity to interbreed.
(b)

35. Reproductive Isolation
Isolating mechanisms – morphological characteristics, behavioral traits, ecological conditions, genetic incompatibility.
These mechanisms could be pre-mating or post mating
Pre-mating/Prezygotic : prevents mating between diff sp.
Post-mating/Post zygotic : reduces the survival or success of offspring that results from mating between 2 diff sp.

36. Premating mechanisms 1)HABITAT SELECTION
- Isolation through differences in habitat is common among frogs and toads
Different calling and mating sites among breeding frogs and toads tend to keep the species separated

39. Frogs
The upland chorus frog and the southern chorus frog breed in the same pools, but tend to separate themselves in different locations in the pond
- The upland chorus frog calls from a more open location while southern chorus frog calls from a concealed position at the base of the grass or debris of vegetation.

40. Premating mechanisms 2) TEMPORAL ISOLATION
Difference in the timing of breeding and flowering seasons
E.g, the American toad (Bufo americanus) breeds early in the spring
while Fowler’s toad (Bufo woodsei fowleri) breeds a few weeks later than the American toad

41. Premating mechanisms 3) BEHAVIORAL BARRIERS
Difference in courtship and mating
The males of many animals have specific courtship displays and mostly only females of the same species respond
- Example of displays: visual, auditory or chemical stimuli
Visual signals developed by birds and some fish
Birds, frogs, and toads, crickets, grasshoppers, cicadas have specific calls that attract only the correct species
Some insects, i.e butterflies, fruit flies and some mammals possess species-specific scent

42. Premating mechanisms 4) Mechanical isolating mechanism
Difference in floral structure eg. Umbel (Lily), Corimb (Bunga tahi ayam; Lantana sp.,)
- Make copulation and pollinating between closely related species impossible

43. Individuals of different species
Prezygotic barriers - slow down mating or obstruct fertilization if mating does occur
Individuals of different species
Mating attempt
Habitat isolation
Temporal isolation
Behavioral isolation
Mechanical isolation
Prezygotic and postzygotic barriers
HABITAT ISOLATION
TEMPORAL ISOLATION
time of breeding or
flowering season
BEHAVIORAL ISOLATION
- Courtship and mating
MECHANICAL ISOLATION
Prevent pollination
prevent copulation
(b)
(d)
(e)
(g)
(f)
(a)
(c)

44. Reduce hybrid viability Reduce hybrid fertility
Viable fertile offspring
Reduce hybrid viability
Reduce hybrid fertility
Hybrid breakdown
Fertilization
Gametic isolation
GAMETIC ISOLATION
REDUCED HYBRID VIABILITY
– capacity for surviving
- Germinating under favorable condition
REDUCED HYBRID FERTILITY
HYBRID BREAKDOWN
(hybrids – generally do not survive and if survive are infertile – horse + donkey=mule (baghal).
(k)
(j)
(m)
(i)
(l)
(h)

45. Speciation – Involves Reproductive Isolation
According to Darwin, speciation is the divergence of existing species through natural selection (natural event)
Critical step of genetic isolation is when the gene pool of one population becomes isolated from the parent population.

47. Explanation for (a)
Imagine a piece of land, warm and dry occupy by species A
At some point of geological time, mountains uplift and land sink and floods with water
This cause the splitting of the original land of parent population and separates species A from the rest of the population and will become the subpopulation A’
A’ now occupies a cool, moist climate different from the original population
Natural selection will favor individuals best adapted to cool and moist climate, similar selection as well for dry climate

48. Explanation for (b)
If geological barrier breaks down and the two populations rejoin before natural selection results in difference that cause reproductive isolation,
- the two populations may merge into one population back again

49. Explanation for (c)
If sufficient differences occur that does not allow breeding to happen, then the two populations will be separated even if they do come together again

50. Speciation can take place with or without geographic separation
Speciation can occur in two ways
Allopatric speciation
Sympatric speciation
(a)
Allopatric speciation.
A population forms a new
species while geographically isolated
(b)
Sympatric speciation.
A small population becomes a new species without geographic separation.

51. Speciation Allopatric species
– occupy areas separated in space and time
– subpopulation becomes geographically isolated from original/parent pop

52. Speciation Sympatric species
– occupy same area at the same time and may have chance to interbreed
– subpopulation becomes a new species without geographic separation.