Age structured populations, habitat and niche, niche types, diff bw fundamental and realized niche, niche width and overlap, competitive exclusion principle, resource partioning and its types, character displacement.

1. Plant Ecology
important terms
M.SC BOTANY

2. Age-structured populations

3. Both age structure and age pyramids can take a variety of forms,
depending on the birth and death trends within the population, as
well as a host of other social factors.
They can be:
•stable: patterns of birth and death are unchanging over time
•stationary: both low birth and death rates (they slope gently
inward and have a rounded top)
•expansive: slope dramatically inward and upward from the
base, indicating that a population has both high birth and death
rates
•constrictive: signaling low birth and death rates, and expanding
outward from the base before sloping inward to achieve a rounded
peak at the top

4. There are three types of age structures, viz.,
(i) the West European type in .which children constitute less than 30
per cent, and 15 per cent of the population are old;
(ii) the North American type where 35-40 per cent of the population
are children and ten per cent, old people; and
(iii)the Brazilian type where 45-55 per cent of the population are
children, and old people constitute only four-eight per cent of the
total population.
The type of age structure has a direct influence on the future of a
nation, since both extremes, i.e., old age dependency as well as young
age dependency proves to be a severe burden on the economy of a
country.

5. Fundamental Niche
Realized Niche
Where the organism
lives
No Yes
Size Large Small
Competition for
resources, predators
are present
No Yes
Other terminology Precompetitive niche Postcompetitive niche

6. Habitat Niche
A habitat is a particular place
where organisms live, i.e. address
A niche defines a particular role
played by organisms in an
ecosystem, i.e. profession
Habitat is not a species-specific
and many species can occupy the
same habitat
Niche is a species-specific and it
supports only a single species
Habitat consists of several niches Niche is specific to a particular
species, which may overlap with a
similar niche but must have
distinct differences
Habitat is a superset of niche Niche is a subset of habitat
Examples: desert, ocean,
mountains, grassland, forest, etc.
Examples: different trophic
position occupied by Darwin’s
finches

7. Fundamental vs. Realized Niche
 Both fundamental and realized niches refer to the environmental position
that species occupy in an ecosystem.
 Fundamental niches represent all the environmental conditions where a species is able
to live,
 the realized niche is where the species actually lives.
 Other names for these niches are precompetitive and postcompetitive, respectively.
 In a fundamental niche, an organism can take advantage of all the biotic and abiotic
factors in an ecosystem without competition from other species or pressure from
predators.
 This niche narrows when other organisms arrive and there is competition for food and
breeding partners or when predators start hunting in the area.
 The organism will survive if it adapts to the new conditions of its realized niche.

8.  Fundamental niches are the same size or larger than realized niches.
 Also, the same species living in different locations may have different realized
niches depending on the competitors and predators that are present.
 Fundamental and realized niches can be wide or narrow.
 Specialist species is the term for organisms that live in narrow niches because they
thrive only in certain environmental conditions or eat a certain food.
 Conversely, generalist species occupy wider niches and make use of a variety of
resources and can live in many different environmental conditions.
 The niche that an organism occupies may change dramatically over the course of
its life.
An example of this is when a tadpole which is an herbivore,
undergoes metamorphosis into a carnivorous frog.

9. What is a Realized Niche.
Realized niche or post-competitive niche is the range of
environmental conditions in which the species actually live. It is
always smaller than the corresponding fundamental niche of the
species and is considered as a subset of the fundamental niche.
What is fundamental and realized niche?
Fundamental niche refers to a niche of an organism given that there are no
limiting factors on the environment or resources the organism can use while a
realized niche refers to a niche a viable population of a species occupies in
the presence of competitor species.
This explains the basic difference between fundamental niche and realized
niche

10. What is the difference between fundamental and realized
niche?
Moreover, a further difference between fundamental and
realized niche is that the fundamental niche describes the
various ecological roles that a species can attain. On the
other hand, realized niche describes the ecological roles that
a species is actually doing.
Can an organism survive with its realized niche?
The organism will survive if it adapts to the new conditions of its realized niche.
Fundamental niches are the same size or larger than realized niches. Also, the
same species living in different locations may have different realized niches
depending on the competitors and predators that are present.

11. o As an example, the male red-winged blackbird holds the prime real estate in
the marshes in the early spring.
o However, with the seasonal progress, tri-color blackbirds, which are more
aggressive move, into the marshes and take over the best territory.
o Hence, before the arrival of the tri-color blackbird, the marshes are a
fundamental niche for the male red-winged blackbird.
What is a Fundamental Niche
 Fundamental niche or pre-competitive niche is the range of
environmental conditions in which a particular species can live.
 This means it defines a collection of conditions and sources in which the
species can survive, grow, and reproduce.
 The organisms in the species can take the maximum advantage of
both biotic and abiotic factors in the ecosystem of the fundamental niche
since there is no competition for resources and predators.

13.  What is a Realized Niche
 Realized niche or post-competitive niche is the range of environmental conditions in
which the species actually live.
 It is always smaller than the corresponding fundamental niche of the species and is
considered as a subset of the fundamental niche.
 When the species in the fundamental niche has to face various interactions and pressure
from the environment, it is forced to move into a small niche, the realized niche.
 Also, it is considered that with the growth of the realized niche, the corresponding
fundamental niche also grows accordingly.
As an example, wolves ranged across North America competing well with
coyotes for food and territory. With the arrival of European settlers to the
continent, the hunting reduced the wolf population, letting coyotes enjoy a
wide range of environment.

14. Competition for Resources
There is no competition in a fundamental niche either for resources or
predators while a competition occurs for both resources and predators
in a realized niche. This is an important difference between
fundamental niche and realized niche.
Conclusion
 Fundamental niche is a theoretical niche that includes any type of ecological
positions in which a particular species can live.
 On the other hand, realized niche is the actual ecosystem where the species live. In
addition, there is no environmental pressure in the fundamental niche and
 when the pressure occurs either from predators or limited resources, the species
moves to the realized niche.
 The main difference between fundamental niche and realized niche is where the
species live and the type of environmental pressure.

16. Definition of Habitat
 A habitat is a place or area where a species grows, lives or thrives.
Temperature, sunlight, rainfall, types of soil, etc. and other abiotic factors
determine the presence of organisms present in an area.
o These factors prevailing in an area determine the best-suited species for
that environment.
 Habitat is the best-suited condition for a species and provides ideal
conditions for a species to grow, adapt, reproduce and flourish.
 It is the energy or nutrient providing area for an organism. Habitat of a
species describes the totality of abiotic factors to which the species is
exposed in the area.
o Examples of habitat include desert, ponds, freshwater lake, ocean,
mountains, grassland, forest, etc.

17.  Ecological Niche
 The niche is the way of life of a species marked by the set of
conditions, resources and interactions it requires.
 Every species fits into its ecological community and can tolerate
various environmental factors to a certain extent.
 For eg., a fish species niche is classified on the basis of a specific
salinity range, pH, temperature and type of food it consumes.
 If two organisms have the same niche, it is very difficult for them to
survive in the same environment due to the competition.

18. Definition of Niche
o Joseph Grinnel coined the term “Niche”. He described a niche as the
distributional unit specific to each species.
o He emphasised that no two species living in the same territory can
occupy the same ecological niche for long.
o The ecological niche not only involves the physical space occupied by
an organism but it also describes the functional role or place of a
species in its community structure.
o This includes everything related to how it influences a community, i.e.
what it eats, where it lives, what it does, the trophic position occupied,
etc.
o Niche describes how a species contributes to the energy flow of the
system, how it gains energy and supplies it further in an ecosystem.
 There are three aspects of an ecological niche:

19.  Spatial or habitat niche: It accounts for the physical space occupied
by an organism.
 This explains the different microhabitat owned by several species
having identical general habitat.
 E.g. seven species of millipedes reside in the same general habitat of
the forest floor of a maple oak forest and all are decomposers,
 i.e. occupy the same trophic level but predominate in their specific
microhabitat that is created by several gradients in the decomposition
stage.

20. o Trophic Niche: It tells about the functional role or trophic position
occupied by a species.
o It explains how different species share the same habitat but occupy
different trophic niches.
o E.g. Darwin’s finches of Galapagos islands. These birds belong to the
same genera and live in the same general habitat but differ in their
eating habits, i.e. trophic position.
o One species is vegetarian feeding on buds and fruits and others are
insect eaters, feeding on insects of different sizes.
o There is a woodpecker finch, which has a wood-pecking beak.

21.  Hypervolume or multidimensional niche: It represents the position of a species
in the environmental gradient. There are a large number of environmental factors,
both abiotic and biotic, that affect the population. This is the fundamental niche of
the species and refers to the totality of abiotic and biotic factors to which a given
species is uniquely adapted.
Niche is specific to a particular species, no two species can fill the
same niche. The two similar niches can overlap but there must be
distinct differences to avoid competition for the same resources.

22. What is niche overlap in ecology?
Niche overlap is an important concept in community ecology because it is
expected to determine how many and which species can coexist in a
community.
Interest in niche overlap began with the competitive exclusion principle, which
states that two species using identical resources and/or environments cannot
coexist

24.  What is an example of competitive exclusion?
 Example: Plants consume extra nitrogen, hence leaving nothing for other
plants in that area. Noted Russian ecologist G. F. Gause, in 1934, proposed
the principle of competitive exclusion. He stated that species cannot coexist if
they have the same niche. By niche, he meant the food and the environment
(temperature, pH) required to breed.
What are two types of competition according to competitive exclusion
principle?
 There are two kinds of competitions according to the competitive exclusion
principle: Intraspecific and interspecific.
 Intraspecific is a competition amongst beings of the same species.
 This type shows changes in the population size over time.

25.  In ecology, the competitive exclusion principle, sometimes referred to as
Gause's law, is a proposition named for Georgy Gause that two species
competing for the same limited resource cannot coexist at constant
population values.
 When one species has even the slightest advantage over another, the
one with the advantage will dominate in the long term.
 This leads either to the extinction of the weaker competitor or to an
evolutionary or behavioral shift toward a different ecological niche.
 The principle has been paraphrased in the maxim "complete competitors
can not coexist".

26.  The niche width of an organism refers to a theoretical range of conditions that
a species could inhabit and successfully survive and reproduce with no
competition.
 The niche width is defined as the parameters of this range which are determined
by biotic and abiotic factors such as appropriate food sources and suitable
climate respectively.
What is niche width?
Realized niche width is a phrase relating to ecology defining the actual
space that an organism inhabits and the resources it can access as a
result of limiting pressures from other species (e.g. superior competitors).

29. What is resource partitioning?
Resource partitioning is the division of limited resources by
species to avoid competition in a particular environment.

31.  Resource Partitioning
 If one or both the species belonging to the same niche evolve to use
different resources or develop different feeding habits, competitive
exclusion can be avoided.
 Due to this evolution, the species start using non-overlapping resources
resulting in different niches. This is termed a Resource Partitioning. This
helps the species to exist together.
 For eg., The island of Puerto Rico is the abode for a large number of
anole lizards.
 They evolved over time due to natural selection and differentiated into 11
species that use different resources and live in different habitats. This is
one fine example of Resource Partitioning.

34. Key Takeaways
•The division of resources by species to help avoid competition in an ecological
niche is called resource partitioning.
•Intraspecific competition denotes competition for resources by individuals of
the same species.
•Interspecific competition is the competition for resources by individuals of
different species.
•By studying resource partitioning, scientists can understand how the addition
or removal of a species may impact the overall usage of resources in a given
habitat or niche.

35. Long-Term Effects of Resource Partitioning
By partitioning out resources, species can have long-term coexistence with one
another in the same habitat. This allows both species to survive and thrive
rather than one species causing the other to go extinct, as in the case of
complete competition. The combination of intraspecific and interspecific
competition is important in relation to species. When different species occupy
slightly different niches in relation to resources, the limiting factor for
population size becomes more about intraspecific competition than
interspecific competition.
Similarly, humans can have profound effects on ecosystems, particularly in
causing species to go extinct. The study of resource partitioning by scientists
can help us understand how the removal of a species may impact the overall
allocation and usage of resources both in a particular niche and in the broader
environment.

36. Habitat Partitioning Examples
 One way that species can partition resources is by living in different
areas of a habitat versus their competitors.
 One common example is the distribution of lizards in the Caribbean
islands.
 The lizards mostly eat the same types of food—insects. However,
they can live in different microhabitats within the context of their
larger habitat.
 For example, some lizards can live on the forest floor while others
may live higher up in the habitat in trees.
 This differentiation and partitioning of resources based on their
physical location allows the different species to coexist more
effectively with one another.

37. Food Partitioning Examples
 Additionally, species can more effectively coexist based on food
partitioning. For example, among species of lemur monkeys, food may be
discriminated by the chemical characteristics of the food. Food
partitioning based on plant chemistry can play an important role. This
allows different species to coexist while eating similar yet chemically
different foods.
 Similarly, species may have an affinity for different parts of the same food.
For example, one species may prefer a different part of the plant than
another species, allowing them to effectively coexist. Some species may
prefer the leaves of the plant while others prefer the plant stems.
 Species can also partition food based on other characteristics such as
different activity patterns. One species may consume most of their food
during a certain time of day while another may be more active at night.

38. When species compete for the exact same resources, one species typically has the
advantage over another, even if only slightly so. The complete competition maxim states
that complete competitors cannot coexist. The species with the advantage will persist in
the long term. The weaker species will either become extinct or will transition to
occupying a different ecological niche.
When organisms compete for limited resources, there are two primary types of
competition: intraspecific and interspecific. As the prefixes denote, intraspecific
competition refers to competition for limited resources by individual organisms of the
same species, while interspecific competition refers to the competition for limited
resources by individuals of different species.
Resource Partitioning Definition
The original concept of resource partitioning refers to the evolutionary adaptations in
species as a response to the evolutionary pressure from interspecific competition. The more
common basic biological usage is based on the different uses of resources by species in a
particular niche and not on the specific evolutionary origin of such differences. This article
explores the latter convention.

39. Character displacement

40. What is character displacement?
 “Character displacement is the situation in which, when two
species of animals overlap geographically, the differences
between them are accentuated in the zone of sympatry and
weakened or lost entirely in the parts of their ranges outside this
zone”.
 An outcome of competition in which two species living in the same
area have evolved differences in morphology or other characteristics
that lessen competition for food resources.
Who discovered character displacement?
Character displacement was first explicitly explained by William L. Brown
Jr. and E. O. Wilson in 1956: "Two closely related species have
overlapping ranges.

41.  Character displacement occurs when similar species that live in the
same geographical region and occupy similar niches differentiate in
order to minimize niche overlap and avoid competitive exclusion.
 Several species of Galapagos finches display character displacement.
 Each closely related species differs in beak size and beak depth,
allowing them to coexist in the same region since each species eats a
different type of seed: the seed best fit for its unique beak.
 The finches with the deeper, stronger beaks consume large, tough
seeds, while the finches with smaller beaks consume the smaller, softer
seeds.

43. The Process of Character Displacement
(a) Initially, two species encounter each other and overlap in
phenotypes associated with resource use or reproduction, indicated
here by the two overlapping bell-shaped curves.
 Character displacement arises when individuals most dissimilar
from the average resource-use or reproductive phenotypes of
another species are more successful at acquiring resources or at
reproducing than other members of their population.
(b) Consequently, the most divergent individuals should experience the
highest fitness, and the two species should evolve to be less similar to
each other.
 Character displacement is indicated when the differ- ence between
species in mean trait value is greater after selection ( d A ) than
before selection ( d B ).

44. Six criteria have been developed to establish character displacement
as the mechanism for differences between sympatric species.
(1) Differences between sympatric taxa are greater than expected by
chance.
(2) Differences in character states are related to differences in
resource use.
(3) Resources are limiting and interspecific competition for these
resources is a function of character similarity.
(4) Resource distribution are the same in sympatry and allopatry such
that differences in character states are not due to differences in
resource availability.
(5) Differences must have evolved in situ.
(6) Differences must be genetically based.