Group 4
1).DEFINE FOOD CHAIN AND FOOD WEB.
Food chain
Food chain in a Swedish lake.Osprey feed on northern pike, which in turn feed on perch which
eat bleak that feed on freshwater shrimp.A food chain is a linear sequence of links in a food
web starting from species that are called producers in the web and ends at species that are called
decomposers in the web. A food chain also shows how the organisms are related with each other
by the food they eat. A food chain differs from a food web, because the
complex polyphagousnetwork of feeding relations are aggregated into trophic species and the
chain only follows linear monophagous pathways. A common metric used to quantify food web
trophic structure is food chain length. In its simplest form, the length of a chain is the number of
links between a trophic consumer and the base of the web and the mean chain length of an entire
web is the arithmetic average of the lengths of all chains in a food web.
Food chains were first introduced by the African-Arab scientist and philosopher Al-Jahiz in the
9th century and later popularized in a book published in 1927 by Charles Elton, which also
introduced the food web concept.
FOOD WEB
A food web (or food cycle) is the natural interconnection offood chains and generally a graphical
representation (usually an image) of what-eats-what in an ecological community. Another name
for food web is a consumer-resource system. Ecologists can broadly lump all life forms into one
of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs.
To maintain their bodies, grow, develop, and to reproduce, autotrophs produce organic matter
from inorganic substances, including both minerals and gases such as carbon dioxide.
These chemical reactions require energy, which mainly comes from the sun and largely
by photosynthesis, although a very small amount comes from hydrothermal vents and hot
springs. A gradient exists between trophic levels running from complete autotrophs that obtain
their sole source of carbon from the atmosphere, to mixotrophs (such as carnivorous plants) that
are autotrophic organisms that partially obtain organic matter from sources other than the
atmosphere, and complete heterotrophs that must feed to obtain organic matter. The linkages in a
food web illustrate the feeding pathways, such as where heterotrophs obtain organic matter by
feeding on autotrophs and other heterotrophs. The food web is a simplified illustration of the
various methods of feeding that links an ecosystem into a unified system of exchange. There are
different kinds of feeding relations that can be roughly divided
into herbivory, carnivory, scavenging and parasitism. Some of the organic matter eaten by
heterotrophs, such as sugars, provides energy. Autotrophs and heterotrophs come in all sizes,
from microscopic to many tonnes - from cyanobacteria togiant redwoods, and
from viruses and bdellovibrio to blue whales.)
2) WHAT ARE CONSUMERS IN AN ECOSYSTEM? CLASSIFY IT WITH SUITABLE
EXAMPLE.
Ans)CONSUMERS(food chain)
Consumers are organisms of an ecological food chain that receive energy by consuming other
organisms. These organisms are formally referred to as heterotrophs, which
includeanimals, bacteria and fungus. Such organisms may consume by various means,
includingpredation, parasitization, and biodegradation.
Four type of consumer in ecosystem.
Herbivores are animals that feed only on plants.
Carnivores are animals that feed on other animals.
Omnivores are animals that feed on both plants and animals.
Saprobes are organisms that get nutrients by breaking down the remains of dead plants and
animals. Examples of saprobes are bacteria and fungi.
Herbivores.
Herbivores are living organisms that mostly feed on plant based products like leaves, grass, some
fruits and shrubs.
Carnivores.
carnivores are meat eating animals that acquire their food and energy and nutrients needs of their
bodies through feeding on other animal tissues. Carnivores can either be scavengers or predators.
Scavengers are those consumers who feed on dead organisms that have either died through the
natural way or were killed by predators like the lion. The predators rarely eat dead organisms but
instead hunt and kill their pray before they eat them. The carnivores are mostly to be found in the
animal kingdom but there exists some few of them in the plant kingdom. There are carnivorous
plants that feed on such things as insects that come near them.
Omnivores.
Omnivores are types of consumers that are similar to both herbivores and carnivores in one way
or another in terms of the types of foods they happen to eat. They eat both animals and plants
products to derive energy and nutrients. Note that omnivores usually don’t eat every plant or
animal that comes their way but are selective in nature on what they prey on. They only consume
on things that good for them and their general being and avoid on food substances may not be
suitable for consumption or that poses a health threat to them. A typical example of an omnivore
is man.
Saprophytes.
Saprophytes are types of consumers or organisms that generally get their food and nutrients from
decaying or non living organisms. Fungi are a good example of a saprophyte.
3) WHAT ARE ECOLOGICAL PYRAMIDS? EXPLAIN WHY SOME OF THESE
PYRAMIDS ARE UPRIGHT WHILE OTHERS ARE INVERTED IN DIFFERENT
ECOSYSTEMS?
Ans) An ecological pyramid (also trophic pyramid, energy pyramid, or sometimes food pyramid)
is a graphical representation designed to show the biomass orbiomass productivity at
each trophic level in a givenecosystem.
Biomass is the amount of living or organic matter present in an organism. Biomass
pyramids show how much biomass is present in the organisms at each trophic level,
while productivity pyramids show the production or turnover in biomass.
Ecological pyramids begin with producers on the bottom (such as plants) and proceed through
the various trophic levels (such as herbivores that eat plants, then carnivores that eat herbivores,
then carnivores that eat those carnivores, and so on). The highest level is the top of the food
chain.
An ecological pyramid of biomass shows the relationship between biomass and trophic level by
quantifying the biomass present at each trophic level of an ecological community at a particular
time. It is a graphical representation of biomass (total amount of living or organic matter in an
ecosystem) present in unit area in different tropic levels. Typical units are grams per meter,or
calories per meter. The pyramid of biomass may be "inverted". For example, in a pond
ecosystem, the standing crop of phytoplankton, the major producers, at any given point will be
lower than the mass of the heterotrophs, such as fish and insects. This is explained as the
phytoplankton reproduce very quickly, but have much shorter individual lives.
One problem with biomass pyramids is that they can make a trophic level appear to contain
more energy than it actually does. For example, all birds have beaks and skeletons, which despite
having mass are not eaten by the next trophic level.
There is also pyramid of numbers which represent the number of organisms in each trophic level.
They may be upright (e.g. Grassland ecosystem), inverted (parasitic ecosystem) or dumbbell
shaped (forest ecosystem).
Inverted Ecological Pyramids.
The concept of the ecological pyramid is one of the most important models described in ecology.
Classically defined, biomass and energy pyramids are wider at the bottom. This indicates that
there are more prey items than predators in a given environment, with cumulative biomass
andenergy content being greater in prey than predators.
Inverted pyramids have predators stably outnumber prey, with the most biomass locked up in the
highest rung.i.e.:This inverted scheme goes against the convention generally taught in basic
biology, and for good reason. They’re rare, and, in fact, their existence is debatable, depending
upon semantics.
A popular example of biomass inversion comes from aquatic environments (particularly closed
off, nutrient poor lakes). Here, phytoplankton, the primary producers, can be much reduced in
biomass compared to the planktivores that eat them.This is usually explained by the high
turnover of plankton numbers. Their rapid synthesis and mortality ensures that, although their
overall biomass is less, because of the fast rates of death and reproduction, more ENERGY is
going through these lower rungs. So the energy throughput of the phytoplankton is
greatestamongst pyramid levels.
Conversely, predators live longer, grow slower, and arepredated less often, so it may appear as
though there is more biomass there, but the energy flowing through the top is reduced.
This shows that energy pyramids arealways bottom up and can never be inverted.Nature is
inefficient. Due to requirements of organisms to “waste” energy maintaining homeostasis (for
starters), not all the energy taken from the lower food level gets transferred to the next one up.
Another familiarly published inverted system describes coral reef habitats, whereshark
populations see significantly more accumulated biomass than those of smaller reef fish
species.Problems with the inversion concept include mobile predators with access to multiple
ecosystems, inconsistent ratios between predator/prey mass [i.e., in a lake, there may be less
algae than small fish (inverted scheme), but there are more small fish than top predators
(normal), resulting in only a partially inverted biomass pyramid], and just a lack of
understanding of the full complexities of food chains.
4) EXPLAIN THE ENERGY FLOW IN AN ECOSYSTEM WITH A SUITABLE EXAMPLE.
Ans)(pdf. File attached)