Download File - chemistryattweed

A Local Ecosystem Part 2
Each local aquatic or terrestrial ecosystem is unique

examine trends in population estimates for some plant and animal species within an
ecosystem
Populations of organisms do not remain at a constant level within an ecosystem. Many
factors may affect their numbers.
o When the same species is found in an ecosystem year after year in approximately
the same numbers, scientists say the population is stable or in balance.
o Sometimes the numbers in a population increase dramatically; we refer to
this as a population explosion.
o Population numbers may also decline. Disease, predation, competition from
other species, and human activities can all contribute to the decline and
possible extinction of an organism in an ecosystem.
Grey Mangrove forest at Homebush Bay:
o As the water level rose, the amount of mangrove seedlings decreased,
but the amount of semaphore crabs increased
o As the water level reduced, the amount of mangrove seedlings increased,
but the amount of semaphore crabs decreased
o This pointed out that mangrove seedlings do not prefer to be covered in
water, while crabs do
o Summarise one other population trend from the textbook, p19.
1

outline factors that affect numbers in predator and prey populations in the area
studied
o The amount of food available
o The salinity of the water
o The amount of water available
o The reproductive cycles of both prey and predator affect their numbers.
Large numbers of young prey may be followed by an increase in predator
numbers. The prey are eaten, their numbers decline, and numbers of
predators then also decrease.
o There is often competition between predators for the same prey. For
example, cormorants and gannets compete with large fish for the smaller
fish they all prey on.
2
o Diseases can affect both predators and/or prey. If prey are affected, then the
food supply for predators will be less and they will also decline in number. If
predators are affected, the numbers of prey will increase.
o Seasonal migrations of predators or prey will affect populations. When
prey are abundant, some predators might move into an ecosystem to take
advantage of the abundance.

identify examples of allelopathy, parasitism, mutualism and commensalism in an ecosystem
and the role of organisms in each type of relationship
Allelopathy:
o This is the production by a plant of specific chemicals (allelo-chemicals)
which inhibit the growth of other plants around it.
o The example studied was the Casuarina. Its leaves contain allelo-chemicals, so
as they dropped to the floor, they released the chemicals, preventing the
growth of other plants in the area.
3
Parasitism:
o This is a relationship between two organisms where one benefits at the
expense of the other organism.
o The example studied was the pimple wasp. It lays its eggs on the leaves of
the mangrove. The larvae eat through the leave when they hatch and the
leaf is damaged.
Symbiosis
o Symbiosis is a type of interaction between organisms where two different
species live together in a close association. The association benefits at least one
of them, and the other is not disadvantaged. The two common types of
symbiosis are commensalism and mutualism.
Mutualism:
o A relationship between two organisms where both of them benefit.
o The example studied was lichen. This consists of a fungus and an alga
joined together. The fungi provides structure and the alga provides food.
Commensalism:
o A relationship between 2 organisms where only one benefits, and the other
gets no harm and no benefit.
o The example studied is the golden orb-weaving spider and the dewdrop
spider. The weaving spider makes a web, and catches its prey with it. It
leaves scraps behind. The dewdrop spider eats the leftovers.

describe the role of decomposers in ecosystems
Bacteria and fungi secrete digestive enzymes that break down detritus
(dead organic matter) into soluble organic molecules such as sugars,
and eventually into inorganic molecules such as carbon dioxide and
nitrogen.
o Decomposers are the rubbish cleaners of the ecosystems
o They feed on the left overs of other organisms, dead organisms and
decaying organisms and their wastes.
o They enable the materials of decomposition available to plants
o They keep the biomass in circulation.
4

explain trophic interactions between organisms in an ecosystem using food chains,
food webs and pyramids of biomass and energy
Trophic interactions are feeding relationships between organisms
o A FOOD CHAIN represents the flow of energy from one living thing to the next.
o Food chains start with t h e s u n t h e n t h e producers (plants), which are
eaten by herbivores, which are eaten by carnivores.
o The first consumer is the organism that eats the first other organism. It is
usually a herbivore.
Food Webs
o Food webs are a complex set of interacting food chains within an ecosystem
o Animals are consumers. An organism that feeds on plants is a first-order
consumer. An organism that feeds on a first-order consumer is called a secondorder consumer, and so on. The level occupied by a consumer in a food chain is
referred to as a feeding or TROPHIC level. First-order consumers occupy the first
trophic level; second-order consumers occupy the second trophic level, and so on.
5
o Ecosystems are composed of food webs, not just food chains.
o At every step of a food chain, energy is lost
o It is lost as heat, and waste
o This is represented in an energy pyramid, as the lowest level is the biggest,
and the levels shrink as they go up
o At every step of the food chain, biomass (mass of organisms) is lost
o Biomass is lost as undigested material and wastes
o This is also shown in a biomass pyramid
o Biomass pyramids and energy pyramids are usually similar in ecosystems
Biomass
Biomass is the amount of living material in an organism or group of organisms at any one
time. The amount or mass of living plant material produced by photosynthesis in an
ecosystem is the plant biomass.
Biomass is an estimate of the amount of matter in a given population of organisms.
Biomass for different trophic levels is compared in a biomass pyramid. A biomass
pyramid shows how the quantity of matter in living things changes along a food chain.
6
Biomass Pyramid
Energy Pyramid
Energy is lost as heat and waste.
7

define the term adaptation and discuss the problems associated with inferring
characteristics of organisms as adaptations for living in a particular habitat
o An adaptation is a feature of an organism that makes it well suited to its environment
and lifestyle.
o An adaptation may be structural – a physical characteristic relating to the structure of
an organism’s body, e.g. skin colour, shape and body covering.
o An adaptation may be physiological - related to the way the organism functions, e.g.
(e.g., making venom, secreting slime, being able to keep a constant body
temperature).
o An adaptation may be behavioural - how an organism responds to its environment.
o Adaptations help and organism to survive and reproduce in an ecosystem.

identify some adaptations of living things to factors in their environment

identify and describe in detail adaptations of a plant and an animal from the local
ecosystem
Adaptations are inherited characteristics. They are the result of natural selection. When
looking for adaptations in organisms, care needs to be taken that the characteristics are in fact
inheritable, and not the result of a particular individual’s life history.
Problems associated with inferring characteristics of organisms include:
o If you do not know the environment an organism lives in, then saying a
characteristic is an adaptation is just guesswork
o Sometimes, organisms gain features that are advantageous to its survival, but
are a result of the organism’s live experience. This is not an adaptation, as
adaptations are always genetically based
Case study 1: Mangroves
o Mangroves form woody plant communities in warm, shallow tidal water over more than
half of the Australian coastline.
o Mangroves are found on sheltered muddy shores and along estuaries. Depending on the
conditions and the species, they range from 2 m high shrubs to 30 m high trees.
Support and movement

Mangroves are upright woody plants. They are anchored by complex root
systems in the shifting environment of tidal mud flats. They have vertical
anchor roots to which are attached spreading cable roots. Together these
form a dense mass which helps stabilise the mud. Some mangroves support
themselves on ‘stilt’ roots that lift the plant out of the salty water.
8
Stilted Roots
o Stilt roots have numerous functions one of the most important one of
the most important one is to uphold the mangrove and ensure its
growing space.
o Another important ability of stilt roots is to allow the exchange of gas in
oxygen-poor sediments.
The arc-shaped prop roots often can be found with a huge amount of
lenticels that allow gas exchange in the oxygen-poor soils. (A lenticel is
a porous tissue consisting of cells with large intercellular spaces in the
periderm of the secondarily thickened organs and the bark of woody
stems and flowering plants. It functions as a pore, providing a pathway
for the direct exchange of gases between the internal tissues and
atmosphere through the bark, which is otherwise impermeable to gases.)
o Stilt roots bind sediments and ensure sustainable coastal protection by
sediment accumulation and counteract coastal erosion. This prevents the
tree from being uprooted.
9
Pneumatophores
Pneumatophores are erect roots that are some form of upward appendage or
extension of the underground root system. Because these roots are exposed at
least part of the day and not submerged underwater, the root system can obtain
oxygen in an otherwise anaerobic substrate.
Control of water balance
Mangroves are halophytes (salt-tolerant plants). The water available to them is salt water
with a high ion concentration. They control their salt level in three ways:
o accumulation: their cells maintain higher
than normal concentrations of cell solutes
o secretion: some mangroves have salt
glands on their leaves which actively
secrete salt
o exclusion: some mangroves use energy to excrete salt.
Control of internal temperature
o Mangrove leaves have a thick cuticle and are hard and leathery. These features help
to control water loss and prevent wilting in hot weather. In dense mangrove swamps
the thick canopy of leaves helps maintain a lower temperature in the lower layers.
10
Obtaining light
o Mangroves are the dominant plant in their community. The shape of the plant and
arrangement of leaves ensure abundant light is available for photosynthesis.
o The leaves are dark green because they are rich in chlorophyll. The leaves high on
the plant are angled and those lower down are horizontal to best capture sunlight.
Reproduction
o Mangroves have flowers and, following pollination and fertilisation, fruits
containing one seed develop. These seeds begin germination before they drop
from the parent plant. The seeds are buoyant and dispersed by the tide. Their
initial development, particularly of the root system, ensures the new plant can
rapidly anchor itself and grow rapidly once it is deposited in the mud.
11
Mangrove Identification in the Tweed:
There are 7 species of mangroves in the Tweed Estuary. The most common species are:
12
Assignment.
o Obtain photographs of the above mangroves and there leaves.
o Identify the type of water balance they use.
Case Study 2 – Kangaroos
Members of the genus Macropus are all physically very similar. Few species are solitary
and most congregate in groups or mobs.
Kangaroos are widespread across Australia. They are all grazing herbivores that feed on grasses
and herbs.
Support and movement
o Kangaroos have an internal bony skeleton. Their well-muscled hind legs are far larger
than their forelegs. Only the hind legs are used when the animal is travelling at
high speed. This method of bounding along is more efficient in terms of energy use
when compared with animals which run on all four legs.
o The long tail of the kangaroo is a useful structure. It is used as a balancing
counterweight when bounding, as an extra limb when hopping, and it helps the
kangaroo to remain upright when standing still.
Control of water balance
o Kangaroos in arid areas, such as the red kangaroo and euro, can survive for long
periods without drinking water, provided there is sufficient green plant material
available. Kangaroos reduce water loss by sweating only during exercise. When they
stop moving, sweating stops.
Control of body temperature
o When the weather is hot, euros may lick their forelimbs where the blood vessels run
close to the surface and heat is lost from the body. It is thought that the evaporation
of the saliva has a cooling effect.
13
Reproduction
o Kangaroo population numbers are controlled through reproduction. Under good
environmental conditions numbers can increase rapidly, because female
kangaroos can be almost continuously pregnant when adult. They mate again
directly after giving birth. If the mother is still suckling her newborn young, the
fertilised egg does not develop until the young leaves the pouch. This is
known as delayed implantation. At any one time a female kangaroo may have a
joey (young kangaroo) being weaned, a young one being suckled in the pouch and
an embryo in the uterus awaiting development.
o Kangaroos have the amazing ability to produce two kinds of milk at the same time.
The milk produced by the teat for the developing young in the pouch contains much
less fat than the milk produced by the teat being used by the joey outside the pouch.
o When environmental conditions are not good, such as in times of drought, young
joeys do not survive and any fertilised egg does not implant. Females do not begin
reproducing again until conditions improve.

describe and explain the short-term and long-term consequences on the ecosystem
of species competing for resources
o Competition in ecosystems is the struggle between organisms for the same
resource
o Competition can be between members of the same species or between members of
different species.
o In the short-term, competition reduces the chance of survival and restricts the
abundance of all competitors
o In the long-term, one of the competitors will eventually be more successful and
drive out or significantly reduce the numbers of other competitors
o A particular ecosystem can support only a certain number of each type of
species.
o Competition may be between members of the same species, or between members
of different species.
o Each year many more offspring are produced by most organisms than can
survive. While some young will be consumed as food by other organisms, many die
in the competition for limited resources.
14

identify the impact of humans in the ecosystem studied
o Humans can bring about rapid alterations and widespread change. Our effect is
often destructive to the original environment and its other inhabitants.
o Industrialisation and urbanisation can drastically change the natural environment
o For example in our local area
o industrialisation and urbanisation has drastically changed the natural
environment
o Sedimentation of the river occurs.
o Dredging the bay for land reclamation has also been done by humans.
Read Tweed Coast PoM document which outlines some impact and concern. Some
information from page 30 has been highlighted which indicates human impact.
Document is available on website.
Answer the question: Is human impact always negative?
15