Coping with dangers

							               Alford Academy




                Higher Biology

     Unit 2: Genetics and Adaptation




               Obtaining Food
               Chapters 24-25

Name: __________________ Teacher: ________________
                       -1-
                            Obtaining Food In Animals

Animals move! One of the main reasons for this is because they constantly
require an external source of food. Obtaining food is one of the most important
survival tasks for animals and, not surprisingly, they have evolved some special
behavioural adaptations.

The aim of this unit is to look at the behaviour strategies employed by animals
which maximise their energy gain and minimises energy loss.

Chemotaxis in Planaria

When animals go foraging for food they show distinct behaviour patterns to gain
the maximum energy from the food. The experiment shown in figure 24.2 on page
189 (old), page 205 (new) in Torrance shows Planaria activity in the presence of
food i.e. they have chemoreceptors to help them forage for food.

Complete AYK question 1 page 197 (old), page 214 (new) below:
     Features of experimental design                    Reason




              Foraging Behaviour and Search Patterns in Animals

Foraging is the act of obtaining food by an animal.

The energy gain from the food must be greater than the energy used up searching
and consuming the food.




                                         2
                             Examples of Search Patterns
 Bees

 Bees perform the so called “waggle dance”. This dance indicates not only the
 distance and direction of a good nectar source but the volume of food at that
 source.
            10
                                                                 Calm, sunny day
Number       8                                                   Calm, dull day
of bees
             6
visiting
a patch      4
of
             2
flowers
                  10    12     14    16   18      20   22   24
                                Time of day

 1) On which type of day did most bees visit the flower?



 2) On the sunny day, at what time did most bees visit the flower?



 3) Suggest a reason for most bees visiting the flower at this time.




                                    Foraging in Ants

 Ants go backwards and forwards over a piece of ground which increases the
 chance of finding food. Once food has been found the ants then leave scent
 marks for other ants to follow.



 Read Torrance page 190 (old), 206 (new) and answer AYK question 2 on page
 197(old), pages 214-215 (new).




                                              3
                                 Higher Animals

Higher animals have a more complex search pattern which is not purely instinctive
but based on learning. Many show sophisticated physiological adaptations e.g.
ultrasonics in bats to locate prey, speed in the cheetah and stealth in the tiger.

                         Economics of Foraging Behaviour
Foraging animals must:

 Move around in a way that minimises energy expended
 Select prey species that maximise the energy gained.

It would be inefficient for animals to forage for food in a way that expended
more energy than the energy value of the food found.

Shore Crabs choose the mussels that will give them the highest rate of energy
return. Very large mussels take so long to open that it is not economic in terms of
energy gained. Very small mussels are easy to open but contain very little flesh.
There is an optimum size of mussel which gives maximum energy gain for the
minimum time spent opening the shell.
Energy Gain                           Energy Expended
From Food                             Searching
                                      Catching
                                      Handling
                                      Eating
                                      Avoiding Predators
Foraging strategy must be organised for maximum energy gain.

                   Factors Affecting Foraging Strategy
 Energy Expenditure – food eaten must give more energy than the energy used
  up in the search and the catch.

 Richness of Food Supply – Organism can be choosier about food in an
  ecosystem where food is more abundant.

 Choice of prey size – e.g. mussels

 Risk of Predation – In some cases it is economical for an herbivore to settle for
  food available in a poorer ecosystem if foraging in a food-rich area exposes it
  unduly to risk of attack by predators.

Now answer TYK questions 1-3 on pages 191-192 (old), page 208 (new)
                                         4
                                    Competition

There are two types of competition:

      Interspecific competition (competition between species e.g. species of
       paramecium)
      Intraspecific competition (competition within a species)

Read Torrance pages 192-194 (old), pages 208-210 (new).

Complete the following passage on competition using the following words; the
same species, food and shelter, different species, ecological niches

In    animals   interspecific   competition   arises   when   two   organisms   of

_____________ ________ occupy the same _______________ _________.

An organism’s niche is its position in an ecosystem. This is determined mainly by

its feeding habits.

The animals will compete with each other for resources such as           and

__________.

When two organisms are competing for a resource that is in limited supply the
competition will become fierce.

Intraspecific competition arises when overcrowding occurs within a population of

          _________ __________. This will result in behavioral responses such

as migration and aggression.

Question

Explain why intraspecific competition is more intense than interspecific
competition.



Now answer TYK questions 1 & 2 page 196 (old), page 214 (new).



       Consider the graphs of populations of Paramecium on the next page.


                                         5
         Population growth of two species of Paramecium grown in flasks.




                 Paramecium Aurelia              Paramecium caudatum

  1) What type of competition is involved in the situation shown above? Why?



2) Give 3 resources that the two organisms are competing for.



The ‘competitive exclusion principal’ has happened in squirrels and trout. In
order to reduce competition happening between animals occupying the same niche
animals sometimes reach a compromise by eating different foods or nesting in
different habitats. This is shown in cormorants where 2 species feed on
different fish.
                             Territorial Behaviour
A territory is an area held and defended by an organism or group of organisms
against organisms of the same species or different species.

In order to reduce intraspecific competition some animals establish territories.
An animal’s total range is the total area covered in its lifetime. However in that
range the animal establishes a smaller area called its territory. Its territory
contains enough food for it and it’s young.
Territory holders are solitary and each enjoys complete dominance over its
territory. The size of territory is critical, for if it is too large it will be too
difficult to defend. However it must be large enough to support an animal and it’s
young.


                                         6
Birds of prey and large carnivores have territories several square miles in area in
order to provide all their food requirements. Herring gulls and penguins however
have territories of only a few square metres since they move out of their
territories to feed and use them for breeding purposes only. A robin’s territory
might be the size of a small garden. The size of territory is dependent on the
volume of food available in the territory. The advantage of a territory is that it
provides a safe place to breed where there will be enough food for the young.

The function of territorial behaviour is to ensure that each mating pair and
their offspring are adequately spaced to receive a share of the available
resources.

1) Why is a territory beneficial to an animal?




2) What are the costs to the animal in having a defined territory?



3) What happens if the territory is too small?




4) What happens if the territory is too big?




5) What would you expect to happen to the size of territory if the quality and
   quantity of food were increased?



6) How will an animal be aware that it is entering another animal’s territory?




Now answer
      TYK question 3 page 196 (old), page 214 (new)
      AYK questions 4 & 5 page 198 (old), page 215-216 (new).


                                         7
                                The Social Group

In the wild, many animals, such as monkeys, live in groups. There are many obvious
advantages to living in a group; many eyes, many “hands” and many bodies that will
make tasks such as catching prey easier to accomplish. A lone wild dog could not
hope to catch a large deer on its own.

But living together creates more competition. You can see this when you feed the
ducks or the pigeons. Squabbles arise, but fighting is rare. This is because
certain social strategies are being employed to reduce conflict.

                              Dominance Hierarchy

Many large animals live in social groups. Within these groups members react to
social signals given out by other animals in the group. We talk about a ‘pecking
order’ in birds where the first hatched chick will be the dominant member of the
group and will out compete all the others for food. Down the order will be the
second in the hierarchy which will out compete all the other birds except the
first and so on.

In mammals the dominant individual has rights of choice of food, sleeping
arrangements and mates. The others accept the status by showing subordinate
behaviour by e.g. dogs lying on their backs.

The advantage of a dominance hierarchy is that it increases the chances of
survival of the species by:

     Minimizing real aggression
     Reducing conflict within a group
     Guaranteeing leadership
     Allowing the stronger animals to pass on their genes
     Cooperative hunting and avoiding predation
     Reduces energy expended in competition

                             Cooperative Hunting
This is when animals within a social group work together to catch and share food.

Advantages
   A group of animals can catch prey that an individual could not

   It increases the chances of successfully catching prey

   Weaker individuals obtain food
                                         8
Once the prey is killed, the dominant animal receives first choice of the dead
prey and the subordinate animals must wait for what is left.

Read about cooperative hunting on page 196 (old), pages 213- 214 (new) in
Torrance.

Now complete the following table on the next page.
     Name of
                     Prey        Method of capture         Typical behaviour
      animal


       Lion




     Wild dog




                            Obtaining Food in Plants
Animals move about in order to obtain food. Plants are static and move very little
(sessile). To obtain food, plants must either: -

   Make their own food by photosynthesis

   Attract food to them (insectivorous plants attract, trap and digest insects)

                                   Competition

Plants compete for light, water and minerals. As with animals there are 2 types of
competition. As with animals, plants compete against each other (intra-specific)
and against other species (inter-specific) for nutrition.

Farmers use a drilling machine to space plants out to prevent competition.
Interspecific competition is usually less severe. Plants occupying the same
habitat may have different growth patterns see figure 25.3 on page 201 (old),
figure 25.4 on page 220 (new).

However some plants may become dominant at the expense of others e.g. those
that cut out light, or produce an acid soil e.g. a coniferous woodland. Others may
produce toxic substances to inhibit the growth of others.
                                        9
                               Competition for Light

Plants photosynthesis during the daylight. The rate is determined by light
intensity. It increases to a maximum at midday, when light is brightest, then
decreases with decreasing light intensity.
Plants continually at more or less a constant rate, carry out Respiration.
   X = Compensation Point                    Y = Compensation Period




Compensation Point is the light level at which the rate of photosynthesis is equal
to the rate of respiration.
Compensation Point definitions: -
   Varies depending on the species
   Is when food made = food used
   Is when carbon dioxide uptake = carbon dioxide output
   Is when total energy build up = total energy loss
Compensation Period is the time taken to reach the compensation point after
being in darkness.
                           Sun and Shade Plants
Plants which grow in brightly illuminated habitats are called sun plants e.g.
deciduous trees such as Oak and Beech.
Plants which grow in dimly lit habitats are called shade plants e.g. crocus and
bluebell.
Sun plants
These require high light intensities for photosynthesis. To ensure that maximum
light intensity is obtained, sun plants have the following adaptations: -
   Sturdy, erect stems which make the plant tall and able to reach the sunlight
   Leaves arranged in a mosaic pattern that avoids overlapping and shading of
    leaves.
                                         10
Sun Plants: -
      Have a higher compensation point
      Have a longer compensation period
      Require higher light levels to show a net energy gain.

Shade Plants
These are able to carry out photosynthesis at low light intensities. This ensures
their survival in shady environments. These kinds of plant often inhabit woodland
floors.
Shade Plants:-
   Have a lower compensation point
   Have a shorter compensation period
   Even at low light levels, can show a net energy gain.
Now answer TYK questions 1-3 & 5 page 205 (old), page 224 (new)


                               Species Diversity
The more species there are in habitat, the more diverse is the habitat. A diverse
habitat is desirable because the more plant species there are: -

   The more likely there will be plants of high nutritional value for grazing
    animals
   The more animal species can be supported since each will have its preferred
    food plant
   The more likely it is that there will be plants present which are beneficial to
    the soil, e.g. nitrogen-fixing plants such as clover.
Low species diversity can result in a reduction of grazing animals and soil
nutrients.
Grazing is the eating of plants by herbivores.

Species diversity can be affected by overgrazing. It results in too many species
being eaten and a reduction in diversity.
Overgrazing of heather moorland results in it reverting to bracken and rough
pasture.

Undergrazing allows more dominant plants to take over, swamping the less
competitive.
Farmers must continually assess the species diversity of their pasture in order to
adjust the level of grazing so that diversity can be maintained.
                                        11
Now answer
        TYK question 4 page 205 (old), page 224 (new)
        AYK questions 5-7 & 9 pages 205-208 (old), pages 224-228 (new).

                                  Obtaining Food

                           Activity                               I can find    I can
                                                                  this in my   do this
                                                                    notes
Define the terms ‘Foraging’ and ‘Foraging optimally’
State that factors which determine foraging success are:
time involved (searching, pursuing, handling); prey density;
predator density; size of prey
Describe how each of the above factors affects the foraging
behaviour & foraging success of an animal
Define the terms ‘intraspecific competition’ and ‘interspecific
competition’
Explain what is meant by the terms ‘territorial behaviour’
State the advantages & disadvantages of territoriality
Briefly describe how a named animal defends it’s territory
Describe with examples the term ‘co-operative hunting’
Describe the advantages & disadvantages to the individual of
this type of behaviour
Describe how foraging in large groups benefits herbivores
Describe the organisation of a group of social animals and
refer to social signals within the group
State that plants compete with each other for light, water
and soil minerals
State what is meant by the term ‘compensation point’
State that at light intensities greater than the C.P. plants
make excess food for use in growth & reproduction
State that in order to cope with competition for light plants
can have a lower C.P. or a higher C.P.
State that grazing can affect the diversity of plant species
Describe the effect low intensity grazing has on plant
diversity
Describe effect intensive grazing has on plant diversity


                                         12