The Costs, Benefits and Consequences of

Interactions-- Interaction between species Interaction between species

-- Interactions with the environmentInteractions with the environment

We have studied various types of biotic interaction that exist between species in an

ecosystem. Now we are going to look at these interactions again, but this time we are going

to concentrate on the COSTS, BENEFITS and CONSEQUENCES that these interactions have to

the different species

Interactions between species: SUMMARYSUMMARY

Type of I nteraction Overall Eff ect on Population Density

Competition -/ -

Predation +/ -

Parasitism +/ -

Commensalism +/ 0

Mutualism +/ +

Effects of Host Health and Environmental

Factors• In most symbiotic relationships, a STABLESTABLE

relationship exists between the two species involved

• This is perhaps most important in parasitic relationships where it is necessary that the host, although affected in a negative way by the relationship, nevertheless remains healthy enough to be able to tolerate the parasite without being affected too seriously. If it is, it may die, which would be detrimental both to the host and to the parasite

• However, this stable balance in a parasite/host relationship can be changed by either:– Health and development of the host (BIOTICBIOTIC factor)

or

– Environmental conditions (ABIOTICABIOTIC factors)

• These factors are crucial in altering the balance of an ecosystem

• In general if the health of the organism is good then it will hardly feel the effects of some of the environmental factors such as cold and wet conditions

• However if an organism is weak, then these factors will be detrimental e.g. HIV infection, overcrowding in seedlings, Botyritis infection in raspberries

Examples• People who are HIV positive and whose immune system is

therefore compromised, tend to be more at risk from opportunistic infections like pneumonia and tuberculosis than individuals whose immune system is healthy

• Seedlings which are grown in overcrowded conditions tend to grow spindly and weak and are more at risk of infections (which can pass more quickly from one individual to another in overcrowded conditions) than ones given more space. This is why gardeners 'thin' their crops of seedling plants, so that those which remain will have a better chance of growing into healthy adult plants, producing more, larger blooms etc.

• Soft fruits such as raspberries are prone to a parasitic fungal infection called Botrytis. However, how badly the fruit is affected by the parasite is dependent in part by how humid the environment is

The management of symbiotic relationships

• THEREFORE, host health and environmental conditions, such as overcrowding and humidity, can alter the balance of host/parasite interactions

• Humans can MANAGEMANAGE these factors to change the balance in favour of the host species in a variety of ways:

– by improving the quality of the host environment (e.g. reducing overcrowding) and

– by using DRUGSDRUGS, PESTICIDESPESTICIDES and HERBICIDESHERBICIDES.

Drugs

• An example of the use of drugs to alter the balance in the hosts favour is the use of anti-fungal ointment and powder in the treatment of athlete's foot - a common fungal infection in humans

• Also many farmers regularly include antibiotics in their animals' feed to prevent infection and so speed up the rate of growth of the animals. This activity is controversial, however, as it may be partly responsible for the evolution of antibiotic resistant bacteria

Pesticides

• Pesticides are chemicals used by farmers to kill insects and other animals which feed on or otherwise adversely affect crops and reduce the size of the crop yield

Herbicides• Herbicides are chemicals used by farmers to kill

other plant species which compete with the crop plants for resources such as space, light and water

• Such competition again, would reduce the growth of the crop plants and therefore also reduce the yield

• In order to prevent the crop plants being harmed by herbicides, selective herbicides are use

• These target specific types of plant - there are some which affect broad-leaved plants while leaving narrow-leaved plants unaffected while others do the opposite

Interactions with the environment

The Change of the Natural WorldThe Change of the Natural World• An organisms interaction with its environment can

change very quickly: e.g. rain, wind, sunlight, cloud cover

• Or more slowly on a monthly basis: e.g. seasons

• Longer timescales – continental drift and other geological effects, ice ages etc.

• All organisms within their lifespan have evolved ways to adjust to these changes

• However, changes can cause stress to the organism, where the condition is outside of their normal physiological range

• Despite changes in their external environment, organisms must maintain a constant internal environment : HOMEOSTASISHOMEOSTASIS

• Therefore, organisms must adapt to maintain a constant internal environment, or become restricted within a very small habitat

• Organisms have evolved a variety of BEHAVIOURALBEHAVIOURAL and PHYSIOLOGICALPHYSIOLOGICAL mechanisms to enable them to maintain homeostasis and deal with these changes :

BEHAVIOURALBEHAVIOURAL PHYSIOLOGICALPHYSIOLOGICAL

AVOIDANCEAVOIDANCE REGULATION & ADAPTATIONREGULATION & ADAPTATION

TOLERANCE & RESISTANCETOLERANCE & RESISTANCE

Behavioural Responses - AVOIDANCE

• Changes in an organism's behaviourChanges in an organism's behaviour which can be observed and which help them to survive changes in their environment– desert mammals being nocturnal and living in underground

burrows during the day to escape the heat of the desert sun

– Hibernation or migration to avoid low temperatures in winter e.g. swallows, whales, wildebeest

– Deciduous trees lose leaves in the low light intensity periods

– Sheep huddle in cold conditions

– Some animals adjust themselves to a particular position e.g. bees use wings to cool the hive

All avoidance usually involves a considerable investment of energy from the individuals concerned, but is beneficial

in the long-term

Physiological Responses

• Changes in the way an organism's body Changes in the way an organism's body functionsfunctions to enable it to survive in changing circumstances

• Many of these responses enable an organism to show a certain tolerance to the changes in its environment

Examples: – The camel's body tissues are very tolerant to dehydration -

it can lose up to 30% of its body water and still survive. In humans a 10% water loss causes kidney failure

– We shiver, hairs stand up, go pale etc in response to cold

– Wilting in plants

– Growing a thick coat of fur

• Information on a physical response to an environmental change can be turned into a RESPONSERESPONSE CURVECURVE

• This allows you to identify the optimum conditions and the range in which the organism will survive

• Response curves vary with SPECIESSPECIES, , STAGE OF LIFESTAGE OF LIFE and HEALTHHEALTH of organism when exposed to the stress

• It also varies with the TYPETYPE and INTENSITYINTENSITY of the stressful situation

Response curve

Although organisms can tolerate a range of external environmental changes, they function most efficiently at certain optimum

environmental conditions. An organism's responses to a changing environmental factor can be studied in the laboratory and a tolerance,

or performance, curve can be produced

Adaptations in Plants • There are two types of plant that have

adapted to controlling water concentrations in different habitats – XEROPHYTESXEROPHYTES

– HYDROPHYTESHYDROPHYTES

• Xerophytes are adapted to habitats where transpiration rates are high. These could be hot dry habitats which lack soil water (desert) or exposed windy habitats (moorland)

• Hydrophytes are adapted to living in submerged or partly submerged conditions in aquatic habitats

XEROPHYTES

• Sunken stomatal pits• Succulent tissues

• Leaf reduced to spines

• Long roots

• Stem with rounded shape

• Reversed stomatal rhythm

• Thick, waxy cuticle

• Rolled leaves

• Hairs

HYDROPHYTES• Aquatic plants have a problem

of obtaining oxygen

• The hydrophyte overcomes this problem by having air filled cavities

• Oxygen formed in photosynthesis is held within these air spaces

• Reduction of xylem is a further adaptation

• Water provides support for the plant, therefore the use of xylem in support is not required

• Any xylem found is located in a central column for maximum flexibility

Homeostasis• Process of maintaining constant internal environment

• Maintains INTRAcellular and EXTRAcellular fluids at a relatively constant ionic and osmotic compositions despite fluctuations in external conditions

• Abiotic factors e.g. water, light, temp., soil nutrients etc largely determine what organisms live there, homeostasis has enabled organisms to inhabit a diverse range of environments and to exist within narrow physiochemical ranges

• When this external environment CHANGESCHANGES there are 2 basic patterns of response:– CONFORMATIONCONFORMATION : change in internal environment with the external

environment– REGULATION : REGULATION : maintenance of internal environment regardless of

changes in the external environment

Conformation• Where internal variables fluctuate DIRECTLYDIRECTLY with the

external environment• Survival depends on the cellular resistance to damage

Osmoconformers : Marine invertebrates, such as crabs, shrimp and jellyfish.They are isosmotic and their body fluids are isotonic with their environment (conc. of solutes in the extracellular fluids is equal to that of the surrounding seawater). Therefore, no osmotic gradient exists, so no water enters or leaves the body of the organism. Osmoconformers do not alter their internal solute concentration

Poikilotherms : Animals whose body temperature varies with the surrounding environment. These are usually ectotherms (cold-blooded) that absorb heat from the surrounding environment e.g. snakes, lizards and marine fish

Regulation• Where the internal variables are maintained at levels

DIFFERENTDIFFERENT from their environment. This requires significant ENERGY COSTENERGY COST

Osmoregulators : e.g. freshwater organisms, terrestrial animals, body fluids are not isotonic with the environment and so need to use energy to regulate their internal osmolarity by excreting excess water or taking in additional water.They use a variety of osmoregulatory mechanisms to do this.

In hypotonic environments : they GAIN water by osmosis

In hypertonic environments : they LOSE water by osmosis

Homeotherms : are animals that maintain a constant body temperature. These are usually endotherms (warm-blooded) that derive heat from metabolism e.g. mammals, insects, birds

Habitat occupation of conformers &

regulators• CONFORMERSCONFORMERS can only survive in habitats

which provide their particular environmental conditions, although they conserve energy by not regulating

• REGULATORSREGULATORS use a lot of energy to carry out their homeostatic activities. However, the huge advantage they have is that they can colonise a range of different habitats since they can maintain their internal environment - thus can exploit habitats which conformers cannot!

Dormancy• Period in the life of an organism

during which the metabolic activity is greatly reduced

• This allows the organism to survive:– Bad environmental conditionsBad environmental conditions

– Severe resource shortageSevere resource shortage

• It can also allow for dispersal or internal change

Predictive vs Consequential

• 2 types of dormancy exist:

– PREDICTIVEPREDICTIVE : occurs in advance of adverse conditions e.g. hibernation

– CONSEQUENTIALCONSEQUENTIAL : occurs in response to prevailing conditions e.g. seed dormancy due to draught

Dormancy forms• RESTING SPORESRESTING SPORES : found in a wide diversity of forms.

Temperature and draught resistant stages exist in bacteria, fungi, plants and lower animals

• HIBERNATIONHIBERNATION – a period of inactivity in mammals associated with animals physiological changes resulting in a lowering of metabolic rate to conserve energy during periods of environmental extremes e.g. polar bear, dormice

• AESTIVATIONAESTIVATION – a period of inactivity associated with hot, dry periods [usually summer] during which the organism remains in a state of torpor with reduced metabolic rate e.g. lung fish

• DIAPAUSEDIAPAUSE – a form of dormancy typically found at a specific stage in an insect life history and involving complete cessation of growth and development together with suspended metabolism. This is controlled by hormones

AESTIVATION : ExampleAESTIVATION : Example

• African and South American lungfish are capable of surviving seasonal desiccationseasonal desiccation of habitats by burrowing into mud and aestivating throughout the dry season

• Changes in physiology allow the lungfish to slow its metabolism to greater than 1/60th1/60th of the normal metabolic rate, and protein waste is converted from ammonia, to less-toxic urea, (normally, lungfish excrete nitrogenous waste as ammonia directly into the water)