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Ecology 1

BIO1006

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Ecology: the interactions that determine the distribution & abundance of organisms
Species: where organisms are able to breed and produce fertile offspring
Natural selection: variation between species (and within species) depends on environmental
conditions and characteristics of an individual
Species identification: basis of morphology (appearance), behaviour, cell biology and biochemistry
Population: a group of individuals of one species under investigation
Subpopulation: smaller groups from a large population
Metapopulational: groups made up of individuals from different subpopulations
Community: all of the species living in one area of the natural world
Ecosystem: the biological community together with its physical environment
Species Naming
EG: Musca Domestica L
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Soil Structure
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Both land & water animals are affected by the soil
Aquatic organisms have their distribution affected by particle size
Greatest effect on soil inhabitants:
o Seeds & roots
o Soil animals EG worms

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Biotic Factors
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Prey/resources
o Autotrophic organisms: green plants & bacteria (inorganic resources)
 Radiation
 Carbon dioxide
 Water
 Minerals
o Heterotrophic organisms: Animals & decomposers (organic resources)
 Decomposes: dead bodies/waste
 Parasites: consume organisms
 Predators: consume organisms

Competition
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An interaction in which one organisms utilises a resource which might have been used by
another
o Intraspecific competition
 Same species
o Interspecific
 Different species
 Live in a community
 May have similar growth & mating needs
 If demand exceeds what is available, they will compete for resources
 Effects are dependent on density
 Could end up coexisting or one species excluded

Ecological Niche
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The requirements for abiotic conditions
or resources
o Individuals of the same species
have very similar niches
o Individuals of different species
usually have distinct niches
o If two species’ niches overlap,
you may get interspecific
competition

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Spatial & Temporal Variation in Temperature

Latitudinal and seasonal temperature variation due to the angle at which the Earth is tilted
o EG temperature isotherms at certain times of the year & altitude up mountains create
temperature variations

Microclimates
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Bottom of a valley may be 31°C cooler at night

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Cracks in a south facing tree surface may be 30°C at hottest point in day compared to cooler
temperatures of the opposite side
The tops and bottoms of tree canopies may reach different minimum temperatures over night

Effects on Organisms & Their Responses
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Temporal variation
o Tolerance: EG perennial plants
o Dormancy: annual plants/animals
o Movement: migratory animals EG Knot
Spatial variation
o Across climatic zones
 Affects present species EG tropical forests/arctic tundra
 Most marked for species with low dispersal power
o Within a region
 Wild madder: correlates to a 4
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Plant material has a high carbon content C:W is 40:1
Bacteria, fungi & animals is lower C:W is 10:1

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Plants are rich in carbon but poor in protein
o This carbon is burnt off as carbon dioxide which is rich in energy
Herbivores waste products which consume plants are carbon rich compounds
o Carbon dioxide
o Fibre
Most herbivore are limited by nitrogen
Only a few herbivores have celluloses

Organisms with Celluloses
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many fungi, some bacteria and a few protozoa have celluloses
some bacteria are found in symbiotic association with herbivores
o EG ruminants in the gut
Microorganisms are the first detritivores to colonise plant detritus, animal detritivores follow
later

Animals as Food
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In nutritional terms herbivores & carnivores have similar body composition
Animal tissues:
o No structural carbohydrate or fibre
o Rich in lipids and protein
Main excretion is nitrogenous
Animals may be generalists
o Feeding on a range of foods
Some may specialise on a food source
o May attack certain parts of prey
o Target several or just one prey species
Carnivores don’t have digestion problems but have to find, catch and handle their prey

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The Chemical Environment II: Pollutants

Pollutant: a substance that contaminates, chemical produced from industrial waste
Effects of Pollutants
 Sulphur
o Deposition
from
the
atmosphere has maintained
input to agricultural land
o As pollution levels decrease
the rate of deposition decreases
o Some plants need sulphur to
grow and so additional has to be
applied to crops
 Zinc

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Found around mines and from industrial processes
Can reach fatal levels for organisms in polluted areas

Direct Effects
Natural Selection
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Pollutants having a direct effect will exert selection pressure
Tolerant individuals survive and non-tolerant individuals may die out because they’re unable
to survive the conditions
This could ultimately result in local extinction
The selection pressure will lead to optimum genotype selection
Ecotypes are a genetically determined local match between organisms and their environment
within species

Tropic Accumulation
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The pollutant is retained after consumption and so accumulates
Consumption in the next trophic level leads to further cycles of concentration
o Called BIOMAGNIFICATION
o EG Insecticides in Clear Lake, California
 These accumulated in the lake which was then consumed by plankton, these
plankton are then consumed by fish
 The Insecticides then move up the food chain, gradually increasing in size
 Results in birds producing weak egg shells & are unable to reproduce
successfully
o Fluoride on Insects
 Insects are contaminated with fluoride
 Predatory species, EG spiders, have higher fluoride concentration than
herbivores EG aphids

Indirect Effects
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In Industrial areas trees were blackened by soot
Normally Peppered Moths had a pale colour with black peppered effect, these were
eventually replaced by much darker moths
Selection pressure due to bird predation caused the paler moths to decrease in numbers as
they were much easier to detect
After the Clean Air Act, the cleanliness of the air increased and trees became cleaner, this
meant that the lighter coloured moths returned

Acid Rain
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Sulphur and nitrogen oxides from the burning of fossil fuels causes acid deposition in the
atmosphere
This dissolves in the clouds producing acid rain which affects the pH of rain and water bodies
This then affects the organisms in water bodies
o EG diatoms

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Insect Herbivores
Carnivores

Herbivores

Plants

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There’s no strong evidence for removal of control from above (predators)
There is a good evidence for release of control from below (plants)
Plants that are stressed by pollutants provide a better food source as they have a high nitrogen
content
There is strong evidence for a direct uptake by plants of nitrate or ammonia from pollutants

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The Biotic Environment: Conspecifics

Reproduction

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Species with sexual reproduction, which cross fertilise, will need other individuals to
reproduce
If there is a low population density the animal may be unable to find a mate
A high population density could mean that there is an increased chance of finding a mate but
also an increased chance of competition for food, mates & between males etc
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The mortality constant
- The number of animals dying & surviving increases
- The proportion dying stays the same
- There is no competition
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Mortality Increased further
- There is intense competition
- Density is dependent on the mortality
- Overcompensates

When birth rate = death rate
The population is said to be at carrying capacity (K)

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Territoriality
 This is a result of interference competition
 Animals without a territory will make little or no contribution to the future generations
 Territoriality is linked to the regulation of a population
o EG Oyster catchers

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Mutualism

Mutualism is the associations between pairs of species that bring mutual benefit
Individuals in each population show greater:
o Survival
o Growth
o Population
Types of benefit:
o One of the party receives food
o Protection from enemies
o Provision of favourable environment
o Pollination and seen dispersal
Each partner is acting selfishly
Mutualism may be
o Facultative
o Obligate for one and facultative for the other
o Obligate for both
EG Ant – Plant
o Ant gains food and shelter
o Plant gains herbivore protection and competition is reduced
EG Animal guts and inhabitants
o Animal gains digestive resources
o Contain digestive enzymes that break down proteins etc
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The
tropical region is characterised by more specialist fruit or insect
feeders
Altitude:
 Species richness decreases with
altitude
 Predation and productivity
explanations might be relevant
 Climate stability is less likely to
be relevant

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High altitude communities might be effected by islandness i
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species-area effect
Succession:
 Species richness increases with successional age
 It involves colonisation suggesting the early stages are not saturated
with species
 The colonisation process also demonstrates a cascade effect: the
early colonisers provide resources for later arrivals

Applied Ecology

Pest Management
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A pest is a species causing direct or indirect
damage to man
They’re usually r selected species with rapid
reproduction
The aim of pest control is not eradication, but
management so that losses are less than the
costs of control
Economic injury level: the point where it becomes cost effective
Methods of managing:
o Chemical pesticides
 Broad spectrum EG DDT
 Specific EG insect growth regulators
o Biological control
 EG cottony cushion scale insect in Californian citrus
 The Vedalia beetle is imported to feed on it
 The population is reduced to below the economic injury level
 Klamath weed in the US rangeland
 A beetle, the Chrysoline quadrigemina was imported to feed on it
 The plant become restricted to shaded hedgerows
o The beetle is more active in the sun and the damage plant is
susceptible to drought
o Cultural control
 Cultivation
 Host-plant resistance
Problems
o Natural enemies are also destroyed, if they control abundance
 The target pest may have a sudden resurgence EG aphids
 There may be secondary pest outbreaks because you have wiped out their
natural enemy EG mites
o Organisms can become resistant to control methods by natural selection
o Effects on non-target organisms
 EG trophic accumulation in clear lake
o Speed of control
 You need an early warning by forecasting using population modules

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Extent of control
 Effects of market forces
Decreased productivity in a community may be linked to a decrease in numbers of species

Harvesting
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Harvesting/fishing/shooting/culling
o EG grass/timber/fish/whales/deer
Ideally should not overexploit or underexploit the population
Harvesting is usually based on commercial considerations
At low population densities, recruitment is low
At high population densities you get intraspecific competition and low recruitment
The most frequent harvests are at intermediate population densities
Harvest is done when the recruitment rate is maximal, which gives the maximum sustainable
yield, this assumes all organisms are the same ages

Environmental Protection
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This aims to understand and control human’s impact on the environment
You need to be able to evaluate:
o The environment before the event
o The scale of the impact
o The rate and extent of recovery
Evaluation of the environment
o Need an objective survey that’s quantifiable
 Looking at the species number/diversity/rarity
o Need an assessment of how unique the community is
Scale of the impact
o Is the community being destroyed or damaged
o What area is affected and will the recolonization in islands be affected
o Restoration activities may affect the rate and direction of the recovery
Rate and extent of the recovery
o May be based on experience, EG open-cast mining
o May be based on conjecture EG global environment change
o The rate of recovery can be increased with skilled management

Conservation
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Aims to prevent species or communities becoming extinct regionally or globally
Species at risk are usually rare and there are different types of rarity
o They may have a narrow geographical range
o A narrow habitat range
o Populations are low densities
Species may be pushed towards extinction by various forces
o Deterministic: the habitat becomes less able to support the species
o Stochastic: the more random effects of the environment
Causes of rarity:
o Rare habitable areas
o Short-lived habitable areas
o Small habitable areas

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o Isolated habitable areas
o There may be competitors or natural enemies
o The resources are sparse
o Genetic variation lacking
Species-area relationships (island biogeography) are useful in conservation, for example the
planning of the size of nature reserves
If an area that is part of a larger community is turned into a reserve, there will be fewer species
Larger reserves should support more species due to a wider range of food sources, habitats
etc

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