RosieYear 11IB

Ecology and Evolution

Ecology and evolution: TOPIC 5

5.1.1Define species, habitat, population, community, ecosystem and ecology. Species: A group of organisms that can interbreed and produce fertile offspring

Habitat: The environment in which a species normally lives or location of the living organism

Population: A group of organisms of the same species tat live in the same area at the same time

Community: A group or populations living and interacting with each other in an area.

Ecosystem: A community and it’s abiotic environment

Ecology: The study of relationships between living organism and between living organisms and their environment.

Autotroph: An organism that synthesizes it’s organic molecules from simple inorganic substances.

Heterotroph: An organism that obtains organic molecules from other organisms

Consumer: An organism that ingest other organic matter that is living or recently killed

Saprotroph: An organism that obtains organic molecules from other organisms.

Detritivore: An organism that ingest non-living organic matter

5.1.2 Distinguish between autotroph and heterotroph.

Distinguish means to give the differences between two or more different items.

5.1.3 Distinguish between consumers, detritivores and saprotrophs.

Distinguish means to give the differences between two or more different items.

 

E.g. Consumer cow, eats grass Detritivore- earthworm, eats soil organic matter, not living Saprophytes- fungi ( extra cellular digestion) secrets digestive enzymes, abosrobs

nutrients for growth.

5.1.4 Describe what is meant by a food chain, giving three examples, each with at least three linkages (four organisms)

A food chain shows the linear feeding relationships between species in a community

The arrows represent the transfer of energy and matter as one organism is eaten by another (arrows point in the direction of energy flow)

The first organism in the sequence is the producer, followed by consumers (1°, 2°, 3°, etc.)

Examples of Food Cha

ins

5.1.5 Describe what is meant by a food web

A food web is a diagram that shows how food chains are linked together into more complex feeding relationships within a community

There can be more than one producer in a food web, and consumers can occupy multiple positions (trophic levels) 

5.1.6 Define trophic level  

position it occupies in a food chain. Producers always occupy the first trophic level, while saprotrophs would generally

occupy the ultimate trophic level of a given food chain or food web The trophic levels in a community are:

5.1.7 deduce the trophic levels of organisms in a food web and food chain

The trophic level of an organism can be determined by counting the number of feeding relationships preceding it  and adding one (producer always first) 

Trophic Level = Number of arrows (in sequence) before organism + 1 In food webs, a single organism may occupy multiple trophic levels

5.1.8 construct a food web containing up to 10 organisms, using appropriate information

Hint:  When constructing a food web, always try to position an organism relative to its highest trophic level (to keep all arrows pointing in same direction)

Food web (trophic levels in red)

5.1.9 State that light is the initial energy source for almost all communities

▪ All green plants, and some bacteria, are photo-autotrophic - they use light as a source of energy for synthesizing organic molecules

▪ This makes light the initial source of energy for almost all communities ▪ Some bacteria are chemo-autotrophic and use energy derived from chemical processes

(e.g. nitrogen-fixating bacteria)

5.1.10 explain the energy flow in a food chain

▪ Energy enters most communities as light, where it is absorbed by autotrophs (e.g. plants) and converted into chemical energy via photosynthesis

▪ Energy then gets passed to the primary consumer (herbivore) when they eat the plant, and then gets passed to successive consumers (carnivores) as they are eaten in turn

▪ Only ~10% of energy is passed from one trophic level to the next, the rest is lost ▪ Because ~90% of energy is lost between trophic levels, the number of trophic levels are

limited as energy flow is reduced at higher levels

Summary of Energy Flow in a Food Chain

5.1.11 State that energy transformations are never 100% efficient

▪ When energy transformations take place in living organisms the process is never 100% efficient

▪ Typically, energy transformations in living things are ~10% efficient, with about 90% of the energy lost between trophic levels

▪ This energy may be lost as heat, be used up during cellular respiration, be excreted in feces or remain unconsumed as the uneaten part of food

5.1.12 Explain the reason for the shape of pyramids of energy

pe

▪ A pyramid of energy is a graphical representation of the amount of energy of each tropic level in a food chain

▪ They are expressed in units of energy per area per time (e.g. kJ m2 year -1)▪ Pyramids of energy will never appear inverted as some of the energy stored in one

source is always lost when transferred to the next source▪ This is an application of the second law of thermodynamics▪ Each level of the pyramid of energy should be approximately one tenth the size of the

level preceding it, as energy transformations are ~10% efficient

5.1.13 Explain that energy enters and leaves ecosystems, but nutrients must be recycled

▪ The movement of energy and matter through ecosystems are related because both occur by the transfer of substances through feeding relationships

▪ However, energy cannot be recycled and an ecosystem must be powered by a continuous influx of new energy from an external source (e.g the sun)

▪ Nutrients refer to material required by an organism, and are constantly being recycled within an ecosystem as food (either living or dead)

▪ The autotrophic activities of the producers (e.g. plants) produce organic materials from inorganic sources, which are then fed on by the consumers

▪ When heterotrophic organisms die, these inorganic nutrients are returned to the soil to be reused by the plants (as fertiliser)

▪ Thus energy flows through ecosystems, while nutrients cycle within them

5.1.14 State that saprotrophic bacteria and fungi (decomposers) recycle nutrients

▪ In order for organisms to grow and reproduce, they need a supply of the elements of which they are made 

▪ The saprotrophic activity of decomposers (certain bacteria and fungi), free inorganic materials from the dead bodies and waste products of organisms, ensuring a continual supply of raw materials for the producers (which can then be ingested by consumers)

Thus saprotrophic bacteria and fungi play a vital role in recycling nutrients within an ecosystem  5.2.1  Draw and label a diagram of the carbon cycle to show the processes involved

There are four main 'pools' of carbon in the environment:

• Atmosphere                        • Biosphere                        • Sediments                   • Ocean

There are a number of processes by which carbon can be cycled between these pools:

▪ Photosynthesis:  Atmospheric carbon dioxide is removed and fixed as organic compounds (e.g. sugars)

▪ Feeding:  In which organic carbon is moved from one trophic level to the next in a food chain

▪ Respiration:  All organisms (including plants) metabolise organic compounds for energy, releasing carbon dioxide as a by-product

▪ Fossilization:  In which carbon from partially decomposed dead organisms becomes trapped in sediment as coal, oil and gas (fossil fuels) 

▪ Combustion:  During the burning of fossil fuels and biomass▪ In oceans, carbon can be reversibly trapped and stored as limestone (storage happens

more readily at low temperatures)

The Carbon Cycle

5.2.2  Analyse the changes in concentration of atmospheric carbon dioxide using historical records

Recent Trends:

▪ Atmospheric carbon dioxide concentrations have been measured at the Mauna Loa atmospheric observatory in Hawaii from 1958 and has since been measured at a number of different locations globally

▪ The data shows that there is an annual cycle in CO2 concentrations which may be attributable to seasonal factors, but when data from the two hemispheres is incorporated, it suggests that atmospheric CO2 levels have risen steadily in the past 30 years

Long Term Estimates:

▪ Carbon dioxide concentration changes over a long period of time have been determined by a variety of sources, including analysing the gases trapped in ice (and thus providing a historical snapshot of atmospheric concentrations)

▪ Data taken from the Vostok ice core in Antarctica shows that fluctuating cycles of CO2 concentrations over thousands of years appear to correlate with global warm ages and ice ages

▪ It is compelling to note that CO2 levels appear to be currently higher than at any time in the last 400,000 years

Recent and Long-term Changes in Carbon Dioxide Concentration

                   Mauna Loa CO2 Data  (last 50 years)                                                     Vostok Ice Core Data - CO2 vs Temperature (last 400,000 years)    

   

5.2.3  Explain the relationship between the rises in concentrations of atmospheric carbon dioxide, methane and oxides of nitrogen and the enhanced greenhouse effect

The greenhouse effect is a natural process whereby the earth's atmosphere behaves like a greenhouse to create the moderate temperatures to which life on earth has adapted (without the greenhouse effect, temperatures would drop significantly every night)

▪ The incoming radiation from the sun is short-wave ultraviolet and visible radiation▪ Some of this radiation is reflected by the earth's surface back into space as long-

wave infrared radiation▪ Greenhouse gases absorb this infrared radiation and re-reflect it back to the

earth as heat, resulting in increased temperatures (the greenhouse effect)

The Greenhouse Effect

The enhanced greenhouse effect refers to the suggested link between the increase in greenhouse gas emissions by man and changes in global temperatures and climate conditions

The main greenhouse gases are water vapour, carbon dioxide (CO2), methane (CH4) and oxides of nitrogen (e.g. NO2)

While these gases occur naturally, man is increasing greenhouse gas emissions via a number of processes, including:

• Deforestation (less trees)                       • Industrialisation (more combustion)           • Increased farming / agriculture (more methane)

With increases in greenhous gas emission, it is thought that the atmospheric temperature may increase and threaten the viability of certain ecosystems, although this link is still being debated

5.2.4  Outline the precautionary principle

The precautionary principle states that when a human-induced activity raises a significant threat of harm to the environment or human health, then precautionary measures should be taken even if there is no scientific consensus regarding cause and effect

▪ Because the global climate is a complex phenomena with many emergent properties, and is based on time frames well beyond human lifespans, it is arguably impossible to provide appropriate scientific evidence for enhanced global warming before consequences escalate to potentially dire levels

▪ According to the precautionary principle, the onus falls on those contributing to the enhanced greenhouse effect to either reduce their input or demonstrate their actions do not cause harm - this makes it the responsibility of governments, industries, communities and even the individual

▪ The precautionary principle is the reverse of previous historical practices whereby the burden of proof was on the individual advocating action

5.2.5  Evaluate the precautionary principle as a justification for strong action in response to the threats posed by the enhanced greenhouse effect

Arguments for Action

▪ Risks of inaction are potentially severe, including increased frequency of severe weather conditions (e.g. droughts, floods) and rising sea levels

▪ Higher temperatures will increase the spread of vector-borne diseases ▪ Loss of habitat will result in the extinction of some species, resulting in a loss of

biodiversity▪ Changes in global temperature may affect food production , resulting in famine in

certain regions▪ The effects of increased temperatures (e.g. rising sea levels) could destroy certain

industries which countries rely on, leading to poverty▪ All of these consequences could place a far greater economic burden on

countries than if action were taken now

▪ These factors would increase competition for available resources, potentially leading to increased international tensions

Arguments for Inaction

▪ Cutting greenhouse emissions may delay economic growth in developing countries, increasing poverty in these regions

▪ Very difficult to police - what level of action would be considered sufficient on a global scale in the current absence of scientific consensus?

▪ Boycotting trade with non-compliant countries could negatively effect economies and create international tensions

▪ No guarantee that human intervention will be sufficient to alter global climate patterns ▪ Money and industrial practices that may be used to develop future technologies may be

lost due to restrictions imposed by carbon reduction schemes▪ Carbon reduction schemes will likely result in significant job losses from key industries,

retraining workers will require significant time and money

5.2.6  Outline the consequences of a global temperature rise on arctic ecosystems

Increases in global temperature pose a credible threat to arctic ecosystems, including :

▪ Changes in arctic conditions (reduced permafrost, diminished sea ice cover, loss of tundra to coniferous forests)

▪ Rising sea levels ▪ Expansion of temperate species increasing competition with native species (e.g. red fox

vs arctic fox)▪ Decomposition of detritus previously trapped in ice will significantly increase

greenhouse gas levels (potentially exacerbating temperature changes)▪ I ncreased spread of pest species and pathogens (threatening local wildlife)▪ B ehavioural changes in native species ( e.g. hibernation patterns of polar bears,

migration of birds and fish, seasonal blooms of oceanic algae)▪ Loss of habitat (e.g. early spring rains may wash away seal dens)Extinction and resultant loss of biodiversity as food chains are disrupted5.3.1 Outline how population size is affected by natality, immigration, mortality and emigration

The change in population size over a given period of time can be summarised by the following equation:  Population Size  =  ( N + I )  -  ( M + E )

Natality:  Increases to population size through reproduction (i.e. births)

Immigration:  Increases to population size from external populations 

Mortality:  Decreases to population size as a result of death (e.g. predation, senescence)

Emigration:  Decreases to population size as a result of loss to external populations

5.3.2 Draw and label a graph showing the sigmoid (S-shaped) population growth curve

Population Growth Curve

5.3.3 Explain reasons for the exponential growth phase, the plateau phase and the transitional phase between these two phases

Initially, population growth may be slow, as there is a shortage of reproducing individuals which may be widely dispersed

As numbers increase and reproduction gets underway, three stages of population growth are seen:

Exponential Growth Phase

▪ There is a rapid increase in population size / growth as the natality rate exceeds the

mortality rate▪ This is because there is abundant resources (e.g. food, shelter and water) and limited

environmental resistance (disease and predation uncommon)

Transitional Phase

▪ As the population continues to grow, eventually competition increases as availability of resources are reduced

▪ Natality starts to fall and mortality starts to rise , leading to a slower rate of population increase

Plateau Phase

▪ Eventually the increasing mortality rate equals the natality rate and population size becomes constant

▪ The population has reached the carrying capacity (K) of the environment▪ Limited resources, predation and disease all contribute to keeping the population size

balanced▪ While the population size at this point may not be static, it will oscillate around the

carrying capacity to remain relatively even (no net growth)

5.3.4 List three factors that sets limits to population increase

▪ Every species has limits to the environmental conditions it can endure and must remain within appropriate levels for population growth to occur

▪ Some of these factors are density-dependent, while others are unrelated to the density of the population

Factors affecting population growth:

5.4.1 Define evolution

Evolution is the cumulative change in the heritable characteristic s of a population

5.4.2 Outline the evidence for evolution provided by the fossil record, selective breeding

of domesticated animals and homologous structures

Something provides evidence for evolution when it demonstrates a change in characteristics from an ancestral form

The Fossil Record

A fossil is the preserved remains or traces of any organism from the remote past  

Fossil evidence may be either: 

▪ Direct (body fossils):   Bones, teeth, shells, leaves, etc. ▪ Indirect (trace fossils):   Footprints, tooth marks, tracks, burrows, etc.

Types of Fossils

The totality of fossils (both discovered and undiscovered) is known as the fossil record

▪ The fossil record reveals that, over time, changes have occurred in features of organisms living on the planet (evolution)

▪ Moreover, different kinds of organisms do not occur randomly but are found in rocks of particular ages in a consistent order (law of fossil succession)

▪ This suggests that changes to an ancestral species was likely responsible for the appearance of subsequent species (speciation via evolution)

▪ Furthermore, the occurrence of transitional fossils demonstrate the intermediary forms that occurred over the evolutionary pathway taken within a single genus

Law of Fossil Succession

While fossils may provide clues regarding evolutionary processes and ancestral relationships, it is important to realise that the fossil record is incomplete

▪ Fossilization requires a unusual combination of specific circumstances to occur, meaning there are many gaps in the fossil record

▪ Only the hard parts of an organism are preserved and often only fragments of fossilized remains are discovered

Fossilization

Selective Breeding

Selective breeding of domesticated animals is an example of artificial selection, which occurs when man directly intervenes in the breeding of animals to produce desired traits in offspring

As a result of many generations of selective breeding, domesticated breeds can show significant variation compared to the wild counterparts, demonstrating evolutionary changes in a much shorter time frame than might have occurred naturally

Examples of selective breeding include:

▪ Breeding horses for speed (race horses) versus strength and endurance (draft horses)▪ Breeding dogs for herding (sheepdogs), hunting (beagles) or racing (greyhounds)▪ Breeding cattle for increased meat production or milk▪ Breeding zebras in an attempt to retrieve the colouration gene from the extinct Quagga

Homologous Structures

▪ Comparative anatomy of groups of animals or plants shows certain structural features are basically similar, implying a common ancestry

▪ Homologous structures are those that are similar in shape in different types of organisms despite being used in different ways

▪ An example is the pentadactyl limb structure in vertebrates, whereby many animals show a common bone composition, despite the limb being used for different forms of locomotion (e.g. whale fin for swimming, bat wing for flying, human hand for manipulating tools, horse hoof for galloping, etc.)

▪ This illustrates adaptive radiation (divergent evolution) as a similar basic plan has been adapted to suit various environmental niches

▪ The more similar the homologous structures between two species are, the more closely related they are likely to be

Homologous Structures (Pentadactyl Limb)

5.4.3  State that populations tend to produce more offspring than the environment can

support

▪ The Malthusian dilemma states that populations tend to multiply geometrically, while food sources multiply arithmetically

▪ Hence populations tend to produce more offspring than the environment can support

5.4.4  Explain that the consequence of the potential overproduction of offspring is a struggle for survival

▪ When there is an abundance of resources, a population can achieve a J-curve maximum growth rate (biotic potential)

▪ However, with more offspring there will be less resources available to other members of the population (environmental resistance)

▪ This will lead to competition for available resources and a struggle for survival▪ Intraspecific competition occurs when members of the same species compete for the

same resources in an ecosystem (e.g. light, food, water)▪ It is density dependent, as the available resources must be shared among members of

the species▪ Competition that occurs between different species for resources is interspecific▪ The result of this competition will be an increase in the mortality rate, leading to an S-

curve growth rate as the population approaches the carrying capacity (K)

5.4.5  State that members of a species show variation

Members of a species show variation, which can manifest itself in one of two forms:

▪ Discontinuous variation:   A type of variation usually controlled by a single gene, which leads to distinct classes (e.g. ABO blood group in humans)

▪ Continuous variation :  A type of variation controlled by many genes, which leads to a

range of characteristics (e.g. skin pigmentation in humans) 

There are three primary sources of variation within a given population

▪ Gene mutations   (a permanent change to the genetic composition of an individual)▪ Gene flow   (the movement of genes from one population to another via immigration and

emigration)▪ Sexual reproduction (the combination of genetic materials from two parental sources) 

5.4.6  Explain how reproduction promotes variation within a species

There are three primary ways by which sexual reproduction promotes variation within a species:

Independent Assortment

▪ During metaphase I, when homologous chromosomes line up at the equator, the paired chromosomes can randomly arrange themselves in one of two orientations (paternal left / maternal right  OR  maternal left / paternal right)

▪ When the chromosomes separate in anaphase I, the final gametes will differ depending on whether they got the maternal or paternal chromosome

▪ Independent assortment of chromosomes creates 2 n different gamete combinations (n = haploid number of chromosomes)

Crossing Over

▪ During prophase I, when homologous chromosomes pair up as bivalents, genetic information can be exchanged between non-sister chromatids

▪ The further apart two genes are on a chromosome, the more likely they are to recombine

▪ Crossing over greatly increases the number of potential gamete variations by creating new genetic combinations

Random Fertilisation

▪ Fertilisation results from the fusion of gametes from a paternal and maternal source, resulting in offspring that have a combination of paternal and maternal traits 

▪ Because fertilisation is random, offspring will receive different combinations of traits every time, resulting in near infinite genetic variability

5.4.7  Explain how natural selection leads to evolution

The theory of natural selection was postulated by Charles Darwin (and also independently by Alfred Wallace) who described it as 'survival of the fittest'

▪ There is genetic variation within a population (which can be inherited)▪ There is competition for survival (populations tend to produce more offspring than the

environment can support)▪ Environmental selective pressures lead to differential reproduction▪ Organisms with beneficial adaptations will be more suited to their environment and

more likely to survive to reproduce and pass on their genes▪ Over generations there will be a change in allele frequency within a population

(evolution)

5.4.8  Explain two examples of evolution in response to environmental change; one must be antibiotic resistance in bacteria

Example 1:  Staphylococcus aureus (associated with a variety of conditions, including skin and lung infections)

Variation:  Antibiotic resistance (some strains have a drug-resistant gene ; other strains do not)

Environmental change:  Exposure to antibiotic (methicillin)

Response:  Methicillin-susceptible S. aureus (MSSA) die, whereas methicillin-resistant S. aureus (MRSA) survive and can pass on their genes

Evolution:  Over time, the frequency of antibiotic resistance in the population increases (drug-resistant gene can also be transferred by conjugation)

Example 2:  Peppered Moth (Biston betularia)

Variation:  Colouration (some moth have a light colour, while others are a darker melanic colour)

Environmental change:  Pollution from industrial activities caused trees to blacken with soot during the Industrial Revolution

Response:  Light coloured moths died from predation, whereas melanic moths were camouflaged and survived to pass on their genes

Evolution:  Over time, the frequency of the melanic form increased (with improved industrial practices, the lighter variant has become more common) 

5.5.1  Outline the binomial system of nomenclature

The binomial system of nomenclature was devised by Carolus Linnaeus as a way of classifying organisms that was globally recognised and could demonstrate evolutionary relationships between organisms (and thus allow for the prediction of features closely related organisms may share)

According to the binomial system of nomenclature, every organism is designated a scientific name with two parts:

▪ Genus is written first and is capitalised (e.g. Homo)▪ Species follows and is written in lower case (e.g. Homo sapiens)▪ Some species may also have a sub-species designation (e.g. Homo sapiens sapiens)▪ Conventions:  When typing, the name should be in italics; whereas when hand writing,

it should be underlined 

5.5.2  List the seven levels in the hierarchy of taxa - kingdom, phylum, class, order, family, genus and species - using an example from two different kingdoms for each level

When classifying living things, organisms are grouped according to a series of hierarchical taxa - the more similar their characteristics, the closer the grouping

Classification of Animals and Plants

5.5.3  Distinguish between the following phyla of plants, using simple external recognition features: bryophyta, filicinophyta, coniferophyta and angiospermophyta

5.5.4  Distinguish between the following phyla of animals, using simple external recognition features: porifera, cnidaria, platyhemlnthes, annelida, mollusca and arthropoda

5.5.5  Apply and design a key for up to eight organisms

A dichotomous key is a method of identification whereby a group of organisms are sequentially divided into two categories until all are identified

Example of a Dichotomous Key:

1.  Organism is a plant ...................................................................................... Go to Q2

     Organism is not a plant (animal) ................................................................ Go to Q5

2.  Has no 'true' leaves or roots ....................................................................... Bryophyta

     Has leaves and roots ................................................................................... Go to Q3

3.  Has no seeds (sporangia) .......................................................................... Filicinophyta

     Has seeds ..................................................................................................... Go to Q4 

4.  Has no flowers ............................................................................................. Coniferophyta

     Has flowers ................................................................................................... Angiospermophyta

5.  Asymmetrical body plan ............................................................................. Porifera

     Symmetrical body plan ............................................................................... Go to Q6

6.  Has radial symmetry ................................................................................... Cnidaria

     Has bilateral symmetry ............................................................................... Go to Q7

7.  Has no anus ................................................................................................. Platyhelminthes

     Has an anus ................................................................................................. Go to Q8

8.  Has a segmented body .............................................................................. Go to Q9

     Has no visible body segmentation ........................................................... Mollusca

9.  Have an exoskeleton ................................................................................. Arthropoda

     Have no exoskeleton ................................................................................. Annelida

Dichotomous Key as a Flowchart