POPULATIONS Population-all of the individuals of a species that live together in one place at one time. Demography-the statistical study of populations. It is used to predict how the size of a population will change.
PREDICTING POPULATION GROWTH, Nearly all populations will tend to grow exponentially as long as there are resources available.
Populations Growth Three factors can affect population size: –number of births –the number of deaths –the number of individuals that enter or leave the population. * Simply put, a population will increase or decrease in size depending on how many individuals are added to it or removed from it Rate of Growth r = birth rate – death rate +/- migration
Immigration & Emigration Immigration –the movement of individuals into an area, is another factor that can cause a population to grow. Emigration –the movement of individuals out of an area, can cause a population to decrease in size.
PREDICTING POPULATION GROWTH Exponential growth curve: population growth plotted against time. As a population gets larger, it also grows at a faster rate. This is the maximum population growth under ideal circumstances. Includes plenty of room for each member, unlimited resources (food, water) and no hindrances (predators). FACT: No population exhibits this type of growth for long.
Two modes of population growth. The Exponential curve (also known as a J- curve) occurs when there is no limit to population size. The Logistic curve (also known as an S-curve) shows the effect of a limiting factor (in this case the carrying capacity of the environment).
Populations “Candidates should be able to draw a generalised graph of population growth when provided with appropriate data”
Abiotic Factors Light Wind / water currents Oxygen availability Edaphic (Soil) factors Water availability Temperature
Light Plants need light. Some are adapted to live with low levels, others need full sun – part of their niche Remember the statistics we did in transition? Ivy leaf area size… Amount of light also dictates some animal behaviours, e.g. reproduction
Temperature All organisms can live in a particular range of temps. It mainly affects action of enzymes Many animals evolve behaviours and features which allow them to survive in extreme temps. Those without adaptations die.
Wind/Water currents Wind increases water and heat loss adding to environmental stress Whole woodland ecosystems can be destroyed by storms and gales In water currents, organisms need to be able to hold on or swim against them Sudden floods can be devestating to populations.
Water availability Water is vital for organisms Availability in terrestrial environments depends on rainfall, evaporation and edaphic (soil) factors Again adaptations exist to survive desert areas…. …Name some!
Oxygen availability Cold running water holds more O2 than still warm water and therefore can support more life. Soil needs oxygen in it too. Why? Waterlogged soil has no air spaces so if this occurs many plants die Mangroves and others have aerial roots to stop this happening.
Edaphic Factors: soil structure/mineral content Soil structure can affect populations associated with it Sand is loose and free draining, few plants are adapted well to this (e.g. marram grass) Sandy soils leach easily. Clay soils don’t drain well
Loam soils has a wide range of particles so drains nicely, but less prone to leaching and warms up and is easily worked unlike clays.
Predation Predator-prey relationships oscillate in a repeating pattern. Shown in a mathmatical model and in real popns. More complex though, hares oscillate whether lynx or not. Variations in food and insects the reason. You must study all aspects of an ecosystem to know this Classical example of predator/prey relationships. Snowshoe hare vs. lynx numbers in Canada based on number of skins collected by hunters!
Mates “Reproduction is a powerful driving force” Availability of mates has a big effect on the abundance of any type of animal in an area. Territory – an area held and defended by an animal (or group) Usually to make sure a breeding group has enough resources to bring up offspring Territory
Parasitism and Disease …both can be devastating Diseased animals don’t reproduce well, they cant hunt effectively prey animals are more likely to be caught Parasites feed off their hosts this weakens them The higher the population, the more it will be affected by parasites and disease – a density dependant factor
Population ecology When studying an ecosystem, it is hard to distinguish between biotic and abiotic factor effects It is also rare that one factor works alone It is important you study all factors in the environment:
Density-dependent and non-density dependent factors Factors affecting the number of organisms occupying a niche may be density dependent or density independent Density independent factors have the same effect despite the size of the population. – They tend to influence the distribution of individuals and hence the population
The effect of density dependent factors will depend on the numbers of individuals in a population. – Density dependent factors therefore tend to affect the abundance of a species What’s Carrying Capacity? – Its dependant on on availability of resources – Which therefore act as a DD factor – Population may fluctuate around the k value
Competition …often occurs between individuals for density-dependent factors. It occurs when 2 organisms are competing for a limited resource It may be for biotic factors such as mates Or for abiotic factors such as sunlight or minerals
Inter- and intra-specific competition Intra-specific competition occurs within a species Inter-specific competition occurs between species
Control of Populations Chemical Control – To your phones! – Investigate…. Biological control
Chemical ControlBiological Control Efficiency Environmental Damage Ease of Use Effects on Human Life
Biological Control Definition “The use of living organisms to suppress the population of a specific pest organism, making it less abundant or less damaging than it would otherwise be” (Eilenberg et al., 2001)
Survive longer in the field but have low virulence Biological alternative to chemical insecticides Pathogens
Bacteria 1921: reported in Japan. 1940s: Commercial prep. Available in France 39% of biopesticides Lep, Dip and Colep strains Crystals containing poison Out of all, Bacillus thurigiensis is the most used
Viruses Out of 6 groups only 3 are safe: -Nuclear Polyhedrosis Virus (NPV) -Granulosis visus (GV) -Citoplasmic Polyhedrosis Virus (CPV) Family Specific Need to be ingested
Organic Breakdown Organic breakdown is important in an ecosystem It breaks down dead organic matter releasing locked up nutrients Micro-organisms play a vital role in this process Dead organisms go through a number of decomposition stages:
Five Stages of Decomposition Fueled by Insect Activity. Fresh Bloat Decay Post-decay Dry (skeletal) – This is extra to the syllabus but interesting stuff!
Fresh Begins at death Flies begin to arrive Temperature falls to that of the ambient temperature. Autolysis, the degradation of complex protein and carbohydrate molecules, occurs.
Bloat Swells due to gases produced by bacteria Temperature rise of the corpse Flies still present
Decay Gases subside, decomposition fluids seep from body. Bacteria and maggots break through the skin. Large maggot masses and extreme amounts of fluid. Unpleasant odor Larvae beginning to pupate. Corpse reduced to about 20% of it’s original mass.
Post-Decay Carcass reduced to hair, skin, and bones. Fly population reduced and replaced by other arthropods. Hide beetles are dominant in dry environments. Mite and predatory beetle populations increase.
Dry (Skeletal) Does not always occur especially if corpse is in a wet region. Maggots will stay longer and hide beetles will not appear. In wet environments the hide beetles are replaced with nabid and reduviid insects. The corpse is reduced to at least ten percent of the original mass. In the last stage (Skeletal Stage), only bone and hair remain.
Nutrient cycling You need to be able to draw out a fully labelled diagram of the Carbon and Nitrogen cycles
Carbon Cycle in Nature Complex cycles exist which ensure chemical constituents of life are constanly recycled in the environment. These cycles include both a biotic phase and an abiotic phase Carbon is fundamental to the formation of organic molecules (see AS course) There is a massive pool of carbon in the CO 2 in the atmosphere and in the ocean, lakes and rivers.
Carbon Cycle What is X? What is Z? Respiration Decomposers
Dynamic equilibrium Carbon moves back and forth between the atmosphere and living things The transfers cancel each other out, so the net effect is no change e.g. Photosynthesis removes CO 2 from the atmosphere and converts it into plant leaves, stems and roots Respiration returns CO 2 to the atmosphere by oxidising sugars Photosynthesis and respiration are in balance
Gaia Hypothesis The atmospheric composition and temperature of the earth are actively controlled by life on the planet i.e. the whole planet can be thought of as a living organism. The hypothesis proposes that negative feedback will correct any deviation Since the Industrial revolution, humans have significantly increased the amount of CO 2 in the atmosphere The Gaia hypothesis suggests that natural processes would work to reverse this e.g. Photosynthesis would speed up to absorb this extra CO 2 Resulting global warming would cause storms and flooding that destroy industry? Suggests that the Earth will respond, via abiotic changes, to correct human disturbances Suggests that humans should take great care not to upset the complex interactions between the biotic and abiotic environment James Lovelock
Impact on the Carbon cycle respiration carbon compounds in tertiary consumers feeding carbon compounds in secondary consumers feeding carbon compounds in plants photosynthesis Death carbon compounds in dead organisms carbon in fossil fuels carbon calcium carbonates sedimentation Decomposition by fungi burning weathering precipitation carbon compounds in primary consumers carbon dioxide in air or dissolved in water
Nitrogen Cycle What biological compounds contain nitrogen? – Proteins and the amino acids they are made of – Nucleic acids You get your N from your diet Plants can only get it from ion uptake from the soil, which ions? – Ammonium and nitrate
Nitrogen Cycling Processes Nitrogen Fixation – bacteria convert nitrogen gas (N 2 ) to ammonia (NH 3 ). Putrefaction – dead nitrogen fixers release N-containing compounds. Nitrification – type of chemosynthesis where NH 3 or NH 4 + is converted to nitrite (NO 2 -) ; other bacteria convert NO 2 - to nitrate (NO 3 -). Ploughing and drainage are essential for aerating the soil to keep the conditions right for these bacteria! Denitrification – bacteria convert NO 2 - and NO 3 - to N 2.
Nitrogen Fixation The nodules on the roots of this bean plant contain bacteria called Rhizobium that help convert nitrogen in the soil to a form the plant can utilize. Lets look at some under the microscope…