Ecology Biology 30 Ecology Study of Ecosystems Abiotic & Biotic factors interacting Biotic Factors include populations & communities Population •Same species •Same place •Same time Community •Groups of pops interacting Same species: Same place: Same time! Can you explain the difference between a population and a community? The definition for a population? The definition for a community? Biotic and Abiotic Factors? Abiotic factors are the non-living components of an ecosystem Biotic factors are the living components of an ecosystem Can you tell me… The difference between abiotic and biotic factors in an ecosystem? An example of an abiotic factor? An example of a biotic factor? Ecosystem Community or Population? Community _________________ Why is the picture in the previous slide an example of a community and not an example of a population? Populations Variables we will consider: Geographic Range Habitat Ecological Niche Population Distribution Population Size Population Density Population Growth Rate and Patterns Geographic Range area where animal has been seen Fire Ant Range Geographic range can change over time due to abiotic factors. Range Changes in Moose Populations How has the geographic range of moose changed since the 1870’s?? Habitat area where the population lives where environmental conditions are best for survival How does an organism’s geographic range differ from its habitat? Ecological Niche Role of the species in the community Includes ALL biotic and abiotic factors a species needs to survive Each group has a different role to minimize competition Populations co-exist only if each group occupies a different niche Explain the meaning of the term ecological niche. Population Distribution Uniform Clumped Population Distribution Determined largely by habitat preference Divided into three patterns: 1. Clumped - individuals grouped in patches due to certain environmental factors (e.x. trees clump on south slopes of river valleys b/c less direct sunlight and sturdier soils) 2. Random - not very common - biotic and abiotic factors have little effect 3. Uniform competition among individuals for resources results in regular spacing What is the difference between clumped, random and uniform population distribution? What factors are responsible for creating clumped, random and uniform population distributions? Population Size Number of organisms of same type in same place, at same time There are 2000 students at Centre High during the 2004/5 school year. Can be determined by exact count or estimation!! Population Density Describes number of organisms in a defined area eg. Snow geese at Beaver Hills = # of geese per hectare Density (D) calculated by dividing total number (N) by amount of space occupied (S) by the population What is the difference between population size and population density? Density Example If 200 lemmings are living in a 25 hectare (ha) area of tundra, what is the population density of this area? Use the formula D = N/S Growth Rate After finding the population density, we can find the rate of change over time Change in number Rate of growth Change in time Density Change example In 1993, the mouse population in my backyard was 50 mice/acre. After three years, various control measures had been in place, and the population dropped to 10 mice/acre. Calculate the rate of density change. When arriving at their summer cabin, the Smiths discovered 10,000 cockroaches roaming throughout their 1000 m2 cabin. After 1 week, the exterminators were able to control the situation and reduced the cockroach population to 10 per 1000 m2. Calculate the rate of density change. Population Growth Determined by four factors: Natality Mortality Immigration Emmigration Population Growth Also known as per capita growth rate Calculation Using this table, calculate CGR for Sandhill cranes: Puffins are small marine birds found off the coast of Atlantic Canada. Calculate the population growth rate of a puffin colony based on the following population in 1999. Original population = 200 000 Natality = 15 000 Mortality = 10 000 Immigration = 175 000 Emigration = 160 000 Density Problem Calculate the population density of shrews per m2, if an average of 7.8 shrews are found in an area 14 m wide by 20 m. CGR Calculation Calculate the per capita growth rate of a mouse population if the original population size is 34 and over a period of a week, 5 die, 8 are born, 12 immigrate into and 7 emigrate out of the area. Dynamic Equilibrium Present in mature ecosystems Characterized by long term balance Pops remain relatively stable over time Great biodiversity = stability Can be compared with homeostasis Define dynamic equilibrium. 2 population types: 1. Open populations: immigration & emigration occurs 2. Closed populations: Density changes are result of natality and mortality only No immigration or emigration eg. Game preserves What is the difference between open and closed populations? Growth Curve Graph showing changes in a population over time. X = time (independent or manipulated variable) Y = density or # of organisms (dependent or responding variable) Exponential Pop Growth Growth Curve for Closed System 4 phases: 1. Lag phase…slow…not enough reproducing organisms 2. Growth phase….exponential increase 3. Stationary phase….natality= mortality 4. Death phase…decline Not always present Bacterial Growth Curve Closed population 4 distinct phases Draw a growth curve for a closed population. Label and define the four stages of this curve. Growth Curve for Open Systems When a limiting factor is introduced to a population, curve results in an “S” shape As organisms respond to increased nutrients, natality increases. Typical of an organism placed in a new environment Equilibrium is established again and curve levels off New carrying capacity (max. # of individuals environment can support) Define carrying capacity. When does a population growth curve of an open system show an “S shape”? Population Growth Curves Click on the link above Read the instructions and hit the “run applet” button Set the carrying capacity to 1000 Set the birth rate to 1.5 Hit RUN View the graph and draw this in your notes Have you simulated an open or a closed population? Change the parameters and try it again! Population Curves Human Population Growth Population Curves Population Curves How could you describe the population growth of humans in the past 500 years? Hint: one word that begins with an ‘e’ Population Explosion & Crashes Describe the bottleneck effect. Boom and Bust Cycles What trends do you see in the population curve for Soay Sheep that give its characteristic shape of “boom and bust”? Survivorship Curves Population Curves Population Curves Population Histograms Wide base…fast growth Narrow base….decline What information is given in a population histogram? What shape would a histogram look like if it were representing an declining population? A stabilized population? A young population? More Histograms What are these graphs showing? 1. Which country demonstrates a very high reproductive rate? 2. Which country represents a stabilized population? Show Age Structure of Pop Histograms What do each of the histograms on slides 63 to 64 tell you? What trends do you see in the population curves on slides 63 to 64? Biotic Potential Max. # of offspring produced in ideal conditions Regulated by four factors: offspring - max #/birth survival capacity – chance that offspring will reach reproductive age procreation - # times/year organism reproduces maturity - age when reproduction begins Environmental Resistance All factors that limit pop. growth Can be biotic or abiotic Examples include……. Food, water, space, disease, predation, natural disasters, availability of mates, etc Environmental Resistance In a fresh water habitat Define biotic potential and environmental resistance. Give an example for environmental resistance. Limiting Factors Affect population size! flood, fire, extreme cold, disease, starvation, predation Law of the minimum various substances are required for growth. the one with the lowest concentration will limit growth ( known as limiting factor) Limiting Factors can be: Density Independent: affecting pop regardless of # of individuals flood, fire, extreme cold, other abiotic factors Density Dependent: affecting pop & dependent on pop size disease, starvation, predation State the law of the minimum. Define limiting factors. What are some examples of limiting factors? Name the Density Dependent Factor! Pops can also be r or K Selected K - selected r - selected High Reproductive Rate Low Reproductive Rate Almost at Carrying Capacity K- selected Populations r- selected Populations Differentiate between r and K-strategies. Give 2 examples of the types of organisms that use each of these strategies.