Ecology Population Ecology
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DESCRIPTIONEcology Population Ecology. Populations. A population is a group of individuals of the same species living in an area. 3. Distribution Patterns. Populations disperse in a variety of ways that are influenced by environmental and social factors. - PowerPoint PPT Presentation
This is the second portion of the Ecology unit. 12Populations3.A population is a group of individuals of the same species living in an area
These iguanas live in trees over a River in the North East corner of Costa Rica. Like many lizards, iguanas are cold-blooded, which means they don't generate their own heat. However, these animals have adapted to live in a wide range of environments. While usually found in rainforest or near water, species of iguanas can be found in the desert and in other land environments where they get their water from their food sources.
Population ecology focuses on factors affecting population size over time.Density is the number of individuals per unit area or volumeDispersion is the pattern of spacing among individuals within the boundaries of the population2Distribution PatternsUniform distribution results from intense competition or antagonism between individuals.
Random distribution occurs when there is no competition, antagonism, or tendency to aggregate.
Clumping is the most common distribution because environmental conditions are seldom uniform.
Populations disperse in a variety of ways that are influenced by environmental and social factorsUniform and random distributions are relatively rare and occur only where environmental conditions are fairly uniform. A uniform distribution results from intense competition or antagonism between individuals.
Random distribution occurs when there is no competition, antagonism, or tendency to aggregate. The conditions are uniform. It is rare for all these conditions in the environment to be met.
Clumping is the most common distribution because environmental conditions are seldom uniform, reproductive patterns favor clumping, and animal behavior patterns often lead to congregation. The optimum density for population growth and survival is often an intermediate one; undercrowding can be as harmful as overcrowding.3
Fig. 52.1, Campbell & Reece, 6th ed.Clumped distribution in species acts as a mechanism against predation as well as an efficient mechanism to trap or corner prey. It has been shown that larger packs of animals tend to have a greater number of successful kills.What causes these populations of different organisms to clump together?Ask students to give examples of specific clumping descriptions: herd of cattle, flock of sheep, bale of turtles, etc. 4Population DispersalNatural range expansions show the influence of dispersal on distributionFor example, cattle egrets arrived in the Americas in the late 1800s and have expanded their distribution
They sure have! They are quite the pest in Texas.5Population DispersalIn rare cases, long-distance dispersal can lead to adaptive radiationFor example, Hawaiian silverswords are a diverse group descended from an ancestral North American tarweed
You just have to love guys with a good sense of humor! We used this photo found on the internet since it shows the scale of the Hawaiian silverswords. Another lesson in being careful about putting photos on the web, you just never know how theyll be used!
Adaptive radiation is the diversification of a group of organisms into forms filling different ecological niches. Ask students if they can give any examples. Some classics are: Darwins finches and the marsupials of Australia.
The Spread of the Africanized Honey Bee
When did they first arrive in the Americas?
How long did it take for them to expand their range into the US?
How can you explain their success in expanding their territory?
7Take this opportunity to let students practice interpreting graphics.
First arrived? Researchers brought the African bees to Brazil in the 1950s in an attempt to improve the productivity of Brazilian bees.
How long to reach US? 40 years! A large wild population quickly developed and spread through South America, Central America and Mexico. In the 1990's, the Africanized honey bee was identified in Texas and has since spread though the southwest US.
Why successful? Many correct answers including: African bees produce more offspring, defend their nests much more fiercely and in greater numbers and are more likely to abandon the nest when threatened by predators or adverse environmental conditions. 7Small Geographic Range
8Most species have a small geographic range8Species with a Large Geographic Range
9Moss Tetraphis- is a unique moss that has only 4 peristome (mouth or opening of an organ) teeth (most mosses have 8 to 64). It reproduces asexually when it is not fruiting. These adaptations have given this moss a large geographic range in which to inhabit. 9Interactions10
Interactions between organisms and their environments determine abundance and distribution of organisms. Ask students to postulate as to why the range of kangaroos follows this pattern. 1011Estimating Population SizeThe Mark-and-Recapture Technique
Count the total # of individuals, easy if the organisms are large and area is not too large.Divide the area into # of quadrants and count the number of individuals in several of quadrants and then estimate the entire area.Mark-and-recapture technique: A limited number of individual (e.g. 20) are captured at random and marked with a dye or tag and then are released back into the environment. At a later time a second group of animals is capture at random from the population and the percentage of marked individuals determined. Now if 10% of the animals in this second group is recaptured, then the original 20 represented 10% of the population and the population then is 200. 11Estimating Population SizeThe Mark-and-Recapture Technique12Emphasize that this method comes with a whopping assumption! Namely, that marked individuals have the same probability of being captured as unmarked individuals.12Lets Try an Example!13Twenty individuals are captured at random and marked with a dye or tag and then are released back into the environment.
Therefore s = # of animals marked = 20
At a later time a second group of animals is captured at random from the population
Emphasize that this is a simple proportionality and they should expect easy math! In other words, the numbers wont be too scary or abstract.13Lets Try an Example!141415Which method would you use?1. To determine the number of deer in the state of Virginia?
2. To determine the number of turkeys in a county?
3. To determine the number of dogs in your neighborhood?
4. To determine the number of ferrel cats in your neighborhood?Use the mark-recapture method to estimate the population since the area is vast.
2. Use the quadrant method from various areas around Virginia to estimate the population.
3. & 4. Simply count them since the area is small and the population numbers will be low.15Survivorship curvesWhat do these graphs indicate regarding species survival rate & strategy?
0251000100Human(type I)Hydra(type II)Oyster(type III)10150Percent of maximum life span10075Survival per thousandI.High death rate in post-reproductive yearsII.Constant mortality rate throughout life spanIII.Very high early mortality but the few survivors then live long (stay reproductive)16Type I curve is flat at the start, reflecting low death rates during early and middle life, then drops steeply as death rates increase among older age groups. Humans and many other large mammals that produce few offspring but provide them with good care often exhibit this kind of curve.
Type II curves are intermediate, with a constant death rate over the organisms life span. This kind of survivorship occurs in Beldings ground squirrels and some other rodents, various invertebrates, some lizards, and some annual plants.
Type III curve drops sharply at the start, reflecting very high death rates for the young, but then flattens out as death rates decline for those few individuals that have survived to a certain critical age. This type of curve is usually associated with organisms that produce very large numbers of offspring but provide little or no care, such as longlived plants, many fishes, and marine invertebrates. An oyster, for example, may release millions of eggs, but most offspring die as larvae from predation or other causes. Those few that survive long enough to attach to a suitable substrate and begin growing a hard shell will probably survive for a relatively long time.
1,000IIIIII100101100500Percentage of maximum life spanNumber of survivors (log scale)Ideal Survivorship Curves1717Ask some graphical analysis questions:
Which type of curve would best depict the survivorship curve of jellyfish? Type IIIWhich type of curve would best depict the survivorship curve of a lizard? Type II
Population Growth Curves18d = delta or changeN = population Sizet = timeB = birth rateD =death rate
18Population Growth Models
WOW! 1 bacterium (reproducing every 20 minutes), could produce enough bacteria to form a layer over the entire surface of the Earth 1 foot deep!19Exponential Growth Curves20d = delta or changeN = Population Sizet = timermax = maximum per capita growth rate of population
Population Size, NTime (hours)Growth Rate of E. coliOne of the most common examples of exponential growth deals with bacteria. Bacteria can multiply at an alarming rate when each bacteria splits into two new cells, thus doubling. For example, if we start with only one bacteria which can double every hour since it reproduces asexually, by the end of one day we will have over 16 million bacteria.