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Do Now 03/06. What growth curve do humans exhibit currently and why? Draw the curve, label it, and explain when it is best exhibited by populations. 2-3 sentences. Sort the lot.
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Do Now 03/06 • What growth curve do humans exhibit currently and why? Draw the curve, label it, and explain when it is best exhibited by populations. 2-3 sentences.
Sort the lot • In front of you at your tables, you have a group of characteristics that you need to categorize under either K- selected or R-selected. • R-selected: unstable environment, density independent • K-selected: stable environment, density dependent
Today we will… • 4.3: I can explain the differences between R and K reproductive strategies and apply the concept to the human population and other species • 4.4 I can explain what the three different types of survivorship curves are and apply the concept to humans and other species
Reproductive strategy types • There are two types of reproductive patterns that allow organisms to pass down genes to their offspring. • 1. Asexual: offspring are genetic copies of their parents. Many Plants and animals, like corals, reproduce this way • 2. Sexual reproduction: requires the mixing of genetic material from gametes and produces and offspring with a combination of parents genetic material.There are 3 disadvantages to sexual reproduction: • 1) males do not give birth • 2) there is an increased chance of genetic errors and defects in the splitting and recombining of genetic material, and • 3) courtship and mating rituals consume time and energy, transmit disease, and can inflict injury on males as they compete for mates. • Why do species sexually reproduce?--> it allows for contributed biodiversity , thus giving the population a greater chance of reproducing when conditions change.
R and K life patterns • These life patterns are exhibited by specific organisms. They can either be K-selected or R-selected. These tell us on how species reproduce and raise their young.
R-selected species • Species with a high rate of population increase are classified as R-selected. • These species usually havea lot of very small offspring, and give them no parental care. • They overcome a massive loss of offspring by producing many at once. • Things like bacteria, algae, rodents, cockroaches and other insects follow this pattern. • They produce as many offspring as possible in order to increase their chances of having a few reproduce later in their lifetime. • These species are opportunists invading new environments when given the chance, but go through boom and bust cycles in their population size.
K-selected • K-selected species are competitor species. • They reproduce later in life and have a small number of offspring with fairly long life-spans. • These species usually develop inside their mothers, are born fairly large, develop slowly, and are cared for and protected by the parents: there is significant energy investment in offspring care. • This results in a few large and strong individualsthat can compete for resources. • These species are known a k-selected because they tend to do well in competitive situations, as is when a population reaches its carrying capacity, or K. • These populations typically follow the logistic growth curve. Animals like elephants, large birds of prey, and some plants follow this pattern. • Animals that have very long generation times are usually prone to extinction.
Quick Check • What reproductive pattern do humans follow? Why? • What is the difference between K vs. R selected species? • What reproductive pattern is best suited for exponential growth? Why? • What reproductive pattern is best suited for logistic growth? Why?
Active Practice (P.5) • Explain why most species with a high capacity for population growth tend to have a small size, such as bacteria and flies, while those with a low capacity for population growth tend to be large (like humans, elephants, and whales)?3-4 sentences. • 2. Why are pest species likely to be extreme r-selected species? Why are many endangered species likely to be extreme k-selected? Explain your answer in 3-4 sentences. • 3. What are some drawbacks in being a competitor species versus an opportunist species? If you were stranded on a deserted island, what reproductive strategy would work best and why? • 4. Make a t-chart for the differences between R and K-selected strategies.
Survivorship curves • There 3 types: I, II and III • Survivorship curves • Individuals of species with different reproductive patterns tend to have different life expectancies. Survivorship curves show us the percentages of the members of a population surviving at different ages. There are three types: early loss, late loss, and constant loss.
Type I: Late Loss • Late loss (I): most individuals live to adulthood, with most mortality occurring in old age. Humans follow this pattern, as well elephants and monkeys. This would be represented by the convex curve.
Type II • Constant loss (II): an organisms chance of dying is independent of age. Present with many birds. This would be represented by the straight line. Can follow a r-selected pattern
Type iii • Early loss (III): you have a large number of offspring at once, then a large proportion die off in very little time. • This can relate to a lot of species that follow r-selected reproductive strategies. Identified by a concave line on the percentage surviving vs. age graph. Very few live to adulthood, with many dying at an early age.
Quick check • What survivorship curve best represents a situation in which many offpsring are made at once and die very early in age? • What curve do you think trees follow? Why?
