It is now Saturday morning and snow is falling as I sit here planning our next week. The forecast worries me as there is a possibility of delay or cancellation Monday. We are already a few days behind the preferred point, and need each day. Monday's double lab is important. In preparation, please review the ppt slides on the docs page and read the following information. I will expect you to come with questions. I will briefly review this segment and begin our lecture with slide 44. IF there is no class Monday, I will have notes on-line for you. We must keep moving.

Slides 37-40 recall the Isle Royale reading and graphing activity we did in class. Please review this – including density dep and indep factors affecting populations. How wold you categorize UV radiation? H1N1?

Slides 41-43 introduce the idea of reproductive strategy. In order for a species to survive it must reproduce and offspring must survive. The qualities of the perfect mother are listed for you; as you look at them realize that NO female of any species meets all of these criteria. It takes far too much energy to do so. Species tend to fit into two categories.

1st category - Mothers that reproduce often, have MANY (hundreds, thousands) at once, but the young are on their own (no nurturing). All energy is used to PRODUCE young. These are called r-selected species. They typically have short life-spans. Examples include mosquitoes, frogs and turtles. These species typically experience high rates of mortality among the young, but if offspring survive to adulthood, their chances of long term survival are good. In this case, the hope is that enough will survive to carry on the species.

2nd category- The alternative is to have fewer offspring, but to nurture them to maturity to increase the likelihood of survival of as many of the young as possible. The mother’s energy must be managed differently – all cannot be expended on reproduction, as energy is needed to provide ongoing food and care of the young. These are called K-selected species and examples include kangaroos, elephants, and humans. These species typically experience moderate to low infant mortality, low mortality among adolescents and adults until old age. The chances of reaching old age (for that particular species) are high.

Of course, in nature, there are organisms that fall in between these categories—they have an intermediate number of offspring, or they nurture for part of the offspring’s life, etc. Examples include some species of birds that have multiple eggs, nurture them to adolescence and then they are on their own.

The survivorship curve types correlate to these r- and K-selected reproductive strategies.

Graph interpretaion: Note that the survivorship curve makes it look like more humans survive overall than mosquitoes. The Y axis is simply comparing the fate of 1000 offspring of different species. We use this 1000 as a comparison. In a give year there are of course many more mosquitoes “born” than humans.

What reproductive strategy correlates to the type I curve? What reproductive strategy correlates to the type III curve? What do all survivorship curves have in common? What strategy do mice employ? Rattlesnakes?

Why can’t a mother be “perfect”? (--Though we do try….)

Please spread the word to your classmates to read the notes above.