SGCEP BIOL 1020K Introduction to Biology II Spring 2012 Section Steve Thompson:

Transcription

1 SGCEP BIOL 1020K Introduction to Biology II Spring 2012 Section Steve Thompson: 1

2 OK, on to the easiest part of the course... Stuff you ve actually been learning all your life, perhaps even without realizing it. I m talking about green stuff... the theories and methods of ecology. 2

3 But first, those damn questions off the last exam that nearly everybody screwed up! 2. In the general consensus phylogenetic tree of life for the organisms in question #1 that I presented: A. The multiple endosymbiotic events that produced the chloroplast, correlate with phylogenetic placement B. They all evolved from some ancestral Bacterial or Archaeal organism more than 10 billion years ago C. All of these organisms sort into only three primary, basal clades of life: plants, animals, fungi D. Several different endosymbiotic events produced the mitochondria 7. The Apicomplexans are monophyletic in the SAR clade Alveolata; which statement is not true about them? A. Apicomplexans are all spore-forming animal parasites, with an apical complex involved in host interaction B. The other SAR clade Alveolata members are the Dinoflagellates and the Ciliates C. The malaria parasite Plasmodium is an example D. Apicomplexans are all autotrophic 3

4 13. Which of the following statements is not true regarding the conifers (Pinophyta)? A. They include pines, firs, spruces, cedars, junipers, cypresses, hemlocks, and yews B. They have various types of leaves ranging from scales to fronds to needles C. They produce both seeds and pollen separately in cones D. They all retain their leaves year-round as evergreens 26. A bauplan (body plan) in which any plane lengthwise through the body divides it into mirror images is: A. Dorsal ventral symmetry B. Bilateral symmetry C. Radial symmetry D. Asymmetry 4

5 33. Within the Insects, which clade (order) contains all the beetles (and is the largest clade of all the insects)? A. Hymenoptera B. Lepidoptera C. Coleoptera D. Hemiptera 34. The Echinodermata have spiny external surfaces; which of the following statements is not true about them? A. They all have radial symmetry at all points in their life cycle, i.e. both as a larva and as an adult B. Starfish, sea cucumbers, sand dollars, and sea urchins are all in this clade C. This is a sister clade to the Chordates D. They are all deuterostomes 5

6 Now onto population ecology. Population a group of organisms of one species occupying a geographic location at the same time, such that they can potentially interbreed. Habitat the physical location where members of a population live. Community all of the organisms in a given habitat. Ecology the study of the relationships among organisms and the environment. 6

7 a. Random Population density the number of individuals of a species per unit area or unit volume of habitat. Different distribution patterns: Random evenly distributed resources, no territories; Uniform evenly distributed resources, strong territories; Clumped unevenly distributed resources. 7

8 Population dynamics is the... Study of the factors that influence changes in a population s size: Immigration the movement of individuals into a population; and Emigration migration out of a population. Births and deaths affect this too, duh! 8

9 Growth rates are affected by... Birth rate the number of new individuals produced per unit time. And... Age structure the distribution of age classes. This determines whether a population is growing, stable, or declining. For example, if a population is mainly of prereproductive age, it will grow; and... If it is mainly of postreproductive age it will remain stable or shrink. 9

10 This can be seen graphically... In population-age pyramids. 10

11 Death rate the number of deaths per unit time. Life table a chart showing the probability of surviving to any given age. 11

12 A survivorship curve is a... Graph of the proportion of surviving individuals at any given age. There are... Three general patterns: Type I invests a great deal of energy and time into their offspring, and mortality is highest as individuals approach their maximum life span; e.g. many large mammals like humans and elephants. Type II there s an equal probability of dying at any age; e.g. many medium sized birds and mammals. Type III produce many offspring but invest little in each one, and most offspring die at a young age; e.g. many fish, and plants, and most invertebrates. 12

13 You can plot this graphically: 13

14 And some of the factors that make it happen... 14

15 Population growth The per capita rate of increase of a population is r. It is the difference between the birth rate and the death rate. If it is negative, the population is shrinking. If it is positive, the population is growing. G = rn This is exponential growth. G is the number of individuals added per unit time. And... N is the number of individuals at the start of a given time interval. 15

16 Exponential growth The number of new individuals is proportional to the size of the population at any given time. A... J-shaped curve emerges. This is... Growth resulting from repeated doubling (exponential). Organisms not native to an area may proliferate exponentially for a time, because there is no natural population controls when they arrive. 16

17 Exponential growth think bacteria in complete (everything they need) media... two, four, eight, sixteen... 17

18 However,... Exponential growth cannot continue indefinitely; something will run out... Environmental resistance the combination of factors that keeps a population from reaching its maximum growth rate. Carrying capacity the maximum number of individuals that a particular habitat can support indefinitely. As a population approaches its carrying capacity, growth slows and eventually stops. 18

19 This makes sense it s called logistic growth and is S- shaped when plotted. See watch? v=nwqnkwwkb4k bad sound, but a good overview. 19

20 G= rn(k-n)/k describes the curve. G is the number of individuals added per unit time. r is the per capita rate of increase. N is the number of individuals at the start of the given time interval. K is the carrying capacity of the population in a particular habitat. rn is the growth rate without limiting resources. N(K-N)/K factors in increasing environmental resistance. However, in reality the carrying capacity is not fixed, e.g. an extended drought may be followed by several wet years. 20

21 There are limits to population size! Density-independent factors exert effects unrelated to population density. These are usually catastrophic, such as... Flood, volcanic eruption, earthquake, severe weather, etc.; versus... Density-dependent factors conditions whose effects increase as a population grows. For example, infectious disease spreads faster in a larger population (makes sense). Competition for space, nutrients, and light can also limit population growth in a densitydependent manner. Ya think.... A population may even crash given limited resources. 21

22 E.g. A population see crashes introduced Reindeer on St. Matthew Island ate up all their food, especially lichen, and then died off. 22

23 Reproductive strategies are called... Life histories all events in a species existence that influence its reproduction. This includes... Whether a species reproduces sexually and/or asexually; its... Life span; its... Age at maturity;... When and how often it reproduces; and... The number and size of its offspring. 23

24 r-selected species: Individuals tend to be short-lived, reproduce at an early age, and have many offspring that receive little care. This is typical of species with a type III survivorship curve. Weeds, crop pests, and many invertebrates are r-selected species. Populations can explode in favorable conditions, but... Density-independent factors tend to limit growth in the long run. 24

25 K-selected species: Individuals tend to be long-lived, late-maturing, and to produce a small number of offspring that receive extended parental care. Therefore, they typically have a... Type I or II survivorship curve. Density-dependent factors, such as competition, limit growth; keeping populations close to their carrying capacity. This is typical of many birds and most large mammals. Both selection strategies are extremes; most organisms fall somewhere in between. 25

26 And remember back... To the first part of the course. Those null-model equations of Hardy- Weinberg and Wright-Fisher, and lots of fancy mathematics, and powerful computer programs, all allow us to... Estimate these sort of population parameters, such as growth, migration, and selection, based on samples of organisms DNA from the populations of interest. 26

27 Told ya it s the big picture that matters. Next... We ll continue to learn about ecology and talk about communities, succession, and ecosystems the foundation of the global biome starting with the tropical rainforest. 27