ZOOLOGY 224: LECTURE 1
1. Introductions
2. Review of syllabus, textbooks, policies
3. Goals of the course
a. To appreciate the diversity of past and present animal life on Earth
b. To understand the general architecture of ancient and present animal communitie
c. To understand the functional morphology of ancient and especially present animal groups
d. To understand the processes of evolution and extinction that give rise to the diversity of lineages of ancient and present faunas
4. Over half a billion years growing the tree of life -- the major groups of organisms that we will treat in this course and their ancient derivation (see handout and text)
5. How many groups (ie, taxa [plural; taxon singular]) such as phyla, classes, orders, families, genera, and species [plural; species singular] are there?
Information on the number of described species changes constantly. The following gives you an approximate idea of how many described species there are in different groups of living organisms (what is important here is for you to know the "ballpark number" of some of the major groups and the total). We discussed in class that these represent only a small fraction of the total (known plus unknown) species on Earth; estimates of the total (described and undescribed) number of species on Earth range from 10-100 million. The scientific concensus in the last several years is converging on an estimate of about 15-20 million total species on Earth. If about 2 million are described (below), then about 10-15% of all species have been described so far. Notice that described insects constitute about 50% of all known described species, that marine organisms comprise only about 275,000, fresh water organisms about 45,000, and symbiotic (parasites, etc.) about 100,000 species, in contrast to about 1.5 million terrestrial species. Part of this is because terrestrial environments are better known than these other environments.
DESCRIBED SPECIES DIVERSITY OF MAJOR GROUPS OF LIVING ORGANISMS
(from Reaka-Kudla, 1997, The Global Biodiversity of Coral Reefs: A comparison with Rainforests, in M. L. Reaka-Kudla, D. E. Wilson, and E. O. Wilson, Biodiversity II: Understanding and Protecting Our Natural Resources)
See Handout
Although many more terrestrial than aquatic species have been described (above, especially insects), many more higher level taxa (e.g., phyla) are known from aquatic than terrestrial environments; in particular, there are many more phyla that live only in the sea (endemic) than in other environments (see below). These phyla include many of the invertebrate phyla that we will study in this course
HIGHER TAXONOMIC DIVERSITY OF MARINE VS. TERRESTRIAL ENVIRONMENTS
(From Reaka-Kudla, 1997, ibid)
See Handout
6. How does this diversity arise? What processes (microevolution, macroevolution) explain the diversity we see around us now and in ancient times?
The essential elements of Evolution include the following ideas. a-d are included in our concepts of microevolution; e-f are included in our concepts of macroevolution. Both evolutionary processes are essential for understanding the biodiversity we see in the world.
a. There must be heritable (capable of being inherited) variation among different individuals in the population that is passed down from parent to offspring.
b. Many more offspring are produced than survive and reproduce themselves; the offspring's survival and reproduction usually are not random relative to the traits that differ among them
c. Therefore some genotypes are passed on to future generations more frequently than others
d. Barriers to reproduction (physical, geographical, behavioral, physiological) among individuals with different traits result in genetic shifts and eventually divergence of species.
As examples of microevolution, we talked about Darwin's observations of how finches had diverged on the different Galapagos Islands, the divergence of the bills of Hawaiian honeycreepers, and the divergence of the terminal populations of salamanders in a circle or horseshoe shpaed range that included the Coast Range and the Sierras, so that when the two terminal populations came into contact with each other in the south they could no longer interbreed.
e. Some lineages persist for very long periods with little observable change (called "stasis") while other lineage diverge suddenly and rapidly. This is called "punctuated equilibrium".
f. Extinction may wipe out entire lineages, allowing diversification of others.
These larger scale processes, usually observed in the fossil record, are called macroevolution. We examined changes in configuration of the continents over the last half billion years as related to changes in global biodiversity. Factors that have been implicated in diversification include (i) provinciality, (ii) climatic stability, (iii) environmental complexity, and all of these are related to the configuration of the shifting continents (see handout with diagram and read handout on changes in biota over the geological periods; know the general patterns of how animal and plant communities changed from the Paleozoic to Mesozoic to Coenozoic; remember that all of the major phyla were already formed by the beginning of the Paleozoic). Lastly we discussed the process of extinction and its influence on the global biota (see handout). Note that there have been many mass extinctions (we will talk about how these affected individual phyla as we pass through these phyla during the course); the greatest mass extinction of all time occurred at the end of the Paleozoic; another notable one occurred at the end of the Mesozoic, resulting in the loss of the dinosaurs as well as many other groups.