1. BIOTIC DIVERSITY IS HUGE, COMPLEX, & AND MULTI- DIMENSIONAL

• kinds of organisms,
• numbers of organisms,
• how organisms are distributed in time,
• how organisms are distributed in space.

Our key to comprehending all this complexity is the recognition that:
 

The evolutionary process involves both

• the generation of myriad new forms - diversification -
• and their adaptation to conditions through natural selection.
 
you may find out more about these processes by clicking here or here

Some of the conditions to which life adapts are:

• those provided by the physical characteristics of the planet itself (such as how continental drift has altered geography)
• the interactions between the planet and the biota, involving life's products (such as the level of oxygen in the atmosphere)
• the interactions among the various organisms themselves - competition, predation etc.

2. what kinds of organisms are there?

•  form = what do they look like?   see 3. below

•  function = what do they do? how do they live?  see 5. below

•  type = which are their closest relatives?  see 6. below

3. organismal form

sizes range from:
 

•  bacteria at 0.1 micrometres (10^-7 m.)

 through
•  protists at ~100 micrometres (10^-4 m.)

 and
•  most insects & vertebrates at ~1 cm. to ~1 m.

 to
•  the largest animals (~10m.) & plants (~100m.)

4. the primary dimensions of organismal structureinclude:

• cellular internal structure - prokaryote vs. eukaryote

 
• single- vs. multi-cell organization

 
• level of differentiation in multicell organisms -the degree of tissue & organ development.

5. how organisms live - their biological functioning -

•  how do they get their food?
-inorganic (e.g. a plant) or organic (e.g. a cat) sources
•  how do they get their energy?
-sunlight, or the breakdown of chemical compounds
•  where do they do all this?
-there are organisms virtually everywhere - ocean deeps to highest mountains & deep into the crust;
- where organisms live influences how they can get their food & energy

6. the major groupings of  types of organism - what is usually called biological classification -

are based on their inferred closeness of  EVOLUTIONARY RELATIONSHIPS - the recency of their common ancestors.

Traditionally, this involved consideration of characteristics of gross form & of function, and, not long ago, most organisms were considered to be either:

but now, through the use of tools such as the electron microscope and DNA/RNA sequence analysis, we have access to a more diverse set of characteristics, and their careful analysis has revealed a different & clearer picture of the evolutionary relationships among life's forms -

Below is a figure showing the evolutionary relationships among all of earth's biota. Identified there are the five kingdoms (the Bacteria or Monera turn out to include two distinctive clusters of forms - here referred to as Bacteria and Archaea).

Note the diversity of UNfamiliar forms as compared to the closeness of the forms with which we are most familiar.

See also L.N. 1.5 showing the development of eukaryote structure from prokaryotes by endosymbiosis.

7. what is the numerical composition of the biota?

the answer depends on what kinds you count: species; families; classes; phyla..............  most species are insects

 Here are some pie-diagrams which induicate the ways in which the various groups break down by sumbers of species.  For further detail, please see the Lecture notes, Chapter 8.
 

First , we have a representation of the relative numbers of species so far known to science in each of the five kingdoms.  The tiny number of described bacteria (Monera) and the small number of known fungi almost certainly is a serious underestimate of the numerical importance of these groups. Note the apparent predominance of the Animal kingdom.

Here we see the species breakdown for the Animal Kingdom alone.  Within this kingdom, the overwhelmingly abundant group are the insects which number approximately one million species. Note how numerically unimportant the vertebrates appear.

Focussing down onto the vertebrates, we find that nearly one half of all species are bony fish.  Next in importance are the birds, followed by reptiles.  Our own group, the mammals, are relatively insignificant numerically. If we were to focus down closer, onto the species composition of the mammals, we would see that our own group, the Primates are really insignificant, with only 4% of species.  Mammals are strongly numerically dominated by rodents, bats and insectivores, in that order, which together provide over 70% of mammalian species.

Altogether, we see that the earth's biota is dominated by life forms with which most of us are not familiar.  Our own kind does not provide a good yardstick for taking the true measure of life on earth.

8. how has organismal diversity changed through time ?

• earth's biota has become more diverse overall - there more kinds of organisms now than at earlier times.

 
• its composition has changed - there are kinds living now that did not exist before;  there are kinds that lived once, but are now extinct, and we know of them as fossils.

 
• these changes represent the net product of the proliferation & extinction of evolutionary lineages

First we see the marine record, which includes a diversity of unfamiliar animals, many now extinct, along with a good number which are still around today.  Notice the rapid growth of the biota during the Cambrian and Ordovician periods, then a more or less steady-state until the end of the Permian (about 250 m.y.a.).  At that time there took  place the greatest extinction the world has eyt experienced.  SInce that time, the marine fauna has become progressively more diverse up to the present.

Next we see the vertebrate record, which largely includes forms familiar to most of us.  Until mid-Devonian, all vertebrates were aquatic, but slowly, terrestrial forms diversified, spectacularly so in the Mesozoic (Triassic, Jurassic & Cretaceous);  this was the time of the rise of the reptiles.  Birds, bony fish and mammals originated back in the Triassic and Jurassic, but began an enormous rise to their present prominence at the end of the Cretaceous, coinciding with the end of the dinosaur dominance of terrestrial habitats.

9. evolutionary time is vast

a football field of paces takes us back to the start of agriculture;

a walk from Fairbanks, Alaska to Miami, Florida would take us to the origins of multicellular life;

a great-circle flight from N.Y. to Perth, Australia would take us to the origins of eukaryotes

TO REACH LIFE'S ORIGINS would take us past N.Y, and most of the way back to Perth again.
 

Another way to gain some impression of the vastness of time, especially as compared to the times with which we have some familarity, is to represent all the time since earth's origins in a circle, and break that circular pie into segments according to their durations:
 
 

To put this figure in some perspective, recall that the Age of Dinosaurs is the Mesozoic Era, lasting from about 250 million to 65 million years ago;  mammals did not come to dominate the terrestrial world until the Cenozoic, starting about 65 m.y.a. Humans did not arise diverge from other apes until the last few m.y.a.;  modern Homo sapiens has only been around for 1-200,000 years.  Such times could not be represented on this figure - the lines separating the periods shown are approximately 8 million years think!

 To expand upon this initial picture, see pp. 8 & 9 in Introductory materials and the detailed Time-charts.

10. how is life's diversity arrayed in space? (and why?)

•  type - where are the various evolutionary lineages?  see 11 & 12 below

 
•  number - where is most biotic diversity?  see 13 below

 
•  form & function - what & where are life's different adaptive forms?  see 14 below

11. life's lineages are unique in space & time

therefore, where they are now depends on where & when they originated  and how the global geography has changed since then ..............

Our understanding of the earth's past geography has changed radically in recent time, leading to a greatly-improved understanding of the geographical distribution of organisms.

12. over the last 30 years, we have learned in detail how the earth's crust has slowly drifted about the globe

their passenger biotic lineages thus may evolve, depending on circumstances,

at times in isolation, when they have undisputed access to some restricted part of the globe;

at other times they may gain access to wider geographic areas and become exposed to other evolving lineages

these opportunities for protected diversification and/or expansion + competition lie behind some profound irregularities in the geographical distribution of kinds of organisms.  This is the topic of biogeography.

see L.N. 11.4, 5 & 6, showing continental drift and biogeographic realms.

For further description of the basics of organismal geography, click here.

On the net, see this excellent site, which provides a series of plate-tectonic reconstructions to show the broad patterns of Phanerozoic Earth history (the last 600 million years or so).

13. where most diversity is in the world

in this course we shall look simply atpatterns in 'species richness' -the number of species in any given group in any specified region

species richness depends on both the geographical location and the size of the region.

In general, species richness increases towards the equator:

 species richness is also positively related to the area considered.

It is not simply a matter of latitude or area, however;  it is also profoundly affected by rainfall, among other things.........      see L.N. 8 & 9.

14. aspects of climate are implicated both in biotic richness and adaptive form

what are the qualitative, evolutionary-adaptive responses of the biota to climate?

we find that, to some extent, the different evolutionary lineages that are found in the different continental regions respond in similar adaptive ways to major features of global climate which may span several continents, generating  major adaptive assemblages recognised as biomes.

These biomes are recognisable as such because the general appearance of their prominent organisms is very much the same, even though those organisms often derive from very different evolutionary lineages.

Biomes include such major assemblages as arctic tundra, boreal forest, deserts, grasslands and rainforests.

This system of BIOMES is the final global biotic pattern which we shall illustrate.

 see L.N. 12 for global climate, and the rest of the Lecture Notes for the ways that the biota responds to it.