Bio-diversity, eco-systems and species

http://eos.kub.nl:2080/grnsd/proj/gp-bcfor/cntxt_bio.html (Einblicke ins Internet, 10/1995)

Definition of bio-diversity [16]

Global biological diversity context

Characteristics of threatened populations [16]

Characteristics of threatened eco-systems [16]

Estimated number of species in British Columbia in 1993 [13]

Species officially designated as endangered, 1993 [13]

Species and subspecies at risk in British Columbia, 1993 [13]

One of the better accepted definitions is the biological species concept: A species is a population whose members are able to interbreed freely under natural conditions. Each biological species is a closed gene pool, an assemblage of organisms that does not exchange genes with other species. Thus insulated, it evolves diagnostic hereditary traits and comes to occupy a unique geographic range.

Definition of eco-system [16]

One way of categorizing the biota of Earth is by level of biological organization. The organizational levels of importance to biological diversity are arrayed in this hierarchy:

    Eco-system
        Community
            Guild
                Species
                     Organism
                          Gene

Eco-system - a physical base (e.g. granitic soil weathered from low round hills, streams) plus all the organisms living in that area. The combined physical and biotic elements are tightly bound to one another. Energy is carried as in a leaky bucket from one species to another through the food webs of organisms. Nutrients flow through the organisms, soil, water, and air, and back in unending biogeochemical cycles. The character of the soil cover and water drainage depends intimately on the organisms living thereon. Each eco- system is unique in its particular combination of physical environment and tenant organisms.
Community - all the species connected in the food web and by any other activity that influences the life cycle of the species.
Guild - a set of species that live in the same place and harvest the same food by similar means.
Species - see definition in section above.
Organism - an individual member of a species. Usually considerably less than 30% genetic variation from other individuals in the species.
Gene - a portion of the DNA molecule in an organism. The DNA sequence in a gene determines a particular aspect of the form or functioning of the organism.
Definition of bio-diversity [16]
A complex, but at the same time simple concept. "Biological diversity" refers to the variation in DNA, in genes, in form and function of organisms, species, guilds, communities, and eco-systems which characterises life on Earth.
Bio-diversity is to be valued, if life is valued, for in biological diversity is the embodiment and the only guarantee of continued viability of life. Increased variation yields increased probability of survival, due to increased probability of successful adaptation to the environment.
Note of interest (derived from information in [16])
DNA is flexible and adaptable, but only a vanishingly small fraction of DNA sequences yield viable forms of life. The situation is comparable to the fraction of mathematically possible sequences of letters of the alphabet which yield great works of literature:
Fraction of potential DNA sequences yielding successful adaptations to date:
```
10^8 species x 10^18 DNA variations per species (estimate)
----------------------------------------------------------
4^(10^9)      <-- number of mathematically possible
                  combinations of DNA, given average DNA
                  strand length per organism of 10^9 
                  nucleotide pairs.
```
Global biological diversity context

Estimated total number of species of life [16]

Number of known species of life [16]

Latitudinal bio-diversity gradient [16]

Long-term bio-diversity trends [16]

Historical record of past mass extinction events [16]

The "background" extinction rate [16]

The current extinction rate, 1992 [16]

Estimated bio-diversity loss over next 50 - 100 years (from 1992) [16]

Estimated time required for bio-diversity recovery [16]

Estimated total number of species of life [16]
10 million to 100 million
Number of known species of life [16]
```
Total                                      1,413,000
----------------------------------------------------
Protozoa                                      30,800
Vascular (higher) plants                     248,400
Algae                                         26,900
Fungi                                         69,000
Monera (bacteria & similar forms)              4,800
Viruses                                        1,000
Insects                                      751,000
Mammals                                        4,000
Birds                                          9,000
Reptiles                                       6,300
Amphibians                                     4,200
Fishes and lower chordates                    18,800
Crustaceans, spiders, etc                    123,400
Sponges                                        5,000
Corals, jellyfish, comb jellies, etc           9,000
Flatworms                                     12,200
Roundworms                                    12,000
Earthworms and relatives                      12,000
Mollusks                                      50,000
Starfish and relatives                         6,100
```
Latitudinal bio-diversity gradient [16]
Example: Northern hemispheric gradient in breeding bird species, using land areas of roughly the same size:
```
Greenland             56
Labrador              81
Newfoundland         118
New York State       195
Guatemala            469
Colombia           1,525
```
Long-term bio-diversity trends [16]
Clearly, the very-long-term trend in bio-diversity has been upward, from the beginnings of life 3.5 billion years ago to the present level of 10 million to 100 million species.
However, as shown in the following section, this growth has been punctuated by 5 major dips (mass extinction events), each lasting from 20 to 100 million years. Many more minor dips and rises have characterized the evolution of bio- diversity. (Note: Need to add graphs here.)
Historical record of past mass extinction events [16]
Notes:
1. Figures are for marine animals, because they have left the best fossil record.
2. The Cretaceous extinction is the well-known dinosaur extinction event.
3. Probable cause for all extinctions was long- term climatic change (cooling), except the Cretaceous which is thought to have been a result of a large meteor impact.
4. Time for recovery means time 'til same number of families exist again.
5. Taxonomic unit measured is families (groups of similar species), from the following taxonomic hierarchy, shown with the domestic cat as an example:
```
Species: domestica
  Genus: Felis
    Family: Felidae (all kinds of cats: cheetah, panther, lion, tiger, lynx,...)
      Order: Carnivora
        Class: Mammalia
          Phylum: Chordata
            Kingdom: Animalia

              Time (years       Lost      Lost      Time for
              before present)  Families  Species    Recovery (years)
--------------------------------------------------------------------
Ordovician    440 million      12%                   25 million
Devonian      365 million      12%                   30 million
Permian       245 million      54%       77-96%     100 million
Triassic      210 million      12%                   65 million
Cretaceous     66 million      12%                   20 million
```
The "background" extinction rate [16]
A clade is a species and all its descendants forward through time.
A chronospecies is a species, present for a period of time, which may adapt into one or more later chronospecies. A chronospecies therefore forms the basis of a clade.
Clade longevity, or the rate of clade extinction, is of more significance than chronospecies longevity (or extinction rate), for when a chronospecies disappears, it has sometimes been replaced by one or more evolved successor species.
Clade longevity:
```
Fish and invertebrate clades   1 - 10 million years
Flowering plant clades         1 - 10 million years
Mammal clades                 0.5 - 5 million years
```
The survival and upward trend of life and bio-diversity as a whole depends on the splitting rate of evolving species exceeding the rate at which clades (whole subtrees) die out.
Chronospecies longevity seems to commonly come in at about 1 million years, according to the fossil record.
The general historical "background" chronospecies "extinction" rate, therefore, amounts to 1 species per 1 million species per year, or in absolute terms, multiplied by the current estimated total number of species, the background species extinction rate comes out to between 10 and 100 species per year (including all species such as insects, bacteria etc, not just charismatic mega-fauna.)

The current extinction rate, 1992 [16]
Specifically, in rainforests around the world, a conservative estimate, based on rates of area reduction, yields a current species extinction rate of 27,000 species per year, which is between 1,000 and 10,000 times the background rate.
Estimated bio-diversity loss over next 50 - 100 years (from 1992) [16]
Educated guess of Edward O. Wilson. Edward O. Wilson is Frank B. Baird Jr. Professor of Science and Curator in Entomology, Museum of Comparative Zoology, Harvard University. Some of his books: On Human Nature (Pullitzer Prize), Sociobiology, The Insect Societies, Biophilia, The Ants (Pullitzer Prize), The Diversity of Life. His many scientific awards include the U.S. National Medal of Science and the Crafoord Prize of the Royal Swedish Academy of Sciences.
If natural habitats continue to decline at present rates, estimated 25 % loss of present species.
If we respond with knowledge and technology already possessed, we may hold the loss to 10 % loss of species.
The difference amounts to millions of species.
Human demographic success has brought the world to this crisis of bio-diversity. Human beings - mammals of the 50-kilogram weight class and members of a group, the primates, otherwise noted for scarcity - have become a hundred times more numerous than any other land animal of comparable size in the history of life. By every conceivable measure, humanity is ecologically abnormal. Our species appropriates between 20 and 40 percent of the solar energy captured in organic material by land plants. There is no way we can draw on the resources of the planet to such a degree without drastically reducing the state of most other species.
Estimated time required for bio-diversity recovery [16]
Present trends indicate that a sixth mass extinction event, this one caused by the effects of human population and development, will occur over the next 50 to 100 years.
Prior mass extinctions indicate that bio-diversity will likely recover to present levels (albeit with a different species mix.)
However, the prior extinction events suggest that bio- diversity recovery will take on the order of 20 to 50 million years, or, put another way, about 10 to 25 times longer than humanity has so far existed on Earth.
Characteristics of threatened populations [16]

The area effect

The distance effect

The population size and stability effect

Inbreeding depression

Demographic accidents

Meta-populations

The area effect
As a working ballpark figure, a reduction of 90% in habitat area results in a reduction of 50% in number of species present. The actual relationship follows a known formula with parameters which depend on the particular composition of species in each area and other factors such as the degree of habitat specialization and mobility of species.
The distance effect
The further an island of habitat is from larger areas of habitat and from other islands, the fewer the species will inhabit it.
The population size and stability effect
A "population" is loosely defined as a set of randomly interbreeding individuals of a species. A population is usually constrained to a particular geographic area. As one would intuitively expect, experiment bears out that the smaller the average population size of a given species through time, and the more the size fluctuates from generation to generation, the sooner will the population drift all the way down to zero and go extinct.
Inbreeding depression
Below an effective population size of about 50 breeding individuals, the increased match-up of lethal and sublethal recessive genes slows population growth.
Below an effective population size of about 500 breeding individuals, the mutation rate is not high enough to compensate for loss of genes through genetic drift (chance fluctuation of gene percentages in the population.) The effect is a gradual loss of the ability of a species to adapt to changing environments.
Demographic accidents
The size of the population and the manner by which it is subdivided and spread across the terrain is a more important consideration in the death of a species than the genetic effects of small populations. A species with few and small populations is vulnerable to "demographic accidents" - irregular and drastic reductions in populations caused by environmental change. (E.g. fire, disease, a killing freeze, food species extinction, pollinator extinction etc.)
Meta-populations
"Only a few species consist of a single vulnerable population in one locality. In some cases, the constituent populations are so isolated from one another that they can never exchange individuals, but more typically the species is arrayed as a meta-population, a population of populations, among which organisms do occasionally migrate.
Watched across long stretches of time, the species as meta- population can be thought of as a sea of lights winking on and off across a dark terrain. Each light is a living population. Its location represents a habitat capable of supporting the species. When the species is present in that location the light is on, and when it is absent the light is out. As we scan the terrain over many generations, lights go out as local extinction occurs, then come on again as colonists from lighted spots reinvade the same localities. The life and death of species can then be viewed in a way that invites analysis and measurement. If a species manages to turn on as many lights as go out from generation to generation, it can persist indefinitely. When the lights wink out faster than they are turned on, the species sinks to oblivion.
The meta-population concept of species existence is cause for both optimism and despair. Even when species are locally extirpated, they often come back quickly, provided the vacated habitats are left intact. But if the available habitats are reduced in sufficient number, the entire system can collapse. All the lights go out even if some intact habitats remain. A few jealously guarded reserves may not be enough. When the number of populations capable of populating empty sites becomes too small, they cannot achieve colonization elsewhere before they themselves go extinct. The system spirals downward out of control, and the entire sea of lights turns dark."
Characteristics of threatened eco-systems [16]

Keystone species
In communities, there are little players and big players, and the biggest players of all are the keystone species. As the name implies, the removal of a keystone species causes a substantial part of the community to change drastically. Many other species decline to near or total extinction or else rise to unprecedented abundance.
The sea otter is a keystone species. When it was almost hunted to extinction on the west coast of North America by the end of the 19th century, sea urchins, prey of the otters, consumed the formerly abundant kelp beds. Large stretches of the shallow ocean floor were reduced to a desert-like terrain, called sea-urchin barrens.
A conservation effort restored the otter populations. The kelp forests grew back to their former luxuriance. A host of lesser algal species moved in, along with crustaceans, squid, fishes, and other organisms. Gray whales migrated closer to shore to park their young in breaks along the kelp edge while feeding on the dense concentrations of animal plankton.
Estimated number of species in British Columbia in 1993 [13]
These figures include both forest and non-forest land. However, since a comparatively large fraction of British Columbia has been forested for 10,000 years or so, a similarly large fraction of the species listed are forest- dwelling species, although the exact breakdown is not given here.
Numbers given are for native species, with species introduced recently by people listed in parentheses.
```
Vascular (higher) plants             2,022 (557)
Lichens                              1,000
Fungi                               10,000
Mosses, Liverworts                   1,000
Mammals                                131  (12)
Birds                                  440  (14)
Amphibians                              18   (2)
Reptiles                                15   (4)
Insects                             35,000
Sharks, Bony fish, Lampreys            452  (18)
```
Extirpated Species [13]
Defined as species known to have existed in British Columbia until very recently, but now a population no longer exists in B.C.
```
Vascular plants                         29
Freshwater fish                          1
Amphibians                               1
Reptiles                                 2
Birds                                    4
Mammals                                  7
```
Species officially designated as endangered, 1993 [13]
In British Columbia,
Four species: The burrowing owl, white pelican, sea otter, and Vancouver Island marmot.
Species and subspecies at risk in British Columbia, 1993 [13]
Definitions:
Red = Candidate for legal designation as endangered or threatened under the B.C. Wildlife Act
Blue = Sensitive or vulnerable species
The "% of existing" column gives the percentage of species and subspecies which are at risk, as a percentage of the total number of native species. This is a very slight overestimate, due to the small number of subspecies included in the "at risk" figures. To get an idea how many subspecies were included, consider that a separate figure was given in [13] that there are 702 species (of 732 species and subspecies) on the red list. The blue list was not broken into species and subspecies but a good guess is that the ratio is similar. If this is the case, then the total "at risk" percentage is closer to 37 %.
```
                     Red List      Blue List  |  Total   |  % of existing
----------------------------------------------|----------|---------------
Vascular plants        638           217      |   855    |     42  %
Freshwater fish         28             7      |    35    |      ?
Amphibians               4             2      |     6    |     33  %
Reptiles                 4             5      |     9    |     60  %
Birds                   33            55      |    88    |     20  %
Mammals                 25            27      |    52    |     40 %
----------------------------------------------|----------|---------------
Total                  732           313      |  1045    |     38 %
```
The single most important factor affecting wildlife in B.C. is habitat loss. [13]