|BIODIVERSITY IN EUROPE
What is biodiversity? 3
Genetic Diversity 6
The problems of small populations 7
Species Diversity: Number of species 15
Measurements of biodiversity 16
Indicator group of organism. 17
Higher taxon richness 20
The distribution of biodiversity 22
Flora: distribution patterns 26
Fauna: distribution patterns 30
How to measure the endemism? 40
Ecosystem Diversity 42
Different landscape 49
Biodiversity and Conservation Biology 62
Causes of extinction: habitat destruction 63
Habitat fragmentation 67
Case Study: Songbirds 70
Keystone species 72
Flag-ship species 73
Umbrella species 77
Biodiversity and climate change 78
WHAT IS BIODIVERSITY?
All life on earth is part of one great, interdependent system. It interacts with, and depends on, the non-living components of the planet: atmosphere, oceans, freshwaters, rocks, and soils. Humanity depends totally on this community of life of which we are an integral part. It is the blanket term for the natural biological wealth that undergirds human life and well-being.
The word biodiversity appeared for the first time in 1988. It seems reasonable to ask if it is just a new linguistic bottle for an old wine; a changed fashion label designed to attract funding or does it refer to a new and fundamental question in science?
Biodiversity consists of the variety of life on earth.
Biological Diversity -- or "biodiversity" -- is the totality of genes, species, and ecosystems in a region. The wealth of life on earth today is the product of hundreds of millions of years of evolutionary history. Over the course of time, human cultures have emerged and adapted to the local environment, discovering, using, and altering local biotic resources. Many areas that now seem "natural" bear the marks of millennia of human habitation, crop cultivation, and resource harvesting. The domestication and breeding of local varieties of crops and livestock have further shaped biodiversity.
Why conserve Biodiversity?
Biodiversity is the base of the stability and sustainable function of natural systems.
It has an enormous wide range for potential and unexplored uses.
There is evidences that a removal of ecosystem components can have a negative impact.
Variety is interesting and attractive.
Biodiversity can be divided into hierarchical categories -- genes, species, ecosystems -- that describe quite different aspects of living systems and that scientists measure in different ways. So we can recognise four different categories:
1- Genetic Diversity
2- Species Diversity.
3- Ecosystem Diversity.
Biodiversity can be described in a series of interacting levels (molecular, genetic, population, species, community, habitat and ecosystem diversity). How are these related? Genetic diversity plays a vital role both in the evolutionary processes that create diversity, and in utilisation by man as crops, domestic animals, pharmaceuticals and biotechnological sources. Species diversity is of course central to many ideas of biodiversity.
The genetic variation between individuals arises because these last have slightly different forms of their genes, the units of the chromosomes that code for specific proteins. These slightly different forms of a gene are known as alleles, and the differences can arise through mutations -changes that occurs in the deoxyribonucleic acid (DNA) that constitute an individual chromosomes. The various alleles of a gene may produce forms of protein that differs in structure an function.
The amount of genetic variability in a population is determined by both the number of genes that have more that one allele (polymorphic genes) and the number of alleles for each polymorphic gene. The existence of a polymorphic gene allows individuals in the population to be heterozygous for the gene, that is, to receive two different alleles of the gene from their two parents.
Thus the genetic variability within a population can be measured as:
1- The number (and %) of genes in the population that are polymorphic (have more than one allele).
2- The number of alleles for each polymorphic gene.
3- The number (and %) of genes per individual that are polymorphic.
Until recently, measurements of genetic diversity were applied mainly to domesticated species and populations held in zoos or botanical gardens, but increasingly the techniques are being applied to wild species.
Genetic diversity may be measured also indirectly using electrophoresis (http://www.fst.rdg.ac.uk/courses/fs460/lecture3/lecture3.htm).
Genetic distance formulae The most commonly used is the Nei's standard genetic distance
When genetic diversity is important for biodiversity.
1- In small population.
2- Analysing the genetic differentiation between populations of the same species.
3- In conservation biology problems.
The problems of small populations
A typical metapopulation is characterised by one or more core populations, with fairly stable numbers, and several satellite areas with fluctuating populations; these last may go extinct in unfavourable years, but the areas are recolonized by migrants from the core population when conditions became more favourable.
Genetic variability is important in allowing populations to adapt to a changing environment. In small populations allele frequencies may change from one generation to the next simply due to chance (genetic drift). When an allele is at low frequencies in a small population, it has a significant probability of being lost in each generation (bottleneck effect). The case of Ovis canadensis is very famous since this species has been followed for up to 70 years
Small populations lose much of their genetic variability. The percentage of polymorphic genes in isolated populations of the tree Halocarpus bidwilli in the mountains of New Zealand is a sensitive function of population size.
One of the chief obstacles to a successful species recovery program is that a species is generally in serious trouble by the time a recovery program is instituted. When populations become very small, much of their genetic diversity is lost. The black rhino is highly endangered, living in 75 small, widely separated populations. Only about 2400 individuals survive in the wild. Many of these small populations may not be viable as a result of inbreeding depression, genetic deficiencies resulting from mating among closely related individuals.
The example of cheetah (Acinomyx jubatus).
Before last glaciation the five species of cheetah were distributed in Asia, Africa and North America. During glaciation (100,000 years ago) four species extinguished and the last were limited to parts of Africa. Actually only 5,000 individuals are living, with a strong reduction of fertility and a young mortality of 70%. The researchers have find that only the 3,2% of genes studied are polimorphic.
This example demonstrates the the genetic diversity lost is lost forever.
Evolutionary relationships between populations.
It is interesting to study the distribution of intraspecific biodiversity.
For example in freshwater fishes they have demonstrated that the genetic diversity is much lower at higher latitude, particularly in areas glaciated during Pleistocene cold periods where extensive postglacial recolonization occurred.
The following fig. shows the maximum extension of the ice sheet in North America and in Europe during the last cooling, about 20,000-18,000 years ago. Thus plants and animals have experienced, during the last 2.5 m.y., some dramatic changes in geographic distribution due to climatic shifts. In temperate regions of the northern hemisphere, most of the species remain in southern refugia during cold periods in relation to the extinction of northern populations, and expanded towards north during subsequent warmings.
The philogeography of 10 taxa, including mammals, amphibians, arthropods and plants were compared to elucidate general trends across Europe. During glaciation almost all taxa survived in these refuges: Spain, Italy and Balkans (R1, R2, R3).
The northern regions were colonised generally from the Iberian and Balkan refugia; the Italian lineage were often isolated by Alpine barrier. The right fig. shows the suture zones, that is where different populations of the same species encounter themselves after a postglacial expansion.
Two example of intraspecific genetic studies: the brown trout (Salmo trutta) and the bullhead (Cottus gobi)
The figure shows the 4 refuges and the postglacial colonisation routes the brown trout.
Number of species
Species Diversity. Species diversity refers to the variety of species within a region. Such diversity can be measured in many ways, and scientists have not settled on a single best method. The number of species in a region--its species "richness"--is one often-used measure, but a more precise measurement, "taxonomic diversity," also considers the relationship of species to each other. For example, an island with two species of birds and one species of lizard has greater taxonomic diversity than an island with three species of birds but no lizards. Thus, even though there may be more species of beetles on earth than all other species combined, they do not account for the greater part of species diversity because they are so closely related. Similarly, many more species live on land than in the sea, but terrestrial species are more closely related to each other than ocean species are, so diversity is higher in marine ecosystems than a strict count of species would suggest.
Some authors have proposed a number of 1.4 million species of living forms, others 30 millions of insects alone. Wilson has calculated a loss of species from the tropical area alone could be as high as 6,000 species per year and the tropical forest cover only the 6 % of the land surface area of the earth.
MEASUREMENTS OF BIODIVERSITY
Intuitively, we understand biodiversity, or species diversity, as the number of species in a given area, habitat, or community. However, the formal treatment of the concept and its measurement is complex. A biodiversity index characterizes the diversity of a sample or community by a single number. The concept of "species diversity" involves two components: the number of species, or richness, and the distribution of individuals among species, or evenness. For example, consider two tree stands, A and B, each with a total of 100 trees belonging to ten species. Stand A includes 91 trees of one species and one tree of each of the other nine species. Stand B includes 10 trees of each of the ten species. While the species richness of the two stands is the same (ten species), Stand B is typically considered more "diverse" than Stand A, as the 100 trees are evenly distributed among the ten species.
We discuss the following widely used biodiversity indices:
Species Richness (S).
The simplest measurement of species diversity is a species count. Simple species counts remain the most popular approach to evaluate species diversity and to compare habitats or species assemblages. While species counts are often an early step in many ecological and community studies, the number of species per se provides little insight into the underlying ecological mechanisms that define biodiversity, nor does it encompass evenness.
Shannon-Weaver Index (H).
Perhaps the most widely used index of species diversity is the Shannon-Weaver Index:
H = - (the sum of Pi ln Pi) for i = 1 to S
i is the ith species
P is the proportion of the total number of individuals or biomass
S is the total number of species
This index considers both the number of species and the distribution of individuals among species. For a given number of species S, the largest value of H results when every individual belongs to a different species. However, comparisons among communities or habitats based on H are possible only if the sample size is the same.
Simpson Index of Diversity (D).
Another frequently used diversity index, Simpson index of diversity, measures the sum of the probabilities that two randomly chosen individuals belong to the same species, summed over all species in the sample:
D = 1 / (the sum of Pi2) for i = 1 to S
i is the ith species
P is the proportion of the total number of individuals or biomass
S is the total number of species
The value of D varies widely as the total number of species increases, depending on the type of species-abundance relationship used to calculate the index.
Simpson's index is a commonly used dominance measure, because it is weighed towards the abundances of the commonest species rather than providing a measure of species richness.
Since the total number of species is difficult to valuate they use different strategies.
Indicator group of organism.
Since the number of species is very often too large, is possible to use only some indicator group of organism.
Here, increasing intensity of green is used to represent increasing species richness of butterflies in the first map and increasing intensity of blue is used for species richness of birds in the second map. The geographical patterns of diversity for two groups of organisms can be compared graphically by overlaying the two maps in two separate colours. These green and blue maps are then overlaid in the third map. Consequently, black grid cells on the third map show low richness for both butterflies and birds; white shows high richness for both; and shades of grey show intermediate and covarying richness for both (these covarying scores lie on the diagonal of the colour key, to the left of the third map).
This technique allows relationships between groups to be compared visually at a broad range of spatial scales. Within Britain, for example, any gross differences in the strength of the overall national relationship can be judged from the overall colour saturation of the map; second, any regional deviations from this national relationship can be seen in regional colour trends; and third, local deviations can be seen as isolated spots of differing colour.
More strongly divergent patterns between some groups have long been known to natural historians. There is a negative correlation between the distribution of species richness of Pinaceae (pines, firs, spruces, larches) and the richness of Fagaceae (oaks, beeches and chestnut).
Here, increasing intensity of blue is used to represent increasing native species and subspecies richness of Pinaceae and intensity of green is used for native species and subspecies richness of Fagaceae. In this case an indicator relationship would not be expected, because the two groups tend to have preferences for different climates. Many of the Pinaceae are a dominant component of the Boreal forests of northern and eastern Europe (blue), whereas the Fagaceae are a major component of the Southern-temperate forests of southern and western Europe (green). Nonetheless, in central Europe many species of the two groups occur in close proximity in the mountains (white or red: for example, on the southern side of the Alps), although often at different altitudes.
The most time there is also a correlation between two different taxonomical groups, for example between insects versus vascular plats.
Higher taxon richness
Several studies support the idea of a relationship between the numbers of higher taxa, such as families, and the numbers of species among areas.
Genera or families has been suggested to be useful as a surrogate for species richness. In comparison with the method of using small indicator groups of species, it should have an advantage of precision for predictions if it permits a broader coverage of the groups of organisms surveyed.
In the absence of direct counts of plant species richness, in this example they have counted the numbers of seed plant families (from a total of 395) to represent relative variation in the numbers of species (from a total of c. 300,000) expected. See the precedent fig and compare with this one.
THE DISTRIBUTION OF BIODIVERSITY
Large-Scale Gradients of Species Diversity
Since before Darwin, biologists have recognised that there are more different kinds of animals and plants in the tropics than in temperate regions. For many species, there is a steady increase in species richness from the arctic to the tropics. Called a species diversity cline, such a biogeographic gradient in numbers of species correlated with latitude has been reported for plants and animals, including birds, mammals, reptiles.
Why are there more species in the tropics?
The most commonly discussed suggestions:
It has often been proposed that the tropics have more species than temperate regions because the tropics have existed over long and uninterrupted periods of evolutionary time, while temperate regions have been subject to repeated glaciations. The greater age of tropical communities would have allowed complex population interactions to coevolve within them, fostering a greater variety of plants and animals in the tropics. However, recent work suggests that the long-term stability of tropical communities has been greatly exaggerated. An examination of pollen within undisturbed soil cores reveals that during glaciations the tropical forests contracted to a few small refuges surrounded by grassland. This suggests that the tropics have not had a continuous record of species richness over long periods of evolutionary time; unfortunately, the fossil record is too sparse to assess the past species richness of the tropics.
A second often-advanced hypothesis is that the tropics contain more species because this part of the earth receives more solar radiation than temperate regions do. The argument is that more solar energy, coupled to a year-round growing season, greatly increases the overall photosynthetic activity of plants in the tropics. If we visualise the tropical forest as a pie (total resources) being cut into slices (species niches), we can see that a larger pie accommodates more slices. However, many field studies have indicated that species richness is highest at intermediate levels of productivity. Accordingly, increasing productivity would be expected to lead to lower, not higher, species richness. Perhaps the long column of vegetation down through which light passes in a tropical forest produces a wide range of frequencies and intensities, creating a greater variety of light environments and in this way promoting species diversity.
There are no seasons in the tropics. Tropical climates are stable and predictable, one day much like the next. These unchanging environments might encourage specialisation, with niches subdivided to partition resources and so avoid competition. The expected result would be a larger number of more specialised species in the tropics, which is what we see. Many field tests of this hypothesis have been carried out in the tropics, and almost all report larger numbers of narrower niches.
Many reports indicate that predation may be more intense in the tropics. In theory, more intense predation could reduce the importance of competition, permitting greater niche overlap and thus promoting greater species richness.
As noted earlier, spatial heterogeneity promotes species richness. Tropical forests, by virtue of their complexity, create a variety of microhabitats and so may foster larger numbers of species.
Diversity in Homogeneous Habitats
Not all species diversity can be explained by factors such as those responsible for clines in species diversity. Over 40 years ago the great ecologist G. E. Hutchinson pointed out that freshwater lakes support hundreds of species of algae, even though theory then predicted that the number of species should not exceed the number of resources for which they compete. They couldn't be competing for hundreds of different resources in this very homogeneous habitat, so the source of diversity seemed a mystery. Ecologists have since proposed four major solutions to this paradox, each of which can easily account for the observed diversity. The challenge has been to figure out which of the four explanations is actually responsible for the high diversity often seen in homogeneous habitats in nature. The four diversity-generating mechanisms
suggested by theory are:
Spatial heterogeneity. A habitat that appears homogeneous to us may not in fact appear so to the species involved. Heterogeneity in microclimate or other factors not obvious to an observer could easily generate high levels of diversity.
Trophic interactions. Interactions among species of several different trophic levels (at least three) can produce high levels of diversity because of the complex forms the interactions may take. For example, plants, their herbivores, and parasites of plants and herbivores can produce many different patterns of competition and predator-prey interactions, all presenting opportunities for evolutionary diversification.
Periodic disturbance. A pattern of intermittent episodic disturbance that produce gaps in the rainforest (like when a tree falls) allow invasion of the gap by other species. Eventually the species inhabiting the gap will go through a succession sequence, one tree replacing another, until a canopy tree species comes again to occupy the gap. But if there are lots of gaps of different ages in the forest, many different species will coexist, some in young gaps, others in older ones.
Flora: distribution patterns
The flora of Europe comprises 10-12.000 species. Their abundance is linked to many and complex factors: climate, altitude, environment (dunes, rock, prairies), substrata (alkalinity-acidity), humidity, latitude, ground texture, wind, sun exposition, etc.
Some examples give an idea of the different kinds of distribution patterns.
Fauna: distribution patterns
The vertebrate fauna of Europe comprises one thousands species (3.6% of the world species). It is a little number considering Europe represents 6.8 of the world surface area.
There is an increasing number of species from North to South.
We compare three different countries: Spain, France and Sweden.
Spain, which was a refuge during glaciation, has 66% of European vertebrates, France 64%, Sweden, separated by an isthmus from Europe, only 39%.
Endemic species is a species which is only found in a given region or location and nowhere else in the world. This definition requires that the region that the species is endemic to, be defined, such as a “site endemic”, a “national endemic” (e.g. found only in Honduras), a “geographical range endemic” (e.g. found in the Himalayan region).