BIODIVERSITY IN
EUROPE
Daniele Bedulli
CONTENTS
Page
What is biodiversity?
3
Genetic Diversity
6
The problems of small populations 7
Phylogeography
12
Species Diversity: Number of species
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
Endemism
33
How to measure the endemism?
Ecosystem Diversity
42
Different landscape
49
Biodiversity and Conservation Biology
Causes of extinction: habitat destruction
Habitat fragmentation
67
Case Study: Songbirds
70
Keystone species
72
Flag-ship species
73
Hotspots
75
Umbrella species
77
Biodiversity and climate change
Bibliography
79
15
40
62
63
78
WHAT IS BIODIVERSITY?
Overview
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.
Genetic Diversity
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.
Phylogeography
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.
Species Diversity
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 Southerntemperate 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:
Evolutionary age.
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.
Higher productivity.
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.
Predictability.
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.
Predation.
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.
Spatial heterogeneity.
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 diversitygenerating 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 (alkalinityacidity), 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%.
ENDEMIS
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).