pertinent to microbial ecology. The exploitation of
resources in a habitat is considered one of the fundamental
factors determining abundance and diversity. “Niche”
defines resource fields in terms of nutrients and space in
particular, in which a species exists. One of the main
paradigms of ecology is that two species cannot occupy
the same niche. Coexistence implies that each organism
has a different niche, even if these niches may overlap. For
many microbial experimental systems, it has been shown
that the coexistence of different species or biotypes of
microorganisms increases when the environment is
structured (as summarized by Jessup et al. 2004). Spatial
structure essentially leads to an increase in the number of
niches, especially in terms of microenvironments. Trophic
relationships between organisms are also considered
important for the overall structure of a community. Primary producers may limit the abundance of heterotrophic
ones, and the complexity of the network can be a buffer
against the collapse of a network if a primary producer
were to disappear. Using macrocosms, laboratory
microbiologists have shown that the length of the food
chain depends on the productivity of primary producers
(Jessup et al. 2004). The term “succession” describes the
changing composition of organisms during the maturation
of a community. Initial colonizers of habitats are named
“pioneer species.” Their presence alters the habitat and
thereby creates new opportunities for others. The succession process in the establishment of forests has been well
described, with herbs, willow (Salix), and nitrogen-fixing
species such as alder (Alnus) and coniferous species
(Pinus, Abies, Juniperus, etc.) colonizing coastal sand
dunes, which are then replaced by deciduous species
(oak, maple, etc.) as organic matter and nitrogen accumulate in the soil and as the growth of large and long-lived
species gradually limits the entry of light into the canopy
(Lichter 1998). Microorganisms play a central role in the
colonization process given the scarcity of nitrogen in most
pioneer-stage terrestrial ecosystems. Thus, during glaciers
retreat, the moraine is first colonized by species (Dryas,
Alnus) that fix dinitrogen in symbiosis with the
actinobacterium Frankia and then give way to climax
species such as spruce or poplar (Lawrence et al. 1967).
Comparable phenomena are described following volcanic
eruptions (Vitousek et al. 1987), landslides, or forest fires
(Yelenik et al. 2013).
Biodiversity of a community is considered a potentially
important element for the functioning of an ecosystem in its
entirety. However, there have been many debates about the
general nature of such causation: Does the ecosystem and its
associated processes determine the level of biodiversity, or
are the functions of the ecosystem the result of the level of
biodiversity (Naeem 2002)? Whatever the cause or effect, a
paradigm is well established that the functioning of
communities and ecosystems and the stability of operation
are strongly related to biodiversity, low-diversity systems
are the most vulnerable, and those with high diversity are the
most robust and resilient. Details of the intense debate on the
relationship between diversity and stability were
summarized by McCann (2000). An example of the role of
diversity in community stability is given by Mitchell and
collaborators (2002) who have highlighted the role of the
level of diversity of grassland plant communities for resistance to fungal diseases. Symptom severity (% leaf area
infected) in monocultures was three times larger than that
observed in diversified prairies. Plant diversity appears to
play a role in limiting the spread of pathogens between
individuals of susceptible species. In plots with intermediate
plant diversity, community composition plays a major role
and compensates for the absence or presence of a particular
species with high or low susceptibility that can have a major
influence on the overall reaction of the community. Regarding microorganisms, microcosms were used to assess the
relationship between diversity and stability. These
microcosms allow good control of physicochemical factors.
Using mixtures of algae, bacteria, protists, and small
metazoans, several authors have shown that the microcosms
with the highest diversity were the most stable in terms of
CO 2 fluxes, for example, and were more resistant to
invasions. The use of microcosms to test such hypotheses
in microbial ecology has been reviewed by Jessup and
collaborators (2004).
There are many other hypotheses about the establishment and structuring of communities. A major contribution to ecological concepts as applied to microbiology
was provided by Kinkel and collaborators (Andrews
et al. 1987; Kinkel et al. 1987a, b, 1989) in their test of
the theory of Island Biogeography. The theory of Island
Biogeography proposed by MacArthur and Wilson (1963)
postulates that the number of species found on an island
(the number at equilibrium) is determined by two factors:
the distance to the mainland and the size of the island.
These two factors affect the rate of extinction* on the
islands and the level of immigration*. For microbiology,
the concept of island is of course relative to the scale of
microorganisms, and it will therefore be applied to
fertile habitats separated by stretches of low fertility.
By sterilizing leaves in an apple orchard, Kinkel et al.
(1987a, b, 1989) created new islands for colonization.
They were also able to estimate the rate of immigration,
emigration, multiplication, and mortality of leaf
colonizers such as Aureobasidium spp. and the plant
pathogen Venturia inaequalis and demonstrate that the
pattern of colonization corresponded to theoretical
predictions.
8 Biodiversity and Microbial Ecosystems Functioning
263
resources in a habitat is considered one of the fundamental
factors determining abundance and diversity. “Niche”
defines resource fields in terms of nutrients and space in
particular, in which a species exists. One of the main
paradigms of ecology is that two species cannot occupy
the same niche. Coexistence implies that each organism
has a different niche, even if these niches may overlap. For
many microbial experimental systems, it has been shown
that the coexistence of different species or biotypes of
microorganisms increases when the environment is
structured (as summarized by Jessup et al. 2004). Spatial
structure essentially leads to an increase in the number of
niches, especially in terms of microenvironments. Trophic
relationships between organisms are also considered
important for the overall structure of a community. Primary producers may limit the abundance of heterotrophic
ones, and the complexity of the network can be a buffer
against the collapse of a network if a primary producer
were to disappear. Using macrocosms, laboratory
microbiologists have shown that the length of the food
chain depends on the productivity of primary producers
(Jessup et al. 2004). The term “succession” describes the
changing composition of organisms during the maturation
of a community. Initial colonizers of habitats are named
“pioneer species.” Their presence alters the habitat and
thereby creates new opportunities for others. The succession process in the establishment of forests has been well
described, with herbs, willow (Salix), and nitrogen-fixing
species such as alder (Alnus) and coniferous species
(Pinus, Abies, Juniperus, etc.) colonizing coastal sand
dunes, which are then replaced by deciduous species
(oak, maple, etc.) as organic matter and nitrogen accumulate in the soil and as the growth of large and long-lived
species gradually limits the entry of light into the canopy
(Lichter 1998). Microorganisms play a central role in the
colonization process given the scarcity of nitrogen in most
pioneer-stage terrestrial ecosystems. Thus, during glaciers
retreat, the moraine is first colonized by species (Dryas,
Alnus) that fix dinitrogen in symbiosis with the
actinobacterium Frankia and then give way to climax
species such as spruce or poplar (Lawrence et al. 1967).
Comparable phenomena are described following volcanic
eruptions (Vitousek et al. 1987), landslides, or forest fires
(Yelenik et al. 2013).
Biodiversity of a community is considered a potentially
important element for the functioning of an ecosystem in its
entirety. However, there have been many debates about the
general nature of such causation: Does the ecosystem and its
associated processes determine the level of biodiversity, or
are the functions of the ecosystem the result of the level of
biodiversity (Naeem 2002)? Whatever the cause or effect, a
paradigm is well established that the functioning of
communities and ecosystems and the stability of operation
are strongly related to biodiversity, low-diversity systems
are the most vulnerable, and those with high diversity are the
most robust and resilient. Details of the intense debate on the
relationship between diversity and stability were
summarized by McCann (2000). An example of the role of
diversity in community stability is given by Mitchell and
collaborators (2002) who have highlighted the role of the
level of diversity of grassland plant communities for resistance to fungal diseases. Symptom severity (% leaf area
infected) in monocultures was three times larger than that
observed in diversified prairies. Plant diversity appears to
play a role in limiting the spread of pathogens between
individuals of susceptible species. In plots with intermediate
plant diversity, community composition plays a major role
and compensates for the absence or presence of a particular
species with high or low susceptibility that can have a major
influence on the overall reaction of the community. Regarding microorganisms, microcosms were used to assess the
relationship between diversity and stability. These
microcosms allow good control of physicochemical factors.
Using mixtures of algae, bacteria, protists, and small
metazoans, several authors have shown that the microcosms
with the highest diversity were the most stable in terms of
CO 2 fluxes, for example, and were more resistant to
invasions. The use of microcosms to test such hypotheses
in microbial ecology has been reviewed by Jessup and
collaborators (2004).
There are many other hypotheses about the establishment and structuring of communities. A major contribution to ecological concepts as applied to microbiology
was provided by Kinkel and collaborators (Andrews
et al. 1987; Kinkel et al. 1987a, b, 1989) in their test of
the theory of Island Biogeography. The theory of Island
Biogeography proposed by MacArthur and Wilson (1963)
postulates that the number of species found on an island
(the number at equilibrium) is determined by two factors:
the distance to the mainland and the size of the island.
These two factors affect the rate of extinction* on the
islands and the level of immigration*. For microbiology,
the concept of island is of course relative to the scale of
microorganisms, and it will therefore be applied to
fertile habitats separated by stretches of low fertility.
By sterilizing leaves in an apple orchard, Kinkel et al.
(1987a, b, 1989) created new islands for colonization.
They were also able to estimate the rate of immigration,
emigration, multiplication, and mortality of leaf
colonizers such as Aureobasidium spp. and the plant
pathogen Venturia inaequalis and demonstrate that the
pattern of colonization corresponded to theoretical
predictions.
8 Biodiversity and Microbial Ecosystems Functioning
263