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few years to keep yields up at a commercially viable level and reduce likelihood of
losses due to disease or pests. This keeps external inputs high and limits the ecosystem benefits that could be provided by a purely perennial crop. Grains and nitrogenfixing plant species such as legumes—which require less external nitrogen fertilizer
inputs because they are able to use atmospheric nitrogen or N 2 more directly—are
the types of plants most frequently pursued in conceptual alternatives to resourceintensive agriculture. Better understanding is needed about potential candidate species and the selection process that could be used for their adaptation to widespread
cultivation.
9.2.3.2 Animals
Animal-plant interactions play important roles in ecosystems and agriculture, both
beneficial and detrimental. The primary roles animals play in plant survival, reproduction and fertilization are as pests, herbivores, pollinators, and decomposers; secondary roles are played as control-agents for pest species, and in the formation of
soil structure that can help water to be retained rather than being lost from the soil.
In some cases, highly specific interactions between a host plant and its associated
pollinator species require both the animal and the plant in order for both to survive
and reproduce.
Animals themselves may be agents of both ecosystem disturbance and maintenance. For example, large migratory ungulates on grassland, such as buffalo in the
USA and elephants in Africa, were long thought to be contributors to over-grazing
and loss of grassland productivity. As more research has been done on the complex
ecosystem dynamics driven by animals, the need for maintaining spatial heterogeneity and placing limits on human landscape modifications such as fenced boundaries and artificial water sources have emerged as more important factors that prevent
animals from adhering to natural limits on carrying capacity.
9.2.3.3 Microorganisms
Although animals such as insects may play similar roles to microorganisms in
below-ground ecosystems, bacteria and fungi are the most powerful and relatively
unseen mediators of these ecosystem processes. As discussed in relation to
biogeochemical cycles, soil structure, and soil–biological interactions, these
microorganisms play essential roles that include retaining water, cycling nutrients, and supporting plant growth. Without fungi, we would have neither the
decomposition required to break down nutrients into more available forms to support plant growth, nor the creation of important food products using yeast (a unicellular fungus).
On the less beneficial side, bacteria and fungi also represent some of the most
economically important diseases of agricultural plants and animals and destroyers
of agricultural products. Additionally, to the extent that fuel wood is attacked by fungi,
N. Matthews et al.
few years to keep yields up at a commercially viable level and reduce likelihood of
losses due to disease or pests. This keeps external inputs high and limits the ecosystem benefits that could be provided by a purely perennial crop. Grains and nitrogenfixing plant species such as legumes—which require less external nitrogen fertilizer
inputs because they are able to use atmospheric nitrogen or N 2 more directly—are
the types of plants most frequently pursued in conceptual alternatives to resourceintensive agriculture. Better understanding is needed about potential candidate species and the selection process that could be used for their adaptation to widespread
cultivation.
9.2.3.2 Animals
Animal-plant interactions play important roles in ecosystems and agriculture, both
beneficial and detrimental. The primary roles animals play in plant survival, reproduction and fertilization are as pests, herbivores, pollinators, and decomposers; secondary roles are played as control-agents for pest species, and in the formation of
soil structure that can help water to be retained rather than being lost from the soil.
In some cases, highly specific interactions between a host plant and its associated
pollinator species require both the animal and the plant in order for both to survive
and reproduce.
Animals themselves may be agents of both ecosystem disturbance and maintenance. For example, large migratory ungulates on grassland, such as buffalo in the
USA and elephants in Africa, were long thought to be contributors to over-grazing
and loss of grassland productivity. As more research has been done on the complex
ecosystem dynamics driven by animals, the need for maintaining spatial heterogeneity and placing limits on human landscape modifications such as fenced boundaries and artificial water sources have emerged as more important factors that prevent
animals from adhering to natural limits on carrying capacity.
9.2.3.3 Microorganisms
Although animals such as insects may play similar roles to microorganisms in
below-ground ecosystems, bacteria and fungi are the most powerful and relatively
unseen mediators of these ecosystem processes. As discussed in relation to
biogeochemical cycles, soil structure, and soil–biological interactions, these
microorganisms play essential roles that include retaining water, cycling nutrients, and supporting plant growth. Without fungi, we would have neither the
decomposition required to break down nutrients into more available forms to support plant growth, nor the creation of important food products using yeast (a unicellular fungus).
On the less beneficial side, bacteria and fungi also represent some of the most
economically important diseases of agricultural plants and animals and destroyers
of agricultural products. Additionally, to the extent that fuel wood is attacked by fungi,
N. Matthews et al.