Ecological Niches 113phosphate accumulated in corn that is fed to cattle ends up
in feedlot wastes, or in human wastes when people consume
beef. These phosphates may eventually cause water quality
problems in rivers, lakes, and coastal areas. For practical pur-
poses, phosphorus that washes from the land into the ocean
is permanently lost from the terrestrial phosphorus cycle, for
it remains in the ocean for millions of years. Also, the addi-
tion of excess phosphorus from fertilizer or sewage can con-
tribute to undesirable enrichment of water and land, as il-
lustrated in the chapter-opening story on Lake Washington.- What are the differences and similarities
among the five biogeochemical cycles,
particularly in the roles organisms play
in them?
water, where it is available for aquatic producers to use
again.
Phosphate can be lost from biological cycles. Some
phosphate is carried from the land by streams and rivers
to the ocean, where it can be deposited on the seafloor
and remain for millions of years.
A small portion of the phosphate in the aquatic food
web finds its way back to land. A few fishes and aquatic
invertebrates are eaten by seabirds, which may defecate
on land where they roost. The manure of seabirds, called
guano, contains large amounts of phosphate and ni-
trate. Once on land, these minerals may be absorbed by
the roots of plants. The phosphate contained in guano
may enter terrestrial food webs in this way, although the
amounts involved are small.
Humans affect the phosphorus cycle by accelerating
the long-term loss of phosphorus from the land. Part of the
Ecological Niches
LEARNING OBJECTIVES
- Describe the factors that contribute to an
organism’s ecological niche. - Explain the concept of resource partitioning.
Y
ou have seen that a diverse assortment of
organisms inhabits each community and
that these organisms obtain nourishment in
a variety of ways. You have also considered
energy flow and biogeochemical cycles. Now let’s exam-
ine the way of life of a given species in its ecosystem, how
it fits into its environment and how it uses energy it has
gained. An ecological description of a species typically
includes whether it is a producer, consumer, or decom-
poser. However, we need other details to pro-
vide a complete picture.
Every organism is thought to have its own
role, or ecological niche, within the structure
and function of an ecosystem. The ecological
niche describes the place and function of a
species within a complex system of biotic and
abiotic factors.
An ecological niche is difficult to define precisely be-
cause it takes into account all aspects of the organism’s
existence—all physical, chemical, and biological factors
the organism needs to survive, remain healthy, and re-
produce. Among other things, the niche includes the lo-
cal environment in which an organism lives—its habitat.
An organism’s niche also encompasses what it eats, what
organisms eat it, what organisms it competes with, and
how the abiotic components of its environment, such as
light, temperature, and moisture, interact with and in-
fluence it. A complete description of an organism’s eco-
logical niche involves numerous dimensions to explain
when, where, and how an organism makes its living.
An organism’s potential ecological niche may be
much broader than it actually is in nature. Put differ-
ently, an organism may be capable of using
much more of its environment’s resources or
of living in a wider assortment of habitats than
it actually does. The potential, idealized eco-
logical niche of an organism is its fundamental
niche, but various factors, such as competition
with other species, usually exclude it from part
of its fundamental niche. The lifestyle an or-
ganism actually pursues and the resources it actually uses
make up its realized niche.ecological niche
The totality of
an organism’s
adaptations, its use
of resources, and the
lifestyle to which it is
fitted.