Social Ecological Systems, Humans as Key Ecosystem Components
Humans are a major force in global change and drive eco system dynamics, from local
environments to the entire biosphere. At the same time, human societies and global
economies rely on ecosystem services. As such, human and natural systems can no longer
be treated independently because natural and social systems are strongly linked.
Accumulating evidence suggests that effective environmen tal management and
conservation strategies must take an integrated approach, one that considers the
interactions and feedbacks between and within social, economic, and ecological systems.
As a result, the concept of coupled ‘social–ecological systems’ has become an emerging
focus in environmental and social science and ecosystem manage ment. Social–ecological
systems are considered as evolving, integrated systems that typically behave in nonlinear
ways.
The concept of resilience – the capacity to buffer change – has been increasingly used as
an approach for understanding the dynamics of social–ecological systems. Two useful
tools for building resilience in social–ecological systems are struc tured scenario modeling
and active adaptive management. Models of linked social–ecological systems have been
developed to inform management conflicts over water quality, fisheries, and rangelands.
These models repre sent ecosystems coupled to socioeconomic drivers and are explored
with stakeholders to probe the management deci sion making processes. Alternative
scenarios force participants to be absolutely explicit about their assumptions and biases,
thereby improving communication between sta keholders and exposing the ecological
consequences of various management policies.
Adaptive management is an approach where manage ment policies themselves are
deliberately used as experimental treatments. As information is gained, poli cies are
modified accordingly. This approach helps isolate anthropogenic effects from sources of
natural variation and, most importantly, considers the consequences of a human
perturbation on the whole ecosystem. In contrast, basic research on various parts of an
ecosystem leads to the challenge of assembling all the data into a practical framework.
Yet, biotic and abiotic ecosystem components are not additive, they interact. Due to these
interactions, the dynamics of an ecosystem cannot be extrapolated from the simple
addition of an ecosystem’s components.
Adaptive management examines the response of the sys tem as a whole rather than a
sum of its parts. Furthermore, this approach involves adaptive learning and adaptive
institutions that acknowledge uncertainties and can respond to nonlinearities. In sum,
structured scenario modeling and policy experimentation are tools that can be used to
examine the resilience of social–ecological systems to alternative management policies
and conserva tion strategies.
Pollination Services Provided by Bees
Pollination, the movement of genetic material in the form of pollen grains, is a key step in
the development of most food crops. Even crops that do not rely on insect pollination –
wind pollinated or self pollinated crops – are sometimes more productive when visited by
an insect pollinator. Bees are a particularly important group of insect pollinators,
responsible for pollinating 60–70% of the world’s total flowering plant species, including
nearly 900 food crops worldwide, such as apples, avocados, cucum bers, and squash.
These crops comprise 15–30% of the world’s food production, and bees are credited with
$4.2 billion in annual crop productivity in California alone. Bees are especially important
pollen vectors in part because physical adaptations, such as hairs designed to pick up
pollen, and behavioral adaptations, such as fidelity to a single species of plant on each
pollen gathering trip, ensure good pollen transport and cross pollination.
In the US, most major agricultural enterprises that rely on bee pollination import managed
bees, almost always the European honeybee Apis mellifera. The available stock of
managed honeybees has declined dramatically, how ever, dropping by over 50% in the
last 50 years, while demand for pollination services has increased in many areas. This
decline in managed bee populations has many causes, including increased pesticide use,
disease in the hives, and downsizing of stocks that have hybridized with Africanized bees,
introducing traits that make managed bees more aggressive and thus a liability to the
farmer.
The contribution of native, wild bees to agricultural pollination was ignored, and assumed
to be negligible, until the early 2000s. Since then, research has shown that native bees
serve an important role in pollination, picking up slack when managed bee pollination is
insufficient and enhancing crop production in general. Farms with generous native bee
habitat nearby may be able to fully or partially replace pollination by managed bees. In
some cases, native bees are more efficient polli nators than European honeybees. The
variety of wild bees, with distinct physical and behavioral traits, allows them, as a group,
to pollinate a wide variety of flowering plants. Tomatoes, for example, have pollen that is
acces sible only by vibrating the flower, which bumble bees and some other native bees
can, while honeybees cannot.
Though tomatoes are self pollinating and do not require an insect vector, native bees
promote cross pollination, which, for example, significantly increases the fruit set and size
of Sungold cherry tomatoes. The contributions of native bees to crop production are
usually undocumented and underestimated, and they are always unpaid, at least directly.
Though hives of managed honeybees must be rented or maintained, wild bees pollinate
at no cost to the farmer. Populations of native bees are under great threat, however, by
land management practices that promote the use of pesticides and the loss,
fragmentation, and degradation of habitat. Protecting native bees without protecting the
ecosystems in which they live is impossible. Native habitat, unlike agricultural
monocropping, provides the year round sup ply of blooming plants that wild bees require
for sustenance. Native habitat also provides nesting areas; most wild bees are solitary,
laying a single egg in a nest cavity dug into the ground or into dead wood, not forming
social hives. In order to reap the benefits of native polli nators, food resources and nesting
habitat must be available within a short distance of crops, possibly as hedgerows, in
ditches, or around water ponds.
A study of wild bee pollination of coffee in Costa Rica showed that farms closer to tropical
forest remnants were visited by many more species of wild bees than those further away.
Had the far sites been adequately pollinated, coffee yield would have been increased by
nearly 20% and misshapen coffee beans reduced by 27%. A lower bound estimate of the
pollination services from these patches is US $62 000 per year (in the early 2000s).
The diversity of the native bee population is one of its strengths. Many species of bees
participate in pollination, and the abundance of different species varies year by year. This
diversity allows the native pollinator community to be both resistant, maintaining
functionality in the face of environmental upheaval, and resilient, able to reestablish itself
in the wake of a destructive event. When the popula tion of Apis declined dramatically in
the second year of the Costa Rica study, sites close to forest fragments showed minimal
loss of pollination while pollinator visits dropped by nearly 50% further away. Thus, as
well as enhancing pollination services in conjunction with managed bees, native bee
populations provide important insurance against
