Interactions between human behaviour and ecological systems
E. J. Milner-Gulland
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Department of Life Sciences, Imperial College London
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Silwood Park Campus, Buckhurst Road, Ascot SL5 7PY
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UK
Research on the interactions between human behaviour and ecological systems tends to focus on the direct effects of human activities on ecosystems, such as biodiversity loss. There is also increasing research effort directed towards ecosystem services. However, interventions to control people's use of the environment alter the incentives that natural resource users face, and therefore their decisions about resource use. The indirect effects of conservation interventions on biodiversity, modulated through human decision-making, are poorly studied but are likely to be significant and potentially counterintuitive. This is particularly so where people are dependent on multiple natural resources for their livelihoods, when both poverty and biodiversity loss are acute. An inter-disciplinary approach is required to quantify these interactions, with an understanding of human decision-making at its core; otherwise, predictions about the impacts of conservation policies may be highly misleading.
1. INTRODUCTION
The theme of this issue of the journal is predictive
systems ecology. However, in order to be truly
predictive in any human-altered environment, the system
under consideration must include human users, and
this requires the integration of ecology with social
science. In this paper, I focus on the potential for
closer integration of ecology and social science in
order to improve the predictive power of system
dynamics models. I draw my examples primarily from
conservation science, with an emphasis on guiding
the implementation of policies aimed at improving the
sustainability of natural resource use.
Traditional ecological studies addressing the effects
of human activities on ecosystems include a body of
literature on the sustainability of direct resource
exploitation, and other major literatures on the effects
of by-products of human activity, such as pollution,
habitat destruction and climate change. The
overexploitation literature has moved in recent years from
a concern with the sustainability of particular levels
of harvest mortality, in terms of the population
trends of the species being harvested, to a wider
concern about ecosystem effects of harvesting, and a
more nuanced understanding of the heterogeneity of
harvesting effects between species and locations.
For example, much work in the 1970s focused on
how best to manage fisheries to maintain stocks
above a target level [1,2]. Broadening the scope to
multi-species fisheries, in the 1990s, authors such as
Roberts [3] highlighted the phenomenon of fishing
down the food chain such that smaller species at
lower trophic levels appeared in the catch as larger
predatory fish were depleted. Nowadays, the
ecosystem approach to fisheries management is embedded
in national legislation (e.g. the USAs Magnuson
Stevens act; [4]) and the challenge is to operationalize
this concept [5,6].
At the broader scale, there is increasing attention to
predicting the effects of human activities on
biodiversity and on particular species groups, difficult
because of the likely threshold or nonlinear nature of
their response to stressors. For example, climate
models predict that the Amazon rainforest is likely to
suffer substantial and rapid die-back beyond a climate
threshold [7,8], while there is a threshold pH beyond
which marine organisms are unable to sequester
calcium for their exoskeletons from seawater [9].
Meta-population persistence is also a threshold
process depending on the size, quality and
configuration of habitat patches [10]. Different processes
may lead to different abundance trends for the species
concerned, some more linear than others [11].
The ecosystem services research field takes the
other side of the equationhow do changes in natural
systems feed through to changes in human well-being
(as defined by the Millenium Ecosystem Assessment
(MEA) [12])? Several steps are required in order to
quantify this contribution; firstly, there needs to be
an understanding of how changes in human activities
impact the dynamics of ecosystems, then how these
changes in ecosystem structure, function and diversity
affect the range of services that humans use and then
how changes in these services feed through into
well-being. The metrics at each stage are not
straightforward to define and the processes involved are not
easy to quantify [13]. This is a very active area of
research, following the lead of the MEA [14]. Few
people have followed the chain of reasoning right
through from changes in management to changes in
well-being, with a rare example being Black ([15];
figure 1). She asked land managers in the UKs
North Pennines Area of Outstanding Natural Beauty
how they would respond to various scenarios of
change, including changes in government policy and
economic circumstances. For example, in one
scenario, consistently low income (...truncated)