We need to understand the stresses affecting the conservation targets - as distinct from sources of stress
- in order to ensure that we develop effective conservation and threat abatement strategies. While the distinction
is often confusing, it will actually make a complex task - prioritizing threats to biodiversity - easier to understand.
TNC's Practioner's Handbook for SCP provides an excellent example, taken from Beyond the Ark by Bill Weeks,
p. 46.
By considering "Threats" as two more narrowly defined steps:
...project teams would be better positioned to develop good strategies. Team members are now advised to ask first what the ecological stresses to a system are - independent of the source of those stresses - before separately tracing those stresses to their sources. For example [we] call a proposed road a threat in an estuarine system. We are then immediately inclined to the conclusion that we must stop construction of the road. Threat: road. Solution: stop road. However, if we separate the threat into stress and source, the stress isn't the road. The stress is, for example, loss of tidal flow. That formulation of stress inclines us to think, instead, of ways to keep tidal waters flowing through the pathway that is the proposed location of the road. Culverts may be the answer."
To develop further the above example, let's imagine that hunting of waterfowl occurs at a small scale in the estuarine system, but the proposed road will greatly increase hunters' access. The stress to waterfowl population viability might include a change in demography such that mortality rates exceed reproductive rates or altered stage structure of the population (e.g., which stage class in the population is most conspicuous and preferentially hunted: juvenile/subadults, adult males displaying to attract females, nesting females). The source of stress, the road which facilitates hunter access, may be built as a slightly-elevated flyway so that vehicles may not go off-road.
To summarize, stress is the impairment or degradation of the size, condition, and landscape context of the target, and results in the reduced viability of the target. A source of stress is an extraneous factor, either human or biological, that infringes upon a conservation target in a way that results in stress. Where this distinction becomes valuable is when stress to the target originates from multiple sources or when a single source causes stress to multiple targets. The next page explains stress analysis in more detail.