<P> A third explanation, known as the portfolio effect, compares biodiversity to stock holdings, where diversification minimizes the volatility of the investment, or in this case, the risk of instability of ecosystem services . This is related to the idea of response diversity where a suite of species will exhibit differential responses to a given environmental perturbation . When considered together, they create a stabilizing function that preserves the integrity of a service . </P> <P> Several experiments have tested these hypotheses in both the field and the lab . In ECOTRON, a laboratory in the UK where many of the biotic and abiotic factors of nature can be simulated, studies have focused on the effects of earthworms and symbiotic bacteria on plant roots . These laboratory experiments seem to favor the rivet hypothesis . However, a study on grasslands at Cedar Creek Reserve in Minnesota supports the redundancy hypothesis, as have many other field studies . </P> <P> There are questions regarding the environmental and economic values of ecosystem services . Some people may be unaware of the environment in general and humanity's interrelatedness with the natural environment, which may cause misconceptions . Although environmental awareness is rapidly improving in our contemporary world, ecosystem capital and its flow are still poorly understood, threats continue to impose, and we suffer from the so - called' tragedy of the commons' . Many efforts to inform decision - makers of current versus future costs and benefits now involve organizing and translating scientific knowledge to economics, which articulate the consequences of our choices in comparable units of impact on human well - being . An especially challenging aspect of this process is that interpreting ecological information collected from one spatial - temporal scale does not necessarily mean it can be applied at another; understanding the dynamics of ecological processes relative to ecosystem services is essential in aiding economic decisions . Weighting factors such as a service's irreplaceability or bundled services can also allocate economic value such that goal attainment becomes more efficient . </P> <P> The economic valuation of ecosystem services also involves social communication and information, areas that remain particularly challenging and are the focus of many researchers . In general, the idea is that although individuals make decisions for any variety of reasons, trends reveal the aggregative preferences of a society, from which the economic value of services can be inferred and assigned . The six major methods for valuing ecosystem services in monetary terms are: </P>

Which elements listed below threaten our marine ecosystem quizlet