Study Design and Logistics - Wetland Techniques - page 10

in flooded forests and suggested testing a more complex interaction between
subsidy and stress factors.
Use of predictive hypotheses led Collins and Storfer ( 2003 ) to categorize six
hypotheses potentially explaining global amphibian declines into two classes. Class
I hypotheses were those in which underlying ecological mechanisms affecting
amphibians were well known, but the relativemagnitude of the effects was uncertain;
these were presence of alien species, over-exploitation, and land use change.
For Class II hypotheses, there was a poor, but increasing understanding of the
relative effects on amphibian populations; these were global changes in UV
radiation and climate, contaminants, and emerging infectious diseases. They
concluded that additional research using integrated approaches was necessary
to understanding all of the complex interacting predictions of the hypotheses.
One can retrospectively test competing hypotheses by compiling results from
previous studies. van der Valk ( 2012 ) reviewed theories and multiple hypotheses
relative to invasive plant species in wetland systems. There are two principal theories
for why so many invasive plants are found in wetlands: (1) wetlands are more
vulnerable to invasion because they are landscape sinks and susceptible to disturbance
and (2) invasive species are superior competitors. Numerous hypotheses and
associated predictions have been advanced within the two theories (e.g., enemy
release, hybrid vigor, empty niche). Following a review of the evidence, van der
Valk ( 2012 ) concluded that while there is some support for the superior competitor
theory, hypotheses based on landscape sink/disturbance theory had the most support
for explaining the presence of invasive plant species in wetlands.
The key to development of a study design is the ability to conclusively reject a
hypothesis (or several hypotheses) such that the scientific process can progress. To
test the efficient-community hypothesis (all plant species that can become
established and survive under the environmental conditions found at a site will
eventually be found growing there and/or will be in its seed bank) for restored
wetlands, Galatowitsch and van der Valk ( 1996 ) compared the floristic composition
of natural and restored wetlands in northern Iowa. Although a few similarities were
found between natural and restored wetlands, they rejected the efficient-community
hypothesis with a conclusion that dispersal ability of plants had a greater influence
on recolonization of plants in restored wetlands than site-specific presence.
In wetland science, theories and hypotheses are not restricted to ecological
concepts. For example from an economic perspective, Whitten and Bennett
( 2005 : 45) proposed a theoretical concept that “the production of wetland protec-
tion outputs is unlikely to be at the level desired by the community,” which
essentially means that society values wetlands at a level greater than that being
provided by conservation efforts. They formulated two basic hypotheses that could
be tested by an appropriate study: (1) “an increase in the production of wetland
protection outputs would generate a net benefit to the community” and (2) “policies
in alternative to those currently in place would reduce the extent of market or
government failure in the protection of wetland production outputs” (Whitten and
Bennett 2005 : 46-47). From an archaeological viewpoint, Kelly and Thomas
( 2012 ) outlined competing hypotheses for human presence in the Carson Desert,