Plate 1.1.

Diagram of the interaction of factors influencing amphibian decline. Arrows point from the influencing factor to the affected attribute. Double-headed arrows indicate that both factors interact, each having an effect on the opposite one. Arrows of different shades indicate that the influencing factor can either enhance (black arrows) or inhibit (grey arrows) the effect, depending on circumstances. The diagram is simplified in several ways. Some ovals list only general categories of influences (e.g. groups of chemicals, rather than individual chemicals). A more detailed flow chart would list the individual chemicals separately, but would be impossible to chart. Also, such items as herbicides and insecticides are manufactured and hence could be linked to ‘manufacturing’, but rather are linked to ‘agriculture’, which is the activity that applies the chemicals. Similarly pharmaceuticals are manufactured but are not linked to manufacturing, because the diagram would become unduly cluttered. Note that the effect of ‘pet trade’ and ‘food, research, medicine’ on diseases is via trade in infected animals that serve as vectors (mainly of chytridiomycosis). Some of the arrows are of direct links; others subsume a cascade of links. For example, the single arrow linking herbicides with amphibian decline is a composite of direct and indirect links. The direct one is the effect of some herbicides on the development and survival of amphibian larvae; the indirect one is the effect of herbicides on algae that form the diet of amphibian larvae. Many of these links could be expanded in this way, each forming a new flowchart. Perhaps a useful exercise would be to number each arrow in this figure and then compile a series of sub-flowcharts, each relating to a numbered arrow. An atlas of such diagrams would allow sequential assessment of multifaceted interactions. More detailed flowcharts of some particular segments have already been published for amphibians, such as global climatic change and amphibian decline (Burrowes 2009), relationships among stressors, organismal responses, and population performance (Rohr et al. 2009), effects of pesticides on amphibian declines (Hayes 2005; Boone et al. 2009) and on the mechanisms of endocrine disruption (McCoy and Guillette 2009), as well as the negative impacts of contaminants on larvae (Bridges and Semlitsch 2005). CFCs = chlorofluorocarbons (used as refrigerants, aerosol propellants, and solvents); DOC = dissolved organic compounds; PCBs = polychlorinated biphenyls (used as coolants, insulating fluids, and flame-retardants); UV = ultraviolet radiation. Colour codes to types of causes or influences: Purple = primary causes (note that all of these are anthropogenic); green = ecological factors; yellow = chemical factors; blue = physical factors; brown = physiological factors; grey = developmental factors. Modified and reprinted with permission from Heatwole (2013).