([a] Olympic National Park/Flickr/Public domain; [b] Hubert/Shutterstock. [c] Procy/Shutterstock)
As a rule, conservation biologists tend to focus more on the population health of keystone species than dominant or controller species because many keystone species are uncommon, whereas, by definition, dominant and controller species are relatively abundant. Of course, being abundant does not mean that these species are necessarily secure from population crashes. Many island plants have gone from being ecological dominants to being far less common following the introduction of exotic herbivores or competitors (Cole and Litton 2014). Even continental species have plunged from dominance to rarity in a short period; such was the case for the American chestnut (once 20% of the trees in eastern North America, now essentially gone) following invasion of an exotic fungus disease. Consequently conservationists should play close attention to all species that are highly interactive, both keystones and dominants, because changes in their populations affect entire ecosystems (Soulé et al. 2003). Indeed, some conservationists use the term “ecological extinction” if a species becomes too rare to fill its role in an ecosystem, a term that applies to many large animal species today (i.e. those that are still present but in greatly diminished numbers, like American bison).
When assessing the ecological roles of species, conservation biologists are typically conservative and assume every component of an ecosystem is important unless proven otherwise (Berlow 1999; Montoya et al. 2006). Our understanding of ecosystems is usually so limited that it is sensible to take this position, even though most species probably do not play irreplaceable roles. Furthermore, it is possible that one should look beyond the role of individual species because overall species richness of an ecosystem may be an important attribute. We will return to this issue in the next chapter, “Ecosystem Diversity.” Finally, it is important to realize that a species that is relatively unimportant now may become more important as an ecosystem changes through time. For example, since the last glaciation some trees species, such as eastern hemlock, have shifted between being ecosystem dominants over large areas and being quite uncommon (Williams et al. 2004).
Incidentally, there are many ways in which ecological values interface with economic values. Most notably, the health and productivity of people have huge economic consequences, and these are directly dependent on ecological integrity. One paper examined the relationship between deforestation by an invasive insect, the emerald ash borer, and human mortality, and suggested that through higher stress, lower air quality, and reduced physical exercise the insect might be linked to an increase of 20,000 deaths across 15 states in the United States (Donovan et al. 2013). Similarly, each species we use directly for economic gain as food, medicine, materials, and so forth depends on ecosystems and the continuing existence of a whole suite of other species.
Strategic Values
With a large agenda and limited resources, conservation biologists have to be efficient strategists, and this often leads them to target certain species – generically often called surrogate species or proxy species –to advance their overall goal of maintaining biodiversity (Caro 2010). Best known are the flagship species, the charismatic species that have captured the public's heart and won their support for conservation (Verissimo et al. 2011; Skibins et al. 2013). Some species have won converts to conservation across the globe; consider the cuddliness of the giant panda, the haunting songs of the humpback whale, and the grandeur of the tiger. Some species have been rallying points for local action, engendering local pride and concern. In northeastern Peru, for example, conservationists built a program around the yellow‐tailed woolly monkey, an endangered species endemic to the area, using special T‐shirts, posters, and other means. Once the local people learned how special their monkey was, it was much easier to enlist their support for conservation of all the local biota (see Case Study 15.1).
Large mammals, especially those with big brown eyes, are often the most successful flagships, but many other species have been successfully used too. In northern Maine an inconspicuous rare plant with an unprepossessing name, Furbish’s lousewort, became a flagship species for the effort that stopped a dam that would have flooded 35,000 hectares of forest. This was a case where concern for an ecosystem pushed a species into the flagship role. A better‐known example of the flagship process in reverse comes from the northwestern United States where concern for old‐growth forests made the spotted owl a flagship species.
Conservationists sometimes focus on umbrella species on the assumption that addressing the habitat needs of a particular species can, under the right circumstances, benefit the habitat of many species, even whole ecosystems, thus making the target species an umbrella for many species. For example, to secure a viable population of snow leopards you will, by extension, have to secure a large population of various species of ungulates – the snow leopard’s prey – and the large mountain and grassland areas those herbivores require to survive, and hence all the plants and smaller animals that also live in such places. Typically umbrella species are relatively large animals and thus many umbrella species are also flagship species. However, the terms are not synonymous because it is their patterns of habitat use, not popularity, that make some species good umbrellas.
Conceptually, umbrella species should have large home ranges, and thus by protecting enough habitat for their populations, adequate habitat for many other species will also be protected. Similarly, if umbrella species are found in a wide variety of ecosystems across a broad geographic range they can provide an umbrella for a very large set of species. The tiger is a classic example (Fig. 3.12). Conservationists have also used the umbrella species concept in other ways with mixed results (Roberge and Angelstam 2004; Branton and Richardson 2011), for example, by conserving habitat specialists that will only generate a small umbrella, or, conversely, by identifying suites of umbrella species to generate a broader umbrella. When using the broad umbrella species concept for such specific applications, the conservation “shortcut” might disappear if the exercise requires detailed information on the habitat needs of co‐occurring species (Seddon and Leech 2008).
Figure 3.12 With a geographic range reaching from the Russian Far East south to Indonesia and west to India (formerly to Turkey and Iran), the tiger ranges across a broad set of ecosystems – boreal forests, mangrove swamps, rain forests, dry deciduous woodlands, riparian thickets, and more. Efforts to keep the tiger from going extinct have benefitted other wild creatures throughout much of Asia thus making it a classic umbrella species.
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Some species are useful to conservation biologists because the health of their populations is an easy‐to‐monitor indication of environmental conditions or of the status of other species; these are called indicator species (Niemi and McDonald 2004). They are the “miners’ canaries” that can warn us about general environmental degradation just as miners used to carry canaries to warn them of poor air quality. The classic example comes from the impact of DDT on peregrine falcons, brown pelicans, and some other birds. DDT caused their eggs shells to thin, resulting in fewer young produced and catastrophic declines of these species. This phenomenon first alerted scientists to a subtle but pervasive and serious impact of DDT and similar compounds for an entire ecosystem and ultimately human health. Smaller species are often sensitive indicators; for example, lichens reflect forest management practices that change a forest’s microclimate (Nascimbene et al. 2013) as well as urban air quality, and aquatic invertebrates are monitored to track water pollution (Sundermann et al. 2013). Some indicator species provide “easy access”; for example,