Ecological Values
The ecological interactions that are the basis of ecosystems are absolutely fundamental to life. Try to imagine a planet where dead things did not decompose, where water was not filtered through forests, or where plants did not replenish oxygen. Consequently, it is not really profound or insightful to say that ecosystems have ecological value. Nevertheless, it is extraordinary how often we try to place the well‐being of humanity over the well‐being of the ecosystems on which our lives ultimately depend.
Do all ecosystems have equal ecological value? No. Obviously, a large salt marsh will usually provide more ecological values than a small salt marsh, and, similarly, a dominant type of ecosystem such as spruce–fir forests will have more total ecological value than an uncommon type of ecosystem such as caves. Certain types of ecosystems may have a significantly greater importance to other nearby ecosystems than we would predict based on their area. We can call these keystone ecosystems, analogous to using the term keystone species for species with disproportionately significant ecological roles (Chapter 3; deMaynadier and Hunter 1997). The long narrow shorelines where aquatic and terrestrial ecosystems intersect are an excellent example of this (Fig. 4.7). Keystone ecosystems can also shape disturbance regimes that affect large areas by either inhibiting or facilitating the spread of a disturbance. To take two examples: a river can inhibit the spread of a fire, while certain types of woodlands that burn easily can facilitate the spread of fires to other ecosystems. Some of these keystone ecosystems are very small but have effects over large areas, for example, a cave that harbors a wide‐ranging colony of bats or a small pool that provides essential water for animals in a sizable landscape (M.L. Hunter 2017 ; Hunter et al. 2017; see Fig. 4.4).
Figure 4.7 The narrow riparian zones that border river shores are far more important ecologically, to both terrestrial and aquatic ecosystems, than you would predict given their narrow footprint. Thus they can be considered keystone ecosystems within a landscape. This is particularly evident in deserts where river shores are often a ribbon of green in an arid environment.
(Coconino National Forest/Public domain)
Strategic Values
From the perspective of maintaining biodiversity at all levels – genes, species, and ecosystems – the single most essential value of ecosystems may be their strategic value. Conservation biologists have often proposed that by protecting a representative array of ecosystems, most species and their genetic diversity can be protected as well (Hunter 1991; Beier et al. 2015a). This idea is often described using a metaphor of coarse filters and fine filters first proposed by The Nature Conservancy (1982) (Fig. 4.8). The coarse‐filter approach to conserving biodiversity is appealing because it is efficient and provides broad protection. It is efficient because, compared with the number of species in the world, there are relatively few different types of ecosystems and thus protecting a representative array of these is comparatively straightforward. It is broad because it will protect, to some degree, little‐known species such as invertebrates and fungi, even undescribed species, plus their genetic diversity. The Nature Conservancy (1982) originally estimated that 85–90% of species could be protected this way, although this seems optimistic based on the few empirical tests that have been undertaken (e.g. MacNally et al. 2002; Grantham et al. 2010).
Figure 4.8 The strategic value of ecosystems is illustrated by the coarse‐filter–fine‐filter approach to conserving biodiversity. Protecting a representative array of ecosystems constitutes the coarse filter and may protect most species. However, a few species will fall through the pores of a coarse filter because of their specialized habitat requirements or because they are overexploited. These species will require individual management, the fine‐filter approach. In this example, a coral reef ecosystem with all of its constituent species is protected by the coarse‐filter approach, but fine‐filter management is still required for the hawksbill turtle and spiny lobster.
Importantly, the coarse‐filter approach can be an effective strategy regardless of whether ecosystems are tightly connected systems or loose assemblages of species (Fig. 4.3). It is only necessary that the distribution of species and their habitats have some degree of concordance so that a complete array of ecosystems will harbor a reasonably complete array of species (Hunter et al. 1988; Rodrigues and Brooks 2007). We will return to this point and the coarse‐filter approach in general in Chapter 11, “Protecting Ecosystems.” Finally, it is notable that some ecosystems are analogous to flagship species; that is, they elicit public concern about conservation writ large. Tropical rain forests and coral reefs are perhaps the best examples of this phenomenon, but others, such as traditional agricultural ecosystems with high cultural value, are emerging as a new emblem for biodiversity conservation (Chapter 14, “Conservation near People”).
Uniqueness Values
The process of ecosystem classification clouds the issue of ecosystem uniqueness. If we define many different types of ecosystems, each type of ecosystem will not be very different from similar types. Alternatively, if we make gross distinctions (e.g. all coniferous forests are one type of ecosystem), then each type of ecosystem will clearly be unique. Some types of ecosystems may seem unique under any classification, for example, caves and hot springs, but there is a danger of confusing uniqueness and rarity. In short, different ecosystems may have different uniqueness values, but these will be difficult to evaluate until the classification schemes currently being developed are widely accepted. Nevertheless, some types of ecosystems, such as those found on remote islands and dominated by endemic species, are widely acknowledged as unique (Fig. 4.9 depicts one example).
Figure 4.9 The forests of Socotra, a small remote island, could be said to constitute a unique type of ecosystem because they are dominated by endemic species, notably the dragon’s blood tree pictured here.
(Ovchinnikova Irina/Shutterstock)
Ecosystem Diversity and Species Diversity
The coarse‐filter–fine‐filter metaphor (see Fig. 4.8) captures the strategic value of protecting ecosystems as a vehicle for maintaining species diversity, but the relationship between ecosystem‐level conservation and species‐level conservation is more complex than this.
