Four factors merit special attention when they are known to occur in an ecosystem slated for repair: (1) microhabitats, (2) mutualistic symbiotic relationships, (3) endemic species, and (4) rare species. Years ago, while working in the shrub-steppe ecosystem of southeastern Oregon, I became fascinated with the microhabitats created by large anthills and their thriving populations. The most striking aspect of this community, however, was the distinctive microclimate it created, which was especially noticeable in early spring.
As the snow melted, it did so on the south-facing slopes of the anthills, which left the north-facing slopes bedecked in snow. Once the snow was gone, the south-facing slopes warmed and were graced with early-spring vegetation, such as bur buttercups, whereas the north-facing slopes remained frosted or even frozen at times. As well, the ant’s activities, from sunning themselves to foraging, occurred on the south-facing slopes and remained thus restricted until the sun’s warmth more evenly affected their immediate environment.
A somewhat similar situation, particularly with respect to grasshoppers, occurs in the Natal Drakensberg Mountains of South Africa, where the hilltops act as thermal refugia from the cold-air drainage of winter. The increased insolation on the eastern and northern sides of the hilltops compared with the western and southern sides is particularly attractive to the grasshoppers. Crevices in the hill summits provide further micro-refugia in a matrix of thermally inhospitable land.1
MUTUALISTIC SYMBIOTIC RELATIONSHIPS
Mutualistic symbiotic relationships need special attention because if one species is lost, so will the other be. For example, birds may hover over or perch on flowers to feed on their nectar, and their doing so cross-pollinates flowers of the same species on other plants when the birds visit them. However, the rat’s tail plant, which is endemic to the South African cape, appears to be unique among bird-pollinated plants in that it has a sterile inflorescence axis whose sole function is to provide a perch for foraging birds. This structure enhances the plant’s reproductive success by causing the malachite sunbird, its main pollinator, to adopt a position that is ideal for pollinating its unusual ground-level flowers.2 This brings me to the importance of endemism per se.
Endemism is an important aspect of biodiversity that is often confined to small, isolated areas or to a severely limited number of species in an area or to both. The species involved are narrowly adapted and thus easily eliminated, and their elimination can have dramatic effects on the ecosystem of which they were a part, as illustrated by three disparate examples in New Zealand, the Balearic Islands of the western Mediterranean, and the central Pyrenees of France.
In New Zealand, two endemic mistletoes have declined considerably since 1840. Their decline is reputedly due to introduced herbivores but is coincident with a major decline in the densities of native birds. As it turns out, bellbirds and tuis are significant pollinators and seed dispersers not only of the endemic mistletoes but also of many other native plants. The continued existence of these mistletoes will require maintenance of native bird populations. A breakdown of such mutualistic relationships may have widespread consequences.3
The introduction of exotic species onto an island can have significant effects on the density of native populations and their distribution, as well as on their ecological and evolutionary feedback loops. Disruptions of this type can be dramatic, significantly reducing the reproductive success of native species and even causing their extinction, as happened on both Menorca and Mallorca islands in the Mediterranean as a result of the introduction of carnivorous mammals.
Prior to the release of carnivorous mammals, two endemic species—a perennial shrub and a frugivorous lizard—served each other’s needs in a mutualistic symbiotic relationship. The Balearic Islands lizard is now extinct, and the shrub, the Balearic Islands Daphne, is in danger of extinction on both Menorca and Mallorca islands. Fortunately, relict populations of both the lizard and the shrub, as well as their mutualism, still exist on a separate, isolated 158-acre islet, where the Daphne is abundant.
The population of Daphne with the greatest seedling recruitment is on the islet, where the lizards remain in abundance. In turn, the lizards appear to be the only dispersers of the shrub’s seeds because they not only consume large amounts of the shrub’s fruits without affecting either germination or seedling growth but also move the seed to sites suitable for the shrub’s establishment. The disruption of such a specialized plant-vertebrate mutualism can set one or both partners on the road to extinction.4
In the central Pyrenees of France, the diversity of springtails, a tiny soil-dwelling insect, was studied at two sites, and a semi-natural beech forest was compared with a conifer plantation at each site. Although differences in the structure and composition of the springtail communities were observed in both the beech forest and the conifer plantation, these changes followed different patterns at the two sites. In both cases, however, the diversity of the springtail community was impoverished in the plantation, where endemic components of the community suffered a particularly severe loss in species richness and abundance. The non-endemic species, however, were less affected. Endemic biota represent the most valuable element in an ecosystem and thus are its most vulnerable component—one whose biological service to the system is seldom understood.5
Although not endemic by definition, rare species can also make significant contributions to the functioning of an ecosystem, but these contributions are often aggregated into data on common species and thus overlooked. In this case, prudence dictates that uncommon species be assumed to make positive contributions to the functioning of the ecosystem wherein they dwell.6
With the foregoing in mind, we would be wise to determine—as best we can—whether an ecosystem we are concerned about is functioning within healthy parameters. If, on the one hand, it is, then the question becomes how to sustain its processes and thus maintain its biophysical integrity. If, on the other hand, the ecosystem appears to be in decline, we need to figure out what action is necessary to mend its structure in order to revive and sustain its processes. In either instance, how do we know whether we are making changes that will lead to our desired outcomes?
Let’s suppose that five prairie remnants are going to be repaired, each of which has a different soil type. It will be critical to the repair to understand how the perennial grasses behave during their recovery from grazing. The healing process is so slow and often subtle, however, that casual observation will not suffice. At this point monitoring becomes important because the process is specifically designed to observe and document subtle ecological changes.
1. Michael J. Samways. Land Forms and Winter Habitat Refugia in the Conservation of Montane Grasshoppers in Southern Africa. Conservation Biology, 4 (1990):375–382.
2. Bruce Andersom, William W. Cole, and Spencer C. H. Barrett. A Plant Scores by Providing an Access Point for Visiting Sunbirds to Feed on Its Nectar. Nature, 435 (2005):41–42.
3. Alastair W. Robertson, Dave Kelly, Jenny J. Ladley, and Ashley D. Sparrow. Effects of Pollinator Loss on Endemic New Zealand Mistletoes (Loranthaceae). Conservation Biology, 13 (1999):499–508.
4. The two previous paragraphs are based on: Anna Traveset and Nuria Riera. Disruption of a Plant-Lizard Seed Dispersal System and Its Ecological Effects on a Threatened Endemic Plant in the Balearic Islands. Conservation Biology, 19 (2005):421–431.
5. Louis Deharveng. Soil Collembola Diversity, Endemism, and Reforestation: A Case Study in the Pyrenees (France). Conservation Biology, 10 (1996):74–84.
6. K. G. Lyons, C. A. Brigham, B. H. Traut, and M. W. Schwartz. Rare Species and Ecosystem Functioning. Conservation Biology, 19 (2005):1019–1024.
Text © by Chris Maser 2012. All rights reserved.