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From Single Species to Ecosystems—Complementary Approaches

Units of Conservation

Tom Gardali and Nadav Nur, PhD

The successful management of Earth's ecosystems is a mammoth task. Environmental problems are complex and range in size from local to global. Solutions, in order to be successful, require bold steps based on innovative science.

Dysfunctional ecosystems result in the loss of species, of overall biodiversity, and of the goods and services that ecosystems supply. Scientists, using a variety of approaches, must work toward providing creative practical solutions for protecting and restoring healthy ecosystems.
Clockwise from upper left: tidal wetlands; Snowy Plover chick; White-crowned Sparrow; white shark—the spectrum of ‘units of conservation.' PRBO photos · Plover chick by H.& J. Eriksen/VIREO

PRBO's research, sampled in this Observer, illustrates the complementary approaches we take—from studies of species to the understanding of ecosystems—for effective conservation.

Windows to Understanding. Species are our ‘windows' into understanding whole ecosystems. Species interact in complex ways—with each other and with their shared environment. Ecosystems, and hence biodiversity, can only be maintained or enhanced when individual species are maintained or enhanced. To address pressing environmental issues, conservation biologists employ a variety of studies that span the continuum from genes to species to ecosystems. These study approaches are complementary and can best succeed when implemented collectively.

Single-Species Studies. Declines and losses of species worldwide have focused research on reversing declines and halting extinctions. These studies often center on a single imperiled species, like the Bald Eagle or Spotted Owl. From their outset, such single-species studies necessarily looked beyond the species level to understand the ecology of the species, the threats to it and its ecosystem, and the management opportunities that exist to help protect it.

In order to ensure the maintenance or recovery of a threatened species, scientists must first answer the question: What are the critical factors that threaten this species and prevent its recovery? They might examine aspects such as what this species eats (its prey) and what eats it (its predators). In this way, single-species studies end up providing detailed insight into the larger ecosystem. For example, a study of the nesting success of Snowy Plovers at the Point Reyes National Seashore led to a study of space and resource use by the Common Raven (a well known predator of plover nests), as well as to new insights into the harm caused by non-native beach grass to the entire dune ecosystem (see page "Snowy Plovers and Sandy Coastline").

Single-species studies have greatly advanced our knowledge of the causes of species declines, and they have provided the catalyst for innovative research and conservation planning, the basis for species recovery. Effective conservation and management require responding to species-specific needs. That, in turn, depends on insights acquired through intensive studies of species. Single-species work has greatly added to an in-depth understanding of ecosystem functions (and malfunction).

The Warbling Vireo belongs to the suite of birds indicative of Sierra Nevada forest ecosystems. Photo by Tom Grey
Multiple-Species Studies. The need for management and policy decisions to be based on ecosystem-oriented research has increased, due to limited financial resources for conservation coupled with large-scale environmental problems such as climate change. Indeed, comprehensive conservation actions should always be informed by more than the needs of a single imperiled species. However, it is cost-prohibitive to study the entire complement of ecological factors that interact in an ecosystem. One approach is to study multiple species that are sensitive to critical ecological processes (e.g., floods, fire) and/or are associated with key vegetation features (e.g., second-growth conifer forests). PRBO and partners have embraced a focal-species approach in developing bird conservation plans for California's major habitats. The ongoing study of these focal species aims at providing ecosystem-level recommendations for managers (see "Sierran Forest Focal Birds").

Ecosystem Studies. Ecosystem-based management has recently been embraced by resource managers, policy makers, and conservation scientists (see "Ecosystem-based Management"). Ecosystem-focused research aims at benefiting multiple species, as well as maintaining the overall resilience of an ecosystem. Instead of focusing on the ecology of a single species, or even a group of species, this approach emphasizes the study of ecosystem structure, functions, processes, and the factors that affect them (see "Marine Ecosystem Research"). But even here, ecologists have found that the resilience of an ecosystem depends on the interactions among the individual species, representing the range of ecological relationships. Ecosystem-based studies benefit management and policy because they attempt to recognize the relationships among ecological, social, and economic perspectives. Hence, they are often well suited to meet multiple conservation objectives.

Complementary Approaches. No single approach to the study and conservation of species and ecosystems is best: each has its strengths and weaknesses. Implemented in concert, they can be efficient and effective. Single-species studies benefit from broad-scale ecosystem knowledge of a species' prey, predators, competitors, and how those are influenced by still other interacting species; ecosystem-studies benefit from the detailed information garnered from intensive, single-species work. Given the scarcity of financial resources for conservation research, complementary approaches to the study and conservation of biodiversity and ecosystem services are essential.