Focal species : A multi-species umbrella for nature conservation

To prevent the further loss of species from landscapes used for productive enterprises such as agriculture, forestry, and grazing, it is necessary to determine the composition, quantity, and configuration of landscape elements required to meet the needs of the species present. I present a multi-species approach for defining the attributes required to meet the needs of the biota in a landscape and the management regimes that should be applied. The approach builds on the concept of umbrella species, whose requirements are believed to encapsulate the needs of other species. It identifies a suite of “focal species,” each of which is used to define different spatial and compositional attributes that must be present in a landscape and their appropriate management regimes. All species considered at risk are grouped according to the processes that threaten their persistence. These threats may include habitat loss, habitat fragmentation, weed invasion, and fire. Within each group, the species most sensitive to the threat is used to define the minimum acceptable level at which that threat can occur. For example, the area requirements of the species most limited by the availability of particular habitats will define the minimum suitable area of those habitat types; the requirements of the most dispersal-limited species will define the attributes of connecting vegetation; species reliant on critical resources will define essential compositional attributes; and species whose populations are limited by processes such as fire, predation, or weed invasion will define the levels at which these processes must be managed. For each relevant landscape parameter, the species with the most demanding requirements for that parameter is used to define its minimum acceptable value. Because the most demanding species are selected, a landscape designed and managed to meet their needs will encompass the requirements of all other species. Especies Focales: Una Sombrilla Multiespecífica para Conservar la Naturaleza Resumen: Para evitar mayores pérdidas de especies en paisajes utilizados para actividades productivas como la agricultura, la ganadería y el pastoreo, es necesario determinar la composición, cantidad y configuración de elementos del paisaje que se requieren para satisfacer las necesidades de las especies presentes. Propongo un enfoque multiespecífico para definir los atributos requeridos para satisfacer las necesidades de la biota en un paisaje y los regímenes de manejo que deben ser aplicados. El enfoque se basa en el concepto de las especies sombrilla, de las que se piensa que sus requerimientos engloban a las necesidades de otras especies. El concepto identifica una serie de “especies focales”, cada una de las cuales se utiliza para definir distintos atributos espaciales y de composición que deben estar presentes en un paisaje, así como sus requerimientos adecuados de manejo. Todas las especies consideradas en riesgo se agrupan de acuerdo con los procesos que amenazan su persistencia. Estas amenazas pueden incluir pérdida de hábitat, fragmentación de hábitat, invasión de hierbas y fuego. Dentro de cada grupo, se utiliza a la especie más sensible a la amenaza para definir el nivel mínimo aceptable en que la amenaza ocurre. Por ejemplo, los requerimientos espaciales de especies limitadas por la disponibilidad de hábitats particulares definirán el área mínima adecuada de esos tipos de hábitat; los requerimientos de la especie más limitada en su dispersión definirán los atributos de la vegetación conectante, las especies dependientes de recursos críticos definirán los atributos de composición esenciales; y especies cuyas poblaciones están limitadas por procesos como el fuego, la depredación o invasión de hierbas definirán los niveles en que deberán manejarse estos procesos. Para cada parámetro relevante del Paper submitted September 19, 1996; revised manuscript accepted February 24, 1997. 850 Focal Species for Nature Conservation Lambeck Conservation Biology Volume 11, No. 4, August 1997 Introduction Throughout the world, changing patterns of land use have resulted in the loss of natural habitat and the increasing fragmentation of that which remains. Not only have these changes altered habitat composition and configuration, but they have modified the rates and intensities of many ecological processes essential for ecosystems to retain their integrity. As a consequence, many landscapes that are being used for productive purposes such as agriculture, grazing, and forestry, are suffering species declines and losses (Saunders 1989; Saunders et al. 1991; Hobbs et al. 1993). Attempts to prevent further loss of biological diversity from such landscapes requires a capacity to define the spatial, compositional, and functional attributes that must be present if the needs of the plants and animals are to be met. There has been considerable debate in the ecological literature about whether the requirements of single species should serve as the basis for defining conservation requirements or whether the analysis of landscape pattern and process should underpin conservation planning (Franklin 1993; Hansen et al. 1993; Orians 1993; Franklin 1994; Hobbs 1994; Tracy & Brussard 1994). Speciesbased approaches have taken the form of either singlespecies studies, often targeted at rare or vulnerable species, or the study of groups of species considered to represent components of biodiversity (Soulé & Wilcox 1980; Simberloff 1988; Wilson & Peter 1988; Pimm & Gilpin 1989; Brussard 1991; Kohm 1991). Species-based approaches have been criticized on the grounds that they do not provide whole-landscape solutions to conservation problems, that they cannot be conducted at a rate sufficient to deal with the urgency of the threats, and that they consume a disproportionate amount of conservation funding (Franklin 1993; Hobbs 1994; Walker 1995). Consequently, critics of single-species studies are calling for approaches that consider higher levels of organization such as ecosystems and landscapes (Noss 1983; Noss & Harris 1986; Noss 1987; Gosselink et al . 1990; Dyer & Holland 1991; Salwasser 1991; Franklin 1993; Hobbs 1994). These alternative approaches place a greater emphasis on the relationship between landscape pattern and processes and community measures such as species diversity or species richness (Janzen 1983; Newmark 1985; Saunders et al . 1991; Anglestam 1992; Hobbs 1993, 1994). Although approaches that consider pattern and processes at a landscape scale help to identify the elements that need to be present in a landscape, they are unable to define the appropriate quantity and distribution of those elements. Such approaches have tended, by and large, to be descriptive. They can identify relationships between landscape patterns and measures such as species richness, but they are unable to define the composition, configuration, and quantity of landscape features required for a landscape to retain its biota. Ultimately, questions such as what type of pattern is required in a landscape, or at what rate a given process should proceed, cannot be answered without reference to the needs of the species in that landscape. Therefore, we cannot ignore the requirements of species if we wish to define the characteristics of a landscape that will ensure their retention. The challenge then is to find an efficient means of meeting the needs of all species without studying each one individually. In order to overcome this dilemma, proponents of single-species studies have developed the concept of umbrella species (Murphy & Wilcox 1986; Noss 1990; Cutler 1991; Ryti 1992; Hanley 1993; Launer & Murphy 1994; Williams & Gaston 1994). These are species whose requirements for persistence are believed to encapsulate those of an array of additional species. The attractiveness of umbrella species to land managers is obvious. If it is indeed possible to manage a whole community or ecosystem by focusing on the needs of one or a few species, then the seemingly intractable problem of considering the needs of all species is resolved. Species as diverse as Spotted Owls (Franklin 1994), desert tortoises (Tracy & Brussard 1994), black-tailed deer (Hanley 1993) and butterflies (Launer & Murphy 1994) have been proposed to serve an umbrella function for the ecosystems in which they occur. But given that the majority of species within an ecosystem have widely differing habitat requirements, it seems unlikely that any single species could serve as an umbrella for all others. As Franklin (1994) points out, landscapes designed and managed around the needs of single species may fail to capture other critical elements of the ecosystems in which they occur. It would therefore appear that if the concept of umbrella species is to be useful, it will be necessary to search for multi-species approaches that identify a set of species whose spatial, compositional, and functional requirements encompass those of all other species in the region. I present a method for selecting, from the total pool of species in a landscape, a subset of “focal species” whose paisaje, se utiliza a la especies con los mayores requerimientos para ese parámetro para definir su valor aceptable mínimo. Debido a que se seleccionan las especies más demandantes, un paisaje diseñado y manejado para satisfacer sus necesidades abarcará los requerimientos de todas las demás especies.