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FACTORS THAT INFLUENCE THE “CARRYING CAPACITY” OF GAME SPECIES
V. Gulca1, P. Angelstam2, R.H. Barrett3
1
National Academy of Science of Belarus, Centre for Bioresources, Minsk, Republic of Belarus, [email protected]
2Swedish University of Agricultural Sciences, School for Forest Management, Skinnskatteberg, Sweden, [email protected]
University of California, Department of Environment Science, Policy and Management, Berkeley, CA, USA, [email protected]
Introduction
The term carrying capacity was coined by Aldo Leopold (1933:50-51) in his work “Game management”, and is one of the most common concepts in wildlife management (Caughley & Sinclair 1994). However, the interpretation of this concept and its application in practical management varies. For example, while Morrison 2000:46 argued that ”... while carrying capacity may be equated with a certain level of habitat quality, the quality itself should be based not on the number of organisms but on the demographics of individual populations.” From other parts of the world scholars have argued that the “concept of carrying capacity is the cornerstone for sustainable game management, because it brings clarity to many questions in the theory and practice of wildlife management’’ (Юр-генсон 1969 quoted by Львов 1984). Although, according to Almasan (1988), rankings of carrying capacity for hunting land management units were elaborated only in former socialist countries, the term covers a variety of meanings, and unless we a careful and define the term, we may merely cause confusion (Caughley & Sinclair 1994, Львов 1984).
For example, apart from density or demographics of the focal game species of interest to hunters, estimates of carrying capacity also depend on the consequences of a particular game species composition and density for other aspects of ecosystems. For example, large herbivore populations causing acceptable damage to less preferred tree species (e.g., Scots pine) of importance to boreal forestry may still cause severe damage to more preferred tree species (e.g., aspen) of importance for forest biodiversity conservation (Angelstam et al. 2000). It is thus possible to identify management contexts professional wildlife management and conservation (public land in the US), opposing stakeholder views and unresolved conflict (Sweden) and with evident crisis in wildlife management and conservation (Moldova).
Un-reflected consideration to carrying capacity issues is not a guarantee
to succeed in wildlife and habitat conservation. First, we list reasons why it is important to estimate carrying capacity. Second, we identify what factors influence carrying capacity and how it is perceived among stakeholders. Finally, we discuss the need to include both target species, the ecosystem in which it lives and different stakeholders views to define different levels of carrying capacity.
Why it is important to estimate carrying capacity
According to Caughley & Sinclair (1994) ecological carrying capacity is the natural limit of a population set by resources in a particular environment. This equals the mean maximum number or biomass of organisms of a given species that can be sustained or survive on a long-term basis within an ecosystem (Helms, 1998). According to Negrutiu (1983) the term that expresses the conditions offered by given hunting land management unit for one hunting species is called carrying capacity. However, using large herbivores as an example, other stakeholders may focus on the state of its predators, the herbivores' food species or other effects of herbivores as vectors of disease. What carrying capacity is varies thus among stakeholders with different focus.
To evaluate feasible management options for different stakeholders, including to solve management problems such as reducing the impact of increased browsing by wild herbivores; increasing wildlife populations quality; increasing number of wildlife individuals; anticipating conflicts; identifying, controlling and removing limiting factors; balancing of agricultural, forestry, and wildlife management interests; renting of hunting grounds; accurate estimates a systems analysis approach is needed. Given this complexity, while carrying capacity remains an important topic, it is ambiguous, and all relevant variables are rarely taken into account in management and modeling of populations, ecosystems and landscapes (Morris & Mukherjee 2007, Angelstam et al. 2000).
What factors influence carrying capacity?
A principle developed in agricultural science by Carl Sprengel (1828) and later popularized by Justus von Liebig, states that population growth is controlled not by the total amount of resources available, but by the scarcest resource (the limiting factor). Shelford's Law of Tolerance holds that first the presence and then the success of an organism depend on the completeness of a complex of conditions. More precisely, each organism - whether the individual or the species population - is subject to an ecological minimum, maximum, and optimum for any specific environmental factor or complex of factors linked to a particular aspect of the coupled human and nature system, or landscape.
Discussion
Because the concept of carrying capacity is relative to particular elements of landscapes and how they are used, and not stipulated in any law, both ecological and social systems need to be studied. Research about carrying capacity thus encompasses a wide range of questions. What are different stakeholders' views on the balance between game populations and other parts of ecosystems? What is the effect on population density, demography, health and trophy quality of different views on carrying capacity? What is the power of different stakeholders?
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