Carrying Capacity

Carrying Capacity & its Impact on Wildlife Population

 In terms of Bailey (1983) “Carrying capacity is the number of animals of a specified quality that a habitat can support while sustaining a specified, but not progressively increasing level of impact on habitat resources.” If management goals do not specify the quality of animals or condition of the habitat then “carrying capacity is simply the number of animals that a habitat can support”.

Essential features of the Carrying capacity concept

1. Carrying capacity is a property of the habitat
2. It is determined by limiting welfare factors. Any combination of welfare factors may be limiting.
3. Carrying Capacity varies as supplies of and animal requirements for limiting factors vary.
4. Carrying capacity is the ability of the habitat to support a number of animals, the quality and productivity of the animals being defined according to management goals.
5. Although habitat condition may be influenced by the number of animals, it is implied that a population at carrying capacity will not cause progressive continuing destruction of the habitat such that management goals cannot be sustained.

The various meanings of carrying capacity

Among various wildlife populations and habitats carrying capacity will be determined by differing sets of limiting factors and can be related to a variety of management goals. No one set of population and habitat conditions will characterize carrying capacity for all types of populations. As such scientists (Dasmann 1964; Caughley 1979; Bailey 1983) find it feasible to distinguish between two types of carrying capacity.

Economic carrying capacity

Economic carrying capacity is defined by management goals for population productivity, animal quality and habitat conditions but is determined by a habitat’s variable and limited ability to sustain achievement of these goals. Economic carrying capacities defined by management goals for population productivity and for population control are termed maximum harvest density and minimum impact density.

Maximum harvest density

The concept is usually applicable to ungulates. It is the number of animals that a habitat will support while producing a maximum sustained harvestable surplus. In terms of the sigmoid model, the population is at or somewhat above the inflection point. The population must be maintained at this level of abundance by harvest. Therefore no lack of welfare factors prohibit the growth of a population

Impact on wildlife populations & its habitat

1. At maximum harvest density, population quality will be very good though not probably the very best possible.
2. Populations at MHD characteristically exhibit a young age structure and high rate of turnover
3. Habitat condition will also be good though not without signs of  use and perhaps retrogressed vegetation 

Minimum impact density

Minimum impact density as a goal for wildlife management aims to reduce the impact of wild animals on those of desirable target species. It may be desirable to maintain a population at MID of carrying capacity if

-         The population is considered to be a pest species, one not to be eliminated but to be controlled

-         The predator population depresses the production of livestock or desirable wildlife species

-         Ungulates compete with valuable and perhaps less competitive wildlife species target of a particular management programme

Impact on wildlife population and its habitat

1. Populations maintained at Minimum impact density of carrying capacity have a very low level of ecological density.
2. Reproduction and resistance to natural mortality is generally high in such populations, requiring persistent and abundant harvest of animals to maintain the population at this level.
3. The population habitat should also be in excellent condition, receiving only minor use from the depressed population.

Ecological carrying capacity

“Ecological carrying capacity is a variable habitat characteristic determined by changeful amounts of welfare factors that limit the size and productivity of a species population.”

Sometimes populations are unharvested, or normal levels of harvest do not influence the population size very much. In these cases carrying capacities are determined only by limiting habitat resources, and it is often useful to distinguish which set of limiting resources is important in determining population size. Ecological carrying capacity as determined by limiting amount of forage or interspersion and of space is termed as subsistence density, security density and tolerance density respectively.

Subsistence density

It is the size of an unharvested population limited primarily by forage. In terms of the sigmoid model subsistence density occurs at the upper asymptote.

Impact on wildlife population and its habitat

1. At subsistence density, population quality and habitat condition will be comparatively poor because this is the ultimate in ecological density.
2. Reproduction is expected to be low and periodic die-off’s will probably occur in years of severe weather.
3. Subsistence density implies that the primary limitation on reproduction and survival is food

Tolerance Density

Tolerance density is the number of animals that a habitat will support when intrinsic behavioral and/or physiological mechanisms are dominant in controlling the population. It is sometimes also called as saturation point density and is especially characteristic of territorial species. In terms of sigmoid model, tolerance density occurs at the upper asymptote. For populations at tolerance density, both spaces as well as intraspecific competition become limiting welfare factors.

Impact on wildlife population and its habitat

1. At tolerance density, all animals may be in good condition or they may be in a hierarchy of condition.
2. The subordinate animals will be in the poorest of condition having low rates of reproduction and survival.
3. Since animals tend to defend resources, there is little or no degradation of limiting factors and therefore the habitat condition is also good.

Security density

Security density as a concept of carrying capacity is the number of animals a habitat will support when welfare factors necessary to alleviate predation are limiting. These welfare factors are escape cover, interspersion and for some animals space. In the sigmoid model security density is at the upper asymptote.

Impact on wildlife population and its habitat

1. At security density, social intolerance may force some animals out of the secure habitat. These animals then suffer high predation losses.
2. Reproduction by dominant animals is high and these animals are in good condition too.
3. Habitat condition should also be good.

Conclusion

Populations in general are found above or below the carrying capacities of their habitats and fluctuate over a continuum of ecological densities. In the long run however, population sizes tend to follow trends in ecological carrying capacities because animal qualities, rates of reproduction and survival and habitat conditions tend to be ecological density dependent. When population is maintained below ecological carrying capacity to maximize harvestable surplus, a precise achievement of this economic goal will depend on understanding the relationship of the population and the habitat to variation in population size and variation in carrying capacity of the habitat. Local data will be needed to achieve this understanding.

Biosphere Reserves : Indian Approach

National Biosphere Reserve Programme

India has created a network of protected areas in the form of 102 National Parks, 515 Wildlife Sanctuaries and 28 Tiger Reserves and 32 Elephant Reserves. The area covered under protected area network accounts for around 5% of the total geographical area of the country. The rich biodiversity in India has given shape to variety of cultural and ethnic diversity which includes over 550 tribal communities of 227 ethnic groups spread over 5,000 forest villages.

The national Biosphere Reserve Programme was initiated in 1986 and its aims and objectives are as follows:

Aims of the Scheme

• To serve as wider base for conservation of entire range of living resources and their ecological foundations in addition to already established protected area network system
• To bring out representative ecosystems under conservation and sustainable use on a long term basis.
• To ensure participation of local inhabitants for effective management and devise means of improving livelihood of the local inhabitants through sustainable use.
• To integrate scientific research with traditional knowledge of conservation, education and training as a part of the overall management of BR.

The Core Advisory Group of Experts, constituted by Indian National MAB Committee identified and prepared a preliminary inventory of 14 potential sites for recognition as BRs in 1979. Subsequently additional BR sites were proposed by the National Committee/State Governments, Experts.

Objectives

It may be noted that BRs are not a substitute or alternative, but a re-enforcement to the existing protected areas. The objectives of the Biosphere Reserve programme, as envisaged by the Core Group of Experts, are as follows:

• To conserve the diversity and integrity of plants and animals within natural ecosystems;
• To safeguard genetic diversity of species on which their continuing evolution depends;
• To provide areas for multi-faceted research and monitoring;
• To provide facilities for education and training; and
• To ensure sustainable use of natural resources through most appropriate technology for improvement of economic well-being of the local people. 
• These objectives should be oriented in such a way that the BRs are the Units wherein the Biological, socio-economic and cultural dimension of conservation are integrated together into a realistic conservation strategy.

What are the Criteria for selection of Biosphere Reserves in India?

The criteria for selection of sites for BRs as laid down by the Core Group of Experts in 1979 are listed below:

Primary criteria

• A site that must contain an effectively protected and minimally disturbed core area of value of nature conservation and should include additional land and water suitable for research and demonstration of sustainable methods of research and management.
• The core area should be typical of a biogeographical unit and large enough to sustain viable populations representing all tropic levels in the ecosystem.

Secondary criteria

• Areas having rare and endangered species
• Areas having diversity of soil and micro-climatic conditions and indigenous varieties of biota.
• Areas potential for preservation of traditional tribal or rural modes of living for harmonious use of environment.

How are Biosphere Reserves designated in India?

At the initiative of the central/state governments, detailed study is carried out and a project report is prepared by the concerned state following the criteria adopted for designation of BRs. The land and forest being the state concerns, the respective state governments have to agree to designate the identified area as Biosphere Reserve. The Central Govt. provides financial assistance for management and research activities in these BRs. The Management of Biosphere Reserves is the responsibility of the concerned State/UT with necessary technical input and training facilities provided by the Central Government.

How Biosphere Reserves are different from protected areas such as National Parks (NP) and Wildlife Sanctuaries(WS)?

Biosphere Reserves in India are not intended to replace existing protected areas but it widens the scope of conventional approach of protection and further strengthens the Protected Area Network. Existing legally protected areas (National Parks, Wildlife Sanctuary, Tiger Reserve and reserve/protected forests) may become part of the BR without any change in their legal status. On the other hand, inclusion of such areas in a BR will enhance their national value. It, however, does not mean that Biosphere Reserves are to be established only around the National Parks and Wildlife Sanctuaries.

However, the Biosphere Reserves differ from protected areas due to their emphasis on :

• Conservation of overall biodiversity and landscape, rather than some specific flagship species, to allow natural and evolutionary processes to continuewithout any hindrance. 
• Different components of BRs like landscapes, habitats, and species and land races. 
• Developmental activities, and resolution/mitigation of conflicts betweendevelopment and conservation,
• Increase in broad-basing of stakeholders, especially local people’sparticipation and their Training, compared to the features of scheme on Wildlife Sanctuaries and National Parks.
• Sustainable environment friendly development, and sustained coordination amongst different development organizations and agencies.
• Research and Monitoring to understand the structure and functioning of ecological system and their mode of reaction when exposed to human intervention.

How many Biosphere reserves are there in India?

According to the Annual report 2010-2011 of Ministry of Environment and Forests, Govt of India, there are at present 17 Biosphere Reserves in the country as shown in the following table: