Biodiversity

or Biological Diversity: An overview

The term ‘Biological diversity’ was used first by wildlife scientist Raymond F. Dasmann in 1968 in the book “A Different Kind of Country”. The term was widely accepted in the 1980s. Thomas Lovejoy (1980), in the foreword to the book, “Conservation Biology” introduced the term to the scientific community for the first time. The term’s contracted form ‘Biodiversity’ was coined by W.G. Rosen (1985) while planning the 1986 National Forum on Biological Diversity organized by the National Research Council (NRC) and the term ‘biodiversity’ was first appeared in a publication in 1988 when sociobiologist E. O. Wilson used it as the title of the proceedings of that forum. Since then, the term has achieved widespread use among biologists, environmentalists, political leaders and common people.

What is biodiversity?

According to the US Office of Technology Assessment (1987), Biodiversity is “the variety and variability among living organisms and the ecological complexes in which they occur”. Probably this was the first definition of the term ‘Biodiversity’. Later on, WWF & other conservation organizations defined it as the variability among living organisms from all sources including inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems.

Origin, Evolution & History of Biodiversity

Biodiversity is the result of 3.5 billion years of evolution. The existing theories on origin of life suggest that life may already have been well-established only a few hundred million years after the formation of the Earth. Until approximately 600 million years ago, all life consisted of archaea, bacteria, protozoans and similar single-celled organisms.

The history of biodiversity during the Phanerozoic (the last 540 million years), starts with rapid growth during the Cambrian explosion (Biodiversity explosion?)—a period during which nearly every phylum of multicellular organisms first appeared. Over the next 400 million years or so, invertebrate diversity showed little overall trend, and vertebrate diversity shows an overall exponential trends. This dramatic rise in diversity was marked by massive losses of diversity classified as mass extinction events. A significant loss occurred when rainforests collapsed in the carboniferous. The worst was the Permian-Triassic extinction event, 251 million years ago. Vertebrates took 30 million years to recover from this event. The fossil record suggests that the last few million years featured the greatest biodiversity in history. Some scientists believe that corrected for sampling artifacts, modern biodiversity may not be much different from biodiversity 300 million years ago., whereas others consider the fossil record reasonably reflective of the diversification of life. Estimates of the present global macroscopic species diversity vary from 2 million to 100 million, with a best estimate of somewhere near 9 million, the vast majority arthropods. Diversity appears to increase continually in the absence of natural selection.

Evolutionary diversification

Most Evolutionary biologists agree that the period since human origin is a part of new mass extinction, named the Holocene extinction event, caused primarily by the impact of humans in the environment. It has been argued that the present rate of extinction is sufficient to eliminate most species on the planet Earth within 100 years. New species are regularly discovered (on average between 5–10,000 new species each year, most of them insects) and many, though discovered, are not yet classified (estimates are that nearly 90% of all arthropods are not yet classified). Most of the terrestrial diversity is found in tropical forests and in general, land has more species than the ocean; some 8.7 million species may exists on Earth, of which some 2.1 million live in the ocean.

Biodiversity is explored at three levels

Biodiversity is usually explored in terms of genes, species and ecosystems at three fundamental hierarchical levels of biological organization. These three diversities are Genetic, Species and Ecosystem diversities. However, Noss (1992, 1996), Szaro & Shapiro (1990) included fourth stage of diversity called Landscape Diversity.

Genetic diversity [diversity within species] refers to the variety of genes within a species, both among geographically separated populations and among individuals within single population. Each species is made up of individuals that have their own particular genetic composition. Within a species there may also be discrete populations with distinctive genes. Therefore, the pool of genetic diversity of a species level can exist at three different levels:-

Genetic diversity within individual (heterozygosity)
Genetic diversity among individuals within a population
Genetic diversity among different populations of a species

To conserve the genetic diversity within a species, different populations must be conserved. This protects the genetic diversity that allows for adaptability to environmental changes and is therefore vital to species survival.

2. Species diversity [diversity between species] refers to the variety of different kinds of species within a region. The factors that determine species diversity are complex and not well understood. Species diversity is not evenly distributed around the world or across continents. 34 biodiversity hotspots have been identified globally. These hotspots collectively comprise just 2.3% of the Earth’s land surface yet hold especially high numbers of species that occur nowhere else – half the world’s plant species and 42% of all terrestrial vertebrate species.

3. Ecosystem diversity [diversity at ecological/habitat level] refers to the variety of ecosystems in a given place. Within any broader landscape there is a mosaic of interconnected ecosystems. It includes variations in the biological communities and the interactions among these levels, so it is often called as Community Diversity.

4. Landscape diversity [diversity at landscape level] refers to variety of a heterogeneous vast land area composed of interacting ecosystems, interspersed with grasslands, meadows, ponds, rivers, lakes, shrubby areas, virgin forests etc. It is also called as Pattern diversity by Scheiner (1992).

Measuring Biodiversity

In spite of many tools and data sources, biodiversity remains difficult to quantify precisely. Actually, to assess the conditions and trends of biodiversity either globally or subglobally, it is necessary to measure the abundance of all organisms over space and time, using taxonomy (such as the number of species), functional traits (for example, the ecological type such as nitrogen-fixing plants like legumes versus non-nitrogen-fixing plants), and the interactions among species that affect their dynamics and function (predation, parasitism, competition, and facilitation such as pollination, for instance, and how strongly such interactions affect ecosystems). Even more important would be to estimate turnover of biodiversity, not just point estimates in space or time. Currently, it is not possible to do this with much accuracy because the data are lacking. There are two long-used measures of biodiversity:-

Species richness (the number of species in a given area) represents a single but important metric that is valuable as the common currency of the diversity of life—but it must be integrated with other metrics to fully capture biodiversity. Richness is a simple measure, so it has been a popular diversity index in ecology, where abundance data are often not available for the datasets of interest.
Ecological indicators are scientific constructs that use quantitative data to measure aspects of biodiversity, ecosystem condition, services, or drivers of change, but no single ecological indicator captures all the dimensions of biodiversity. Ecological indicators form a critical component of monitoring, assessment and decision-making and are designed to communicate information quickly and easily to policy-makers.

Although, Whittaker (1972) described three common metrics used to measure species-level diversity, encompassing attention to species richness or species evenness: Species richness, Simpson index and Shannon-Wiener index. Recently, another new index has been invented called the Mean Species Abundance Index (MSA) which calculates the trend in population size of a cross section of the species. It does this in line with the CBD 2010 indicator for species abundance.
Diversity may be measured at different scales. These are three indices used by ecologists:

The term alpha diversity (α-diversity) was introduced by R. H. Whittaker (1960) together with the terms beta diversity (β-diversity) and gamma diversity (γ-diversity). Whittaker’s idea was that the total species diversity in a landscape (gamma diversity) is determined by two different things, the mean species diversity in sites or habitats at a more local scale (alpha diversity) and the differentiation among those habitats (beta diversity).

Alpha diversity [within-habitat diversity] refers to diversity within a particular area, community or ecosystem, and is measured by counting the number of taxa within the ecosystem (usually species). Alpha diversity (species richness) is used to compare the number of species in different ecosystem types.
Beta diversity [between habitat diversity] refers to the degree to which species composition changes along an environmental gradient (amount of species change or turn over in a particular ecosystem). It is the change in species (usually) diversity between ecosystems and this involves comparing the number of taxa that are unique to each of the ecosystems. High beta diversity implies low similarity between species composition of different habitats. For example, in Ecosystem-A, total number of species is only 100, but individuals of each species are more than 10, while in Ecosystem-B, total number of species is 400, but individuals of each species are 1 or 2 only—so, Ecosystem-A has high beta diversity and Ecosystem-B posseses less beta diversity. It is the reverse in case of alpha diversity—Ecosystem-B possesses high alpha diversity.
Gamma diversity refers to total number of species in a larger geographical area which comprises of several ecosystems—i.e., a measure of the overall diversity for different ecosystems within a region. Therefore, gamma diversity is a kind of alpha diversity only at a larger geographical scale. According to Hunter (2002), “it is geographical-scale species diversity”.

Importance or Scope of Biodiversity

Biodiversity is important in human-managed as well as natural ecosystems. Biodiversity forms the foundation of the vast array of ecosystem services that critically contribute to human well-being:-

Biodiversity is the foundation of ecosystem services to which human well-being is intimately linked.
No feature of Earth is more complex, dynamic, and varied than the layer of living organisms that occupy its surfaces and its seas. This layer of living organisms—the biosphere—through the collective metabolic activities of its innumerable plants, animals, and microbes physically and chemically unites the atmosphere, geosphere, and hydrosphere into one environmental system within which millions of species, including humans, have thrived.
Breathable air, potable water, fertile soils, productive lands, bountiful seas, the equitable climate of Earth’s recent history, and other ecosystem services are manifestations of the workings of life. It follows that large-scale human influences over this biota have tremendous impacts on human well-being.
Biodiversity is important for humans through ecosystem services and goods. Ecosystem services are broken down into regulating services such as air and water purification, provisioning services (goods), such as fuel and food, cultural services and supporting services such as pollination and nutrient cycling

According to Di Castri & Younes (1996), following 6 major Scopes are important to study and save biodiversity, without biodiversity future will blink:-

Biodiversity is the unifying driving force and has the potential to unify all fragmented disciplines of biology and bring together the activities of all scientists professing these disciplines.
Biodiversity is the backbone for agriculture, aquaculture, animal husbandry, Forestry and a host of applied branches in biology.
It has now become highly obligatory for mankind to not only check the alarming global climate change, but also to reconstruct and restore the changed ecosystems to their original state. Such undertakings require a deep understanding of biodiversity in all its aspects.
Biodiversity will offer in the coming decades, new sources of foods, medicines and other essential human needs. For this in-depth knowledge of biodiversity is imperative.
Biodiversity will become the only purposeful scientific tool with which one can bridge the social and cultural world.
Biodiversity is the resource on which all human existence depends—that biodiversity is the pillar of human development.

Constraints or limitations of Biodiversity

Foremost among others, the present dwindling status of taxonomy is the main constraint to grow up biodiversity. Without sound knowledge of taxonomy, members of biodiversity family will not get their proper identity, so recognition and characterization of biodiversity depend critically on taxonomy as it provides the reference system for depicting the pattern of biodiversity.
Measuring biodiversity is the 2^nd major constraint (Hawksworth, 1994) which is closely related to the 1^st point, as without proper documentation & identification by the taxonomy, measurement is not possible.
A dichotomy exists between biodiversity agenda and priorities of developed and developing countries. It is very difficult to resolve this dichotomy at present (K.V. Krishnamurthy, 2003).
The lack of adequate knowledge about biodiversity among the people is another important constraint (K.V. Krishnamurthy, 2003). We should educate people in this respect to resolve this problem.

Global biodiversity

It is the measure of biodiversity on planet Earth and is defined as the total variability of life forms. More than 99 percent of all species, amounting to over five billion species, that ever lived on Earth are estimated to be extinct. Estimates on the number of Earth’s current species range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described. The total amount of DNA base pairs on Earth, as a possible approximation of global biodiversity, is estimated at 5.0 x 10³⁷, and weighs 50 billion tonnes. In comparison, the total mass of the biosphere has been estimated to be as much as 4 TtC (trillion tons of carbon). Another study, published in 2011 by PLoS Biology, estimated there to be 8.7 million ± 1.3 million eukaryotic species on Earth. Global biodiversity is affected by extinction and speciation. The background extinction rate varies among taxa but it is estimated that there is approximately one extinction per million species years. Mammal species, for example, typically persist for 1 million years. Biodiversity has grown and shrunk in earth’s past due to (presumably) abiotic factors such as extinction events caused by geologically rapid changes in climate. Climate change 299 million years ago was one such event. However, the current rate and magnitude of extinctions are much higher than background estimates. This, considered by some to be leading to the sixth mass extinction, is a result of human impacts on the environment.

Global Biodiversity Indices

After the Convention on Biological Diversity was signed in 1992, biological conservation became a priority for the international community. There are several indicators used that describe trends in global biodiversity. However, there is no single indicator for all extant species as not all have been described and measured over time. There are different ways to measure changes in biodiversity. The Living Planet Index (LPI) is a population-based indicator that combines data from individual populations of many vertebrate species to create a single index.The Global LPI for 2012 decreased by 28%. There are also indices that separate temperate and tropical species for marine and terrestrial species. The Red List Index is based on the IUCN Red List of Threatened Species and measures changes in conservation status over time and currently includes taxa that have been completely categorized: mammals, birds, amphibians and corals. The Global Wild Bird Index is another indicator that shows trends in population of wild bird groups on a regional scale from data collected in formal surveys. Challenges to these indices due to data availability are taxonomic gaps and the length of time of each index. The Biodiversity Indicators Partnership was established in 2006 to assist biodiversity indicator development, advancement and to increase the availability of indicators.

Drivers of Biodiversity Change: Natural or human-induced factors that directly or indirectly cause a change in biodiversity are referred to as drivers which are of two types:-

Direct drivers that directly influence ecosystem processes, such as land use change, climate change, invasive species, overexploitation and pollution.
Indirect drivers that indirectly influence ecosystem processes, such as changes in human population, incomes or lifestyle, operate more diffusely, by altering one or more direct drivers.

Four major indirect drivers that influence biodiversity are:

Change in Economic activity: Global economic activity is now nearly seven times what it was 50 years ago and it is expected to grow further. The many processes of globalization have been removing regional barriers, weakening national connections and increasing the interdependence among people and between nations.
Population change: World population has more than doubled in the past forty years, reaching more than 7 billion in 2015. The fact that more and more people live in cities increases the demand for food and energy and thereby pressures on ecosystems.
Socio-Political factors: The trend toward democratic institutions over the past 50 years has enabled new forms of management of environmental resources.
Science and Technology: The development and diffusion of scientific knowledge and technologies can on the one hand allow for increased efficiency in resource use and on the other hand provide the means to increase exploitation of natural resources—causing threat to biodiversity.

Direct drivers that influence biodiversity are:

Habitat fragmentation: Natural disturbances (such as fires) or changes in land use (such as road construction) lead to the fragmentation of habitats of forests. Such habitat changes have a significant impact on biodiversity, as small fragments of habitat can only support small populations that tend to be more vulnerable to extinction.
Invasive alien species that establish and spread outside their normal distribution have been a major cause of extinction to native and endemic taxa. This has particularly affected islands and freshwater habitats and continues to be a problem in many areas, as effective preventive measures are lacking.
Overexploitation remains a serious threat to many species, such as marine fish and invertebrates, forest trees, rare medicinal plants and animals hunted for meat. Most industrial fisheries are either fully or overexploited, while destructive fishing techniques harm estuaries and wetlands. The trade in wild plants and animals and their derivatives is estimated to reach nearly $160 billion annually. Because this trade crosses national borders, the effort to regulate it requires international cooperation to safeguard certain species from overexploitation like Swertia chirayita (Chirata plant), Rauvolfia serpentina (Sarpagandha) etc.
Excessive levels of nutrients in soil: Over the past three decades, excessive levels of nutrients in soil and water have emerged as one of the most important drivers of ecosystem change in terrestrial, freshwater, and coastal ecosystems. More than half of all the synthetic nitrogen fertilizers ever used on Earth have been used since 1985, and phosphorous uses are now three times what they were in 1960.
Climate change: Recent changes in climate, such as warmer temperatures in certain regions, have already had significant impacts on biodiversity and ecosystems. They have affected species distributions, population sizes, and the timing of reproduction or migration events, as well as the frequency of pest and disease outbreaks. Projected changes in climate by 2050 could lead to the extinction of many species living in certain limited geographical regions. By the end of the century, climate change and its impacts may become the main direct driver of overall biodiversity loss.

The Intergovernmental Panel on Climate Change (IPCC) projects that the average surface temperature will rise by 2 to 6.4°C by 2100 compared to pre-industrial levels. This is expected to cause global negative impacts on biodiversity.

According to the projections:

Climate change is likely to exacerbate the loss of biodiversity and increase the risk of extinctions.
Water availability and quality will decrease in many arid and semiarid regions.
The risk of floods and droughts will increase.
The reliability of hydropower and biomass production in some regions will decrease.
Diseases, such as malaria, dengue and cholera, are likely to become more frequent in many regions and so are other health problems linked to heat stress, malnutrition, and natural disasters.
Agricultural productivity may decrease in the tropics and sub-tropics, and fisheries may be adversely affected as well.
Changes in climate, in land use, and in the spread of invasive species will limit both the capability of species to migrate and the ability of species to survive in fragmented habitats.

Distribution

Diversity consistently measures higher in the tropics and in other localized regions such as the Cape Floristic Region and lower in polar regions generally. Rain forests that have had wet climates for a long time, such as Yasuní National Park in Ecuador, have particularly high biodiversity. Terrestrial biodiversity is thought to be up to 25 times greater than ocean biodiversity. A recently discovered method put the total number of species on Earth at 8.7 million, of which 2.1 million were estimated to live in the ocean. However, this estimate seems to under-represent the diversity of microorganisms.

Biodiversity Hotspots

A biodiversity hotspot is a region with a high level of endemic species and simultaneously which are under tremendous threat. The term hotspot was introduced in 1988 by Norman Myers. While hotspots are spread all over the world, the majority are forest areas and most are located in the tropics.

Recently, this ‘hotspot concept’ by Myers has been revised in the light of modern habitat conditions by Mittermeier (2004) in the book “Hotspots Revisited”. A ‘biodiversity hotspot’ must contain at least 1500 spp. of vascular plants as ‘endemics’ (>0.5% of the world’s total) and must have lost at least 70% of its original habitats i.e., it had to have 30% or less of its original vegetation remaining. This book “Hotspots Revisited” recognized 34 global “Biodiversity Hotspots” in 2004 (although Mittermeier et al. again reported 35 in 2011), of these, three of these regions fall in India (Himalayas, Indo-Burma (incl. North-Eastern India) and Western Ghats). Brazil‘s Atlantic Forest is considered one such hotspot (highest among 34), containing roughly 20,000 plant species, 1,350 vertebrates, and millions of insects, about half of which occur nowhere else. Indian Himalayan hotspot contains about 10000 spp. of plants (3160 spp. as endemic), 980 birds and 300 mammals; Indo-Burma hotspot contains 13500 plants (7000 endemic) and western Ghats incl. Sri Lanka include 5000 spp. of plants (1700 endemic).

Hotspot Conservation Initiatives

Only a small percentage of the total land area within biodiversity hotspots is now protected. Several international organizations are working in many ways to conserve biodiversity hotspots.

Critical Ecosystem Partnership Fund (CEPF) is a global program that provides funding and technical assistance to nongovernmental organizations and participation to protect the Earth’s richest regions of plant and animal diversity such as biodiversity hotspots, high-biodiversity wilderness areas and important marine regions.

The World Wide Fund for Nature has derived a system called the “Global 200 Ecoregions“, the aim of which is to select priority Ecoregions for conservation within each of 14 terrestrial, 3 freshwater, and 4 marine habitat types. They are chosen for their species richness, endemism, taxonomic uniqueness, unusual ecological or evolutionary phenomena, and global rarity. All biodiversity hotspots contain at least one Global 200 Ecoregion.

Birdlife International has identified 218 “Endemic Bird Areas” (EBAs) each of which hold two or more bird species found nowhere else. Birdlife International has identified more than 11,000 Important Bird Areas^[5] all over the world.

Plantlife International coordinates several the world aiming to identify Important Plant Areas.

Alliance for Zero Extinction is an initiative of a large number of scientific organizations and conservation groups who co-operate to focus on the most threatened endemic species of the world. They have identified 595 sites, including a large number of Birdlife’ s Important Bird Areas.

The National Geographic Society has prepared a world map of the hotspots and ArcView shapefile and metadata for the Biodiversity Hotspots including details of the individual endangered fauna in each hotspot, which is available from Conservation International.

Causes of depletion of Biodiversity

The most serious aspect of the loss of biodiversity is the extinction of species which is mainly occurred due to the following reasons:-
Population crash/fragmented smaller populations/species with a very narrow geographical range.
Loss of specific pollinators
Loss of reproduction
Low seed germination capabilities
Loss in genetic variation
Species with low population density
Species that need a large home range
Species that migrate
Species with specialized niche requirements
Species that are hunted or harvested by people.
Habitat destruction—mainly due to human impact
Habitat fragmentation—mainly due to human impact
Pollution
Introduction of invasive and exotic species
Diseases due to human activities
Overexploitation due to increasing human population
Shifting or Jhum cultivation by various ethnic groups, mostly in North-Easter Indian States like Nagaland
Sudden natural calamities like floods, El nino, Earthquake etc.

Possible Measures and Biodiversity Conservation

Biodiversity Conservation is one of the paramount concerns throughout the world. Governments, NGOs, Scientists and Social Conservationists are all preoccupied with the problem of devising ways and means of conserving biodiversity. Some effective measures are:-

By ex situ conservation of Threatened wild species:-
Complete organisms are conserved in Botanical Gardens, arboreta, Zoos etc.
Biobanks provide for the conservation of pollen, seeds, sperms, eggs, embryos, somatic cells, tissues etc. by various methods (mostly in liquid nitrogen– -190°C temperature).
Genetic reserves in the form of single-use wild lands can be used to conserve the diversity of selected species.
By in situ conservation:-
Multi-use wild lands to conserve biodiversity in the form of Biosphere Reserve (BR), National Parks (NP), Wildlife Sanctuaries (WLS), Watersheds, Protected Landscapes, Ethnobiological Reserves, Sacred Groves, Game Reserves etc.
Permitting Ecotourism—it has 2 aspects viz., conservation and sustainable management provided to Biodiversity.
Species Survival Commission (SSC—by IUCN)-to support and inspire the SSC Group for conservation.
To support and inspire local people involved in conserving Scared Groves
Apna Van Programme:- Launched by Govt. of India during 1995—This scheme involves afforestation of wasteland, abandoned Jhumlands and degraded Forests by individual or community with subsidy from State Govt @ Rs. 2500/-/hectare for 5 years with a ceiling of 5 hectare for an individual and 20 hectares for village community. This scheme is now very popular in various districts of North-Eastern States of India.
Minimum Need Programme:– This scheme was launched to meet the increasing fuel woods demand of the local people. Here the plantation is raised in abandoned areas in the vicinity of the villages with participation by the villagers. These plantation will meet the fuel requirements of the local people thus relieving pressure on the forests for fuelwoods and helping to improve the ecological balance in these areas.
Joint Forest Management:– like the former, but here villagers are involved to guard the forests instead they will get minor forest products, not involved cutting or felling the trees or root out other species.

AUTHOR

Dr. SUBHASIS PANDA (M.Sc., Ph.D. FIAT, FEHT)
ASSISTANT PROFESSOR OF BOTANY
Angiosperm Taxonomy & Ecology Lab
Under Graduate Deptt. of Botany
Maulana Azad College (University of Calcutta)
Formerly, Barasat & Darjeeling Govt Colleges and Research Fellow,
Botanical Survey of India (1999-2004) , (K.S.Manilal National Awardee in Angiosperm Taxonomy)
Contact: 09433692951. e-mail: bgc.panda@gmail.com; subhaeri@yahoo.com

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