Biodiversity

BIODIVERSITY

• Biodiversity encompasses the remarkable variety of life forms found on Earth, spanning all levels of biological organization, from genes to ecosystems.
• “Biodiversity”, this term was coined by sociobiologist Edward Wilson, the term highlights the collective diversity across these levels.
• Important components of biodiversity:

Genetic Diversity: Refers to the variety of genes within a species. For instance, the medicinal plant Rauwolfia vomitoria exhibits genetic diversity across different regions, influencing factors like potency and chemical concentration. Examples include India's diverse strains of rice and varieties of mango, each with distinct genetic characteristics.

Species Diversity: Represents the variety of species within a particular habitat or ecosystem. Notably, regions like the Western Ghats boast higher amphibian species diversity compared to other areas like the Eastern Ghats. This diversity is crucial for ecosystem resilience and stability.

Ecological Diversity: Describes the range of ecosystems present in a given region. For example, India's diverse landscape encompasses deserts, rainforests, mangroves, coral reefs, wetlands, estuaries, and alpine meadows, contributing to its high ecological diversity. Contrastingly, countries like Norway exhibit lower ecological diversity due to their different geographical features.

• The accumulation of this rich biodiversity has occurred over millions of years through evolutionary processes.
• However, human activities threaten to erase this wealth in a fraction of that time, with current rates of species loss posing a significant risk.
• Consequently, biodiversity conservation has emerged as a critical global concern.
• Recognizing the vital role of biodiversity in sustaining life and promoting well-being, efforts to conserve and protect it are essential for the continued survival of species, ecosystems, and ultimately, humanity.

Pattern of Biodiversity

• Patterns of biodiversity refer to the non-uniform distribution of species across the Earth's surface and the discernible trends in species richness observed in different geographic regions.
• These patterns provide valuable insights into the factors influencing biodiversity and help scientists understand the underlying mechanisms driving species distributions and diversity gradients.
• Two prominent patterns of biodiversity are latitudinal gradients and species-area relationships.

Latitudinal gradients

• Latitudinal gradients refer to the phenomenon where the diversity of plants and animals varies along a latitudinal axis, from the equator to the poles.
• Biodiversity is not evenly spread across the globe but exhibits patterns, with one of the most notable being the latitudinal gradient in diversity.
• Tropical Dominance: Generally, species diversity decreases from the equator towards the poles. The tropics, spanning from 23.5° N to 23.5° S latitudes, host more species compared to temperate or polar regions.
• Examples: Colombia near the equator boasts around 1,400 bird species, while New York at 41° N has 105 species, and Greenland at 71° N has only 56 species. India, largely in tropical latitudes, harbors over 1,200 bird species.
• Richness in the Tropics: Tropical regions like the Amazon rainforest exhibit unparalleled biodiversity, housing thousands of plant, animal, and insect species. For instance, the Amazon contains over 40,000 plant species, 3,000 fish species, and numerous other taxa.
• Special Characteristics of the Tropics:

- Long Evolutionary Time: Tropical latitudes have remained relatively undisturbed for millions of years, providing ample time for species diversification through evolution.

- Less Seasonality: Unlike temperate regions, tropical environments experience less seasonal variation, which promotes niche specialization and leads to greater species diversity.

- More Solar Energy: The tropics receive more solar energy, which fuels higher productivity and indirectly contributes to greater biodiversity by supporting diverse ecosystems and food webs.

Species-area Relationships

• During explorations in South American jungles, Alexander von Humboldt noticed that as the explored area increased within a region, species richness also increased, but only up to a certain limit.
• Rectangular Hyperbola Relationship: The relationship between species richness (S) and area (A) is often depicted as a rectangular hyperbola. When plotted on a logarithmic scale, this relationship forms a straight line described by the equation: log S = log C + Z log A.

• Important parameters:

- Slope (Z): The slope of the line in the species-area relationship equation. Ecologists have found that the value of Z typically falls within the range of 0.1 to 0.2, regardless of the taxonomic group or region.

- Y-Intercept (C): Represents the value of species richness when the area is zero.

• Consistent Slopes: Despite variations in taxa and regions, the slopes of the regression lines are remarkably similar. For example, whether studying plants in Britain, birds in California, or molluscs in New York state, the slopes remain consistent.
• Steeper Slopes for Larger Areas: When analyzing species-area relationships on a continental scale or larger, such as entire continents, the slope of the line becomes steeper, with values ranging from 0.6 to 1.2.
• Interpretation of Steeper Slopes: In this context, steeper slopes indicate that as the area increases, species richness rises more rapidly. For instance, frugivorous birds and mammals in tropical forests exhibit a slope of 1.15, suggesting that larger tropical forests support disproportionately higher numbers of species compared to smaller areas.
• Overall, species-area relationships provide valuable insights into the distribution and richness of species within ecosystems and highlight the importance of habitat size in supporting biodiversity.

Importance of species diversity to the ecosystem

• Stability and Productivity: Ecologists have long debated whether the number of species in a community affects ecosystem functioning. One measure of a stable community is its ability to maintain consistent productivity over time and resist disturbances. Research by David Tilman using outdoor plots suggests that communities with higher species richness exhibit less year-to-year variation in biomass and tend to be more productive.
• Ecosystem Health: Although the precise mechanisms linking species richness to ecosystem health are not fully understood, it is widely acknowledged that rich biodiversity is crucial for ecosystem well-being. Ecosystems with diverse species are better equipped to perform essential functions like nutrient cycling, pollination, and pest control.
• Human Survival: Rich biodiversity is not only essential for ecosystem health but also imperative for the survival of the human race. As species face extinction at alarming rates, it raises questions about the significance of losing individual species. While there are no direct answers to such questions, an analogy proposed by ecologist Paul Ehrlich, known as the 'rivet popper hypothesis,' offers perspective.
• Rivet Popper Hypothesis: Ehrlich's analogy likens species in an ecosystem to rivets in an airplane. Each species plays a vital role in supporting ecosystem functions, much like rivets hold an airplane together. While removing a few rivets may not immediately affect flight safety, continued loss weakens the plane over time. Similarly, as species become extinct, ecosystem resilience and functionality are compromised, posing long-term risks to human well-being.
• Every species in an ecosystem contributes to its overall functioning, and the loss of even a single species can have cascading effects. Preserving biodiversity is essential for maintaining ecosystem stability, resilience, and the services they provide, ultimately safeguarding the well-being of both ecosystems and humanity.

Loss of Biodiversity

• Human Impact: Human activities are driving the rapid decline of biodiversity worldwide. Colonization of tropical Pacific Islands by humans alone has led to the extinction of over 2,000 species of native birds. The International Union for Conservation of Nature (IUCN) Red List documents the extinction of 784 species in the last 500 years, including vertebrates, invertebrates, and plants.
• Examples of Extinctions: Notable examples of recent extinctions include the dodo, quagga, thylacine, Steller's Sea Cow, and three subspecies of tigers. In the past two decades alone, 27 species have disappeared.
• Vulnerability Across Taxa: Extinctions are not random; certain groups like amphibians are more susceptible. Currently, over 15,500 species worldwide are facing the threat of extinction, including 12% of all bird species, 23% of all mammal species, 32% of all amphibian species, and 31% of all gymnosperm species.
• Comparison with Pre-Human Extinctions: While mass extinctions have occurred throughout Earth's history, the current "Sixth Extinction" differs in its rate. Extinction rates today are estimated to be 100 to 1,000 times faster than in pre-human times, with human activities driving the accelerated pace.
• Potential Consequences: Loss of biodiversity can have far-reaching consequences, including:

- Decline in Plant Production: Reduced biodiversity may lead to decreased plant productivity, impacting food sources and ecosystem stability.

- Lowered Resistance to Environmental Perturbations: Ecosystems with reduced biodiversity are less resilient to environmental stressors such as drought, leading to increased vulnerability.

- Increased Variability in Ecosystem Processes: Loss of species diversity can disrupt important ecosystem processes like water use, nutrient cycling, and pest and disease regulation, leading to unpredictable fluctuations and imbalances.

• Overall, the loss of biodiversity poses significant risks to ecosystem health, stability, and the well-being of both natural ecosystems and human societies. Urgent conservation efforts are needed to mitigate further loss and preserve Earth's rich biological heritage for future generations.

Cause of Biodiversity Loss

• The accelerated rates of species extinctions are primarily attributed to human activities, with four major causes often referred to as 'The Evil Quartet: Habitat Loss and fragmentation, climate change, overexploitation and invasive species.
• These four factors, collectively known as 'The Evil Quartet,' represent the primary drivers of biodiversity losses worldwide.
• Addressing these threats requires concerted efforts at local, national, and global levels to promote sustainable land use, mitigate climate change, regulate resource exploitation, and manage invasive species effectively.
• Protecting biodiversity is essential not only for the conservation of species and ecosystems but also for maintaining the health and resilience of our planet's natural systems.

Habitat Loss and Fragmentation

• Habitat loss and fragmentation are the leading causes pushing animals and plants towards extinction. Among the most severely affected ecosystems are tropical rainforests, which have experienced a dramatic reduction in their extent over time. Once covering over 14% of the Earth's land surface, these vital ecosystems now occupy less than 6%.
• Tropical rainforests are disappearing at an alarming rate, with significant portions being cleared for agricultural purposes such as soybean cultivation or conversion into grasslands for cattle ranching. The Amazon rainforest, known as the "lungs of the planet" due to its role in oxygen production, is particularly vulnerable to deforestation.
• Tropical rainforests are home to millions of species, and their destruction poses a grave threat to global biodiversity. When these habitats are lost, countless plant and animal species lose their homes, leading to population declines and, in some cases, extinction.
• In addition to outright destruction, many habitats are also degraded by pollution, further endangering species survival. Pollution from various sources can harm ecosystems and disrupt ecological processes, making habitats unsuitable for certain species.
• Habitat fragmentation occurs when large habitats are divided into smaller, isolated fragments due to human activities like urbanization and infrastructure development. This fragmentation poses challenges for species that require large territories or have migratory habits, as it restricts their movement and access to resources. This can lead to population declines and increased vulnerability to extinction.

Overexploitation

• Throughout history, humans have relied on nature for sustenance and shelter. However, when this reliance transitions from necessity to excessive consumption driven by greed, it results in over-exploitation of natural resources.
• Over-exploitation occurs when resources are harvested or utilized at a rate that exceeds their natural ability to replenish. This can occur due to unsustainable hunting, fishing, logging, or other extraction activities driven by human demand.
• Many species extinctions over the past 500 years, such as the Steller's sea cow and the passenger pigeon, have been attributed to over-exploitation by humans. These species were hunted to extinction for their valuable resources without consideration for their population sustainability.
• Presently, many marine fish populations worldwide are over-harvested due to commercial fishing practices. Overfishing leads to the depletion of fish stocks, endangering the continued existence of some commercially important species and disrupting marine ecosystems.
• Over-exploitation not only threatens the survival of targeted species but also disrupts ecosystems and reduces biodiversity. It can lead to cascading effects, such as loss of habitat and food sources for other species, and destabilize ecosystems, impacting their ability to provide valuable ecosystem services.
• To mitigate the impacts of over-exploitation, sustainable management practices are essential. This includes setting limits on harvesting rates, implementing regulations to prevent overfishing or overhunting, and promoting responsible consumption habits to ensure the long-term viability of natural resources.

Alien Species Invasions

• Alien species, also known as non-native or introduced species, are organisms that are introduced unintentionally or deliberately to new environments, often for purposes such as agriculture, aquaculture, or landscaping.
• Some alien species become invasive when they establish populations and spread rapidly in their new habitats, outcompeting native species for resources and disrupting ecosystems. Invasive species pose a significant threat to biodiversity and can lead to the decline or extinction of indigenous species.
• One notable example is the introduction of the Nile perch into Lake Victoria, which resulted in the extinction of over 200 species of cichlid fish, a unique ecological assemblage in the lake. Similarly, invasive weed species like carrot grass (Parthenium), Lantana, and water hyacinth (Eicchornia) have caused significant environmental damage and threatened native species in many regions.
• The recent illegal introduction of the African catfish Clarias gariepinus for aquaculture purposes poses a threat to indigenous catfish species in rivers. Competition for resources and predation by invasive species can disrupt native ecosystems and reduce populations of native plants and animals.
• Invasive species can alter habitat structure, nutrient cycling, and food webs, leading to cascading effects on ecosystem functioning and biodiversity. They can also increase the risk of disease transmission and have economic implications for agriculture, forestry, and fisheries.
• Efforts to prevent the introduction and spread of invasive species include monitoring and surveillance, implementing regulations on trade and transportation, and controlling populations through eradication, containment, or biological control methods.

Coextinctions

• Co-extinction refers to the phenomenon where the extinction of one species leads to the extinction of other species that are associated with it in an obligatory manner. This can occur in various ecological relationships, such as mutualisms, parasitism, or predator-prey interactions.
• When a species becomes extinct, the plant and animal species that depend on it for survival or reproduction also face extinction. For example, when a host fish species becomes extinct, its unique assemblage of parasites, which rely on the fish for their life cycle, also becomes extinct.
• Co-extinctions can also occur in mutualistic relationships, such as plant-pollinator interactions. In cases of coevolved mutualisms, where species have evolved together and depend on each other for survival, the extinction of one species inevitably leads to the extinction of the other.
• Co-extinctions can have significant ecological consequences, disrupting ecosystem dynamics and reducing biodiversity. They can lead to the loss of important ecological functions, such as pollination, seed dispersal, or nutrient cycling, and destabilize ecosystems.
• Co-extinctions can trigger cascading effects, where the loss of one species sets off a chain reaction of extinctions across multiple trophic levels. This can further exacerbate biodiversity loss and ecosystem degradation.
• Recognizing the potential for co-extinctions highlights the interconnectedness of species within ecosystems and underscores the importance of conservation efforts to protect not only individual species but also the ecological relationships they participate in. By preserving biodiversity and ecosystem integrity, we can mitigate the risk of co-extinctions and maintain the stability and resilience of natural systems.