noc19-bt09 Lecture 05-Species abundance and compostion: Biodiversity
Species Abundance and Composition: Understanding Biodiversity
Introduction to Ecological Structure
- The lecture focuses on species abundance and composition, key components of biodiversity within ecological structures.
- It emphasizes the importance of understanding species distribution and composition in ecosystems.
Observations in Forest Ecosystems
- Forests are highlighted as ideal environments for studying nature due to their minimal human impact, allowing observation of natural processes.
- Different layers of trees (canopies) are described, including top canopies with tall trees, middle canopies, and ground cover consisting of herbs and shrubs.
Species Interactions
- The presence of animals like Chitals is noted; they feed on grasses found in forests.
- An example of a langur-chital association illustrates mutual benefits: langurs provide access to food from trees while alerting chitals to predators.
Population-Level Interactions
- Various animal interactions are observed, such as allogrooming among monkeys which fosters social bonds.
- Migratory birds like Democil Cranes are mentioned as part of the diverse fauna that can be seen in forest ecosystems.
Indirect Signs of Animal Presence
- Pug marks left by tigers serve as indirect evidence of their presence; these imprints help researchers infer animal activity.
- Scat analysis provides insights into animal behavior and population dynamics based on size and scratch marks associated with fecal matter.
Vegetation and Other Organisms
- Observations extend to reptiles like chameleons, pollinators such as bees, and signs like termite mounds indicating a rich ecosystem.
Biodiversity and Its Components
Observations of Biodiversity
- The area may host various fungi, bacteria, reptiles (like muggers), birds, fish, frogs, turtles, and potentially larger animals such as tigers, bears, or elephants.
- These observations highlight the signs of biodiversity present in the ecosystem.
Defining Biodiversity
- Biodiversity is defined as the variety of life in all its forms and at all levels of organization.
- It encompasses different life forms including plants, vertebrates, invertebrates, fungi, bacteria, and microorganisms across various organizational levels.
Levels of Biodiversity
- The three primary levels of biodiversity are genetic diversity, species diversity, and ecosystem diversity.
- Species are defined as groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups.
Understanding Species Diversity
- An example is given with chitals from Kanha and Rajaji; they do not interbreed due to geographical separation but can produce fertile offspring if brought together.
- Reproductive isolation is crucial for defining species; for instance, a chital cannot mate with a tiger.
Genetic Diversity Explained
- Genetic biodiversity examines the variation in genetic information within phyla, families, species populations, and individuals.
- Genes serve as units of heredity passed from parents to offspring; examples include genes determining traits like eye color or height.
Polymorphism in Genetic Diversity
- Polymorphism refers to the proportion of polymorphic genes within a population. A gene is considered polymorphic if its most common allele frequency is below 95%.
Understanding Genetic Polymorphism and Heterozygosity
Genetic Polymorphism
- The concept of polymorphism is introduced, where a gene is considered polymorphic if the frequency of the most common allele is less than 95% in a population.
- An example illustrates allele counts: C1 (200), C2 (100), C3 (150), C4 (1000), and C5 (10,000). The total number of alleles sums to 11,450.
- The frequency calculation for the most common allele (C5) shows it constitutes approximately 87.34%, indicating that this gene is polymorphic since it's below the 95% threshold.
- A hypothetical scenario with an increased count of C5 to 100,000 results in a frequency of about 98.57%, classifying the gene as monomorphic due to exceeding the 95% threshold.
- Definitions clarify that monomorphic genes have only one form, while polymorphic genes exhibit multiple forms based on allele frequencies. A threshold of 95% helps distinguish between these classifications.
Heterozygosity
- Heterozygosity measures genetic diversity by assessing how many genes an average individual has in heterozygous form within a population.
- Using chital as an example, if there are 100 genes and individuals show varying levels of heterozygosity across those genes, averaging these values provides insight into overall genetic diversity.
- The discussion emphasizes that higher heterozygosity indicates greater genetic variability within a population, which can be crucial for adaptability and survival.
Ecosystem Biodiversity
- Ecosystem biodiversity encompasses various ecosystems' types and their distribution within a given area; it examines how many distinct ecosystems exist in a particular environment like forests or wetlands.
- An example contrasts two scenarios: one with only tree ecosystems versus another with diverse ecosystems including grasslands and wetlands, highlighting differences in biodiversity levels based on ecosystem variety.
Understanding Ecosystem Edges and Biodiversity
The Role of Edges in Ecosystems
- Discussion begins on the differences between rocky outcrops and water bodies, focusing on edge types: rocky plus forest and wetland plus forest.
- Introduction of a third edge type: rocky plus wetland. More edges lead to increased biodiversity as different species thrive in these varied habitats.
- Importance of edges is highlighted; certain species prefer living near edges for access to food and safety from predators.
Measuring Biodiversity
Species Richness vs. Species Evenness
- Simplest measure of biodiversity involves assessing species richness (number of species present) and evenness (distribution of individuals among those species).
- Genetic biodiversity is more complex and costly to measure compared to simply counting visible species in an area.
Understanding Species Richness
- Species richness defined as the total number of different species in an area, illustrated with examples comparing two forests with differing numbers of species.
- Explanation of how even if two forests have the same number of species, their biodiversity can differ based on individual distribution.
Exploring Species Evenness
- Example provided where Forest 1 has equal distribution among its 100 species while Forest 2 has one dominant species with a significantly higher population.
- Emphasis on how uneven distribution affects observations; moving through Forest 2 would likely result in seeing only the dominant species.
Assessing Biodiversity Through Accumulation Curves
Concept Introduction
- Introduction to the concept of a species accumulation curve as a method for estimating total biodiversity within a forest ecosystem.
Practical Application
- Description of fieldwork methodology for observing mammals over several days, noting that initial observations yield common animals before rarer ones are spotted later.
Understanding Species Richness and Evenness
Observing Species Over Time
- The observation of species can increase from 11 to 13, indicating the presence of a leopard and an elephant. This highlights how initial observations may yield a high number of species.
- As time progresses, the number of observed species may plateau after initially increasing, suggesting that saturation occurs in biodiversity studies.
- Once saturation is reached, researchers can determine the total number of species present in a given area.
Measuring Biodiversity
- After establishing species richness, the next step is to compute species evenness by noting individual counts for each species during observations.
- For example, if 100 individuals are observed for one species and only 2 for another, this data helps create a stable measure of biodiversity.
Simpson's Diversity Index
- The Simpson's diversity index (D) is calculated using the formula D = 1/sum_i=1^S P_i^2 , where P_i represents the proportion of each species.
- In practical terms, if there are 1000 total individuals across various species, proportions like P_1 = 100/1000 = 0.1 help quantify biodiversity.
Calculating Evenness
- Evenness (E) is derived from dividing D by its maximum value (D max), which occurs when all species have equal representation.
- This concept emphasizes equitability among different species within an ecosystem.
Exploring Different Indices: Shannon Diversity Index
Understanding Shannon's Diversity Index
- The Shannon diversity index is calculated using H = -sum_i=1^S P_i log(P_i) , utilizing natural logarithms to assess biodiversity levels.
Importance of Biodiversity Indices
- These indices provide insights into measuring biodiversity effectively in ecological studies without needing to memorize complex formulas.
Types of Biodiversity: Alpha, Beta, and Gamma
Defining Alpha Biodiversity
- Alpha biodiversity refers to diversity within a specific ecosystem; it assesses how many different species exist within that ecosystem.
Exploring Beta Biodiversity
Understanding Biodiversity: Alpha, Beta, and Gamma Diversity
Defining Biodiversity Levels
- Alpha Diversity: Refers to the diversity within a single ecosystem. It measures the number of species in a specific area. For example, one island may have two species of lizards while another has one species.
- Beta Diversity: Examines the diversity between different ecosystems. It assesses how many unique species exist when comparing two areas. In the previous example, there are three total species across both islands (two on one and one on another).
- Gamma Diversity: Takes biodiversity analysis further by looking at diversity across larger geographical distances, encompassing multiple ecosystems that are far apart from each other.
Practical Example of Biodiversity
- A field situation illustrates alpha and beta diversity using two islands with different habitats (swampy area vs. patch of trees). The first island has three lizard species while the second has only one. This highlights differences in alpha biodiversity between ecosystems.
- If the swamp is drained to create woodland, alpha biodiversity increases as more lizard species can inhabit that area; however, this change impacts beta biodiversity negatively since it reduces overall unique species present across both islands from three to two.
Conservation Efforts Based on Biodiversity Hotspots
- Biodiversity Hotspots: Areas identified for conservation due to their high levels of endemic species (species not found elsewhere) and significant threats such as habitat destruction or disease outbreaks like chytrid fungus affecting frog populations in South America. These hotspots require focused conservation efforts due to their ecological importance and vulnerability.
- The Western Ghats in India serve as an example of a biodiversity hotspot with numerous endemic frog species facing threats from deforestation for agriculture or urban development, necessitating urgent conservation actions to protect these unique ecosystems.
Summary of Key Concepts
- The lecture covered various aspects of biodiversity including definitions and examples of genetic, species, and ecosystem-level diversities.
- Emphasis was placed on understanding how alpha, beta, and gamma diversities interact within ecological structures.
Biodiversity Indices and Hotspots
Understanding Biodiversity Measurement
- The species evenness of an area can be assessed through the species accumulation curve and the number of individuals per species, providing insights into biodiversity.
- To consolidate this information, indices like the Shannon index or Simpson index are utilized to offer a snapshot of biodiversity in terms of species richness and evenness.
Biodiversity Hotspots
- Biodiversity hotspots are regions with high species richness and endemism, meaning many species are unique to these areas.
- The loss of biodiversity hotspots would result in the extinction of unique species that cannot be found elsewhere.