Community Characteristics PDF

Community Characteristics Community Definition: A community is characterized by species richness (number of species) and species evenness (relative abundance of species). Dominant Species: Communities are often named after their dominant plant species, as these species signific...

Community Characteristics Community Definition: A community is characterized by species richness (number of species) and species evenness (relative abundance of species). Dominant Species: Communities are often named after their dominant plant species, as these species significantly influence the community structure. Ecological Disturbances Definition: An ecological disturbance is any event that disrupts the ecological status quo, affecting biotic or abiotic factors. Types of Disturbances: These can be periodic (e.g., hurricanes) or random (e.g., meteorite impacts), and can also be anthropogenic (human-induced). Succession Ecological Succession: This is the process by which communities develop over time, which can be primary (on new land) or secondary (on previously disturbed land). ○ Primary Succession: Occurs on newly formed land (e.g., after a landslide), starting with pioneer species like grasses and mosses. ○ Secondary Succession: Follows disturbances in existing communities (e.g., abandoned pastures or after a fire), beginning with species from the seed bank. Pioneer and Climax Communities Pioneer Species: These are the first species to colonize disturbed areas, often short-lived and adapted to harsh conditions. Climax Community: A stable community that develops after succession, but can be disrupted by disturbances. Ecosystem Changes During Succession Changes in productivity, plant biomass, nutrient distribution, and species diversity occur throughout the stages of succession, with early stages typically having high productivity and low diversity, while late stages show the opposite. Intermediate Disturbance Hypothesis This hypothesis suggests that moderate levels of disturbance can enhance species diversity, while too little or too much disturbance can reduce it. Adaptations to Disturbance 1. Many species in California's wildlands are adapted to periodic wildfires, with some requiring fire to germinate. Post-fire, annual species known as "fire followers" emerge from the seed bank, while certain perennials survive by resprouting. Species Interactions: ○ Competition: Interspecific competition occurs between different species, while intraspecific competition occurs within a species. Tansley’s experiments demonstrated that species can coexist depending on environmental conditions and competition for resources. ○ Ecological Niche: Refers to the role and space a species occupies, including its resource use and interactions with other species. 2. Competitive Exclusion Principle: States that two species cannot coexist if they compete for the exact same resources. However, species can coexist by utilizing slightly different resources through niche partitioning. 3. Types of Trophic Interactions: ○ Predation: Involves a predator consuming prey, leading to the prey's death. ○ Parasitism: A parasite consumes parts of a living host without immediately killing it. ○ Herbivory: Herbivores consume plants, which can be complete or partial. ○ Detritivory: Detritivores feed on dead organic material without directly affecting living populations. 4. Adaptations: ○ Predator Adaptations: Include size, weaponry (teeth, claws, venom), and sensory adaptations to locate prey. ○ Prey Adaptations: Include camouflage, escape strategies, and chemical defenses (e.g., aposematic coloration and mimicry). 5. Symbiosis: Refers to long-term interactions between species, which can be: ○ Commensalism: One species benefits while the other is unaffected. ○ Mutualism: Both species benefit, which can be trophic (resource exchange), defensive (protection), or dispersive (pollination). ○ Parasitism: One species benefits at the expense of the other. 6. Mutualism and Coevolution: Mutualistic relationships can lead to coevolution, where interacting species evolve in response to each other. The document discusses the diversity problem in ecology, highlighting historical discrimination against minority communities that affects their access to nature, and how this contributes to the underrepresentation of diverse groups in the field. Additionally, it emphasizes the importance of integrating Western scientific methods with Indigenous Traditional Ecological Knowledge (TEK) to create a more inclusive understanding of ecology. The lecture further explores community diversity in terms of species richness and evenness, while acknowledging the challenges of measuring biodiversity due to socio-economic factors and changing ecosystems. Key Points Historical discrimination has created barriers for minority communities in ecology, resulting in a lack of diversity in the field. Socioeconomic factors impact access to wilderness, contributing to disparities in ecological engagement and career paths. The concept of belonging and role models influences the participation of diverse groups in ecology. Western science, rooted in a specific cultural tradition, may conflict with non-Western worldviews, necessitating a more inclusive approach. Traditional Ecological Knowledge (TEK) from Indigenous cultures can provide valuable insights that complement Western scientific methodologies. Measuring community diversity involves assessing both species richness and species evenness, though complete documentation of species is often impractical. Environmental factors and community changes over time pose challenges for studying biodiversity, as communities are dynamic and continuously evolving. What is Ecology? Definition: Ecology is defined as the study of the complex interrelationships among organisms and their environment, a concept first articulated by Ernst Haeckel in the 19th century. Importance: Understanding ecology is crucial due to pressing ecological issues like habitat destruction and the need for sustainable practices. It also satisfies human curiosity about the natural world. Levels of Ecological Hierarchy The ecological hierarchy consists of several levels, each addressing different questions: 1. Organism: Focuses on individual species and their interactions with the environment. 2. Population: Examines groups of the same species living together. 3. Community: Studies interactions among different species in a shared environment. 4. Ecosystem: Looks at the interactions between organisms and their physical environment (both biotic and abiotic). 5. Landscape: Involves multiple ecosystems at a regional scale. 6. Biosphere: Encompasses all ecosystems and living organisms on Earth. Energy in Ecosystems Source of Energy: The sun is the primary energy source for most ecosystems, with exceptions like deep-sea hydrothermal vents where chemoautotrophs thrive.  Trophic Levels: Organisms are categorized into trophic levels: ○ Primary Producers: Autotrophs (e.g., plants) that capture solar energy. ○ Primary Consumers: Herbivores that consume plants. ○ Secondary and Tertiary Consumers: Carnivores that eat herbivores and other carnivores, respectively. ○ Detritivores: Organisms that feed on dead organic matter. Trophic Interactions These interactions form a complex web, known as a food web, which illustrates the relationships and energy flow between different organisms. Distinctions Between Related Fields Ecology vs. Environmental Science vs. Environmentalism: ○ Ecology: Focuses on biological interactions and ecosystems. ○ Environmental Science: Integrates ecology with abiotic factors and often includes expertise from other fields (e.g., chemistry, policy). ○ Environmentalism: A political advocacy movement aimed at protecting the environment, distinct from the scientific study of ecology. Historical Context The document traces the evolution of ecological study from naturalism, which emphasized observation and description of nature, to modern ecology, which incorporates quantitative research and experimentation. Figures like John Muir exemplify the naturalist tradition, combining exploration, observation, and advocacy for conservation. Conclusion The document emphasizes that ecology is not only vital for understanding the natural world but also for addressing environmental challenges. It encourages a blend of scientific inquiry and advocacy to foster a deeper appreciation and protection of ecosystems. Summary of the Article: "Trophic Cascades at Multiple Spatial Scales Shape Recovery of Young Aspen in Yellowstone" Hypothesis The article looks at how the reintroduction of gray wolves in Yellowstone National Park has affected elk behavior and numbers, which in turn impacts the recovery of young aspen trees due to less eating. The scientists believe that both how many elk there are (density-mediated) and how elk behave (behaviorally mediated) play a role in the recovery of aspen by lowering the amount of browsing (eating) on them. Introduction In the past, young aspen trees in Yellowstone were heavily eaten by elk, especially when there were no wolves around in the early 1900s. When wolves were brought back to the park in the mid-1990s, the elk population started to decrease, and their behavior changed, leading to a potential recovery of aspen trees. This study aims to look at how elk numbers and their eating habits affect aspen growth in different areas of Yellowstone. Main Results 1. Large Spatial Scale: ○ Elk numbers dropped significantly from 1999 to 2015, which correlated with taller young aspen trees as their browsing decreased. Aspen started to grow well when elk numbers fell below about 4 elk per square kilometer. ○ The ratio of wolves to elk increased after wolves were reintroduced, showing that wolves strongly influenced elk populations. 2. Medium Spatial Scale: ○ Comparing two areas (Glen Creek and Mammoth), the study found big differences in aspen recovery. In Glen Creek, where wolves were more active, young aspen averaged 207 cm tall and had been browsed 64% of the time. At Mammoth, where wolves were less present due to humans, young aspen averaged only 31 cm tall and had been browsed 89% of the time. ○ This suggests that human activity protected elk from predation, allowing them to eat many aspen trees and prevent their growth. 3. Small Spatial Scale: ○ In areas with certain risks from predators (like places where escape was hard), less eating was seen, and young aspen grew taller in Glen Creek. However, no such effects were found in Mammoth, where elk continued to browse heavily regardless of these risk factors. Conclusions The study concludes that bringing back wolves has greatly influenced elk numbers and their eating habits, resulting in a noticeable recovery of young aspen trees in Yellowstone. The findings support the idea that both the number of elk and their behavior are important for aspen recovery. As the amount of browsing has decreased, aspen trees are starting to grow back, suggesting a positive change in the plant community that could help restore aspen and other tree species in the ecosystem. The authors highlight the need to understand these interactions for better wildlife management and conservation efforts in similar areas.