studies for exam Flashcards
positive interactions among species
Atwood and Hammell 2018
Introduction: critical role of marine predators in maintaining essential ecosystem services provided by coastal plant communities (kelp forests, seagrass beds, mangroves, salt marshes). How predator pop changes, due to overharvesting + human activity, triggering trophic cascades = altering the structure of plant communities. Changes in plant communities negatively affect ecosystem services such as coastal protection, carbon sequestration, and overall ecosystem stability. Need for understanding how predator declines affect these services (focus on trophic cascades), the indirect effects predators can have on plant communities through herbivore control.
Method:
Meta-analysis to assess strength/direction of trophic cascades across coastal ecosystems. Involves reviewing a range of studies examining predator impacts on herbivores + plant communities. Focus on salt marshes, mangroves, kelp forests, and seagrass beds, evaluating how predators affect herbivore pops and the vegetation that forms the basis of the ecosystems. Analyse data from diff geographic regions, emphasising ecosystems that are heavily influenced by human activities (overfishing + coastal development).
Findings/Results:
- Marine Predators + Ecosystem Services: predators play a central role in maintaining ecosystem services, a loss of them = trophic cascades, destabilising plant communities and reducing ecosystems services (coastal protection, CO2 sequestration + maintaining biodiversity).
- Coastal Protection: salt marshes * mangroves = buffers against erosion + storm surges. Predator loss = increase in herbivore pops, intensifying grazing pressure on these plants, weakening ability to provide protective services.
- Carbon Sequestration: mangroves, salt marshes, and seagrasses = carbon storage. By controlling herbivore pops, marine predators help maintain plant biomass, supporting carbon sequestration capacity of ecosystems. Without predators, overgrazing reduces plant biomass + carbon storage potential.
- Ecosystem Stability/Resilience: Predators contribute to resilience by controlling herbivore pops + promoting plant diversity. An absence = less stable ecosystems, vulnerable to disturbances + less able to recover.
- Trophic Cascade Variability: In salt marshes, predators have a strong positive effect on plants, moderate effect in mangroves/kelp forests. No effect in seagrass beds. Shows diff ecosystems respond diff to the loss of predators.
- Research Gaps: on trophic cascades in mangroves + seagrass beds (Africa/South America, heavy exploitation).
Conclusion: crucial role of marine predators in sustaining coastal ecosystem services. While research continues to grow, the current understanding is insufficient to conclude predator effects, particularly in mangroves + seagrass. Urgency to conserve predator pops to prevent more degradation, actions should be implemented to prevent further loss of coastal ecosystem functions.
Concept: In salt marshes, fish control the pops of grazing herbivores. Without fish, herbivore pops increase = overgrazing, weakening the plant community, diminishing ecosystem services (coastal protection). Positive feedback loop where predators directly influences the ability of coastal plant communities to maintain ecosystem services.
negative interactions among species
Simberloff & Wilson (1969)
Introduction: Theory of Island Biogeography, explores the factors influencing the no./diversity of species on islands. Diversity of species on an island results from two key processes: immigration + extinction. Island size/distance from mainland influence these processes, and so species richness. Larger islands = more species (greater variety of habitats + resources). Islands closer to the mainland = more species (higher immigration rates). No. of species is in dynamic equilibrium, determined by the balance between the rate of species immigration + rate of species extinction.
Method: theoretical framework (equilibrium model of island biogeography). Principles of island size + distance to predict how species richness changes with these factors. Includes empirical data collected from islands in Florida Keys to support hypothesis.
- Species Immigration: How new species arrive on island.
- Species Extinction: How existing species disappear an island.
- Island Size: Larger islands = lower extinction rates + higher species richness.
- Island Isolation: Islands that are closer to the mainland or other islands tend to receive more immigrant species.
Experimental manipulation on islands in Florida Keys by fumigating islands to remove all species + observing how quickly new species colonise the islands = empirical data to test their theory.
Findings/Results:
- Species-Area Relationship: larger islands = more species + greater variety of habitats, reducing extinction rates (more colonisation) = higher species richness.
- Effect of Island Isolation: Islands farther from mainland have lower immigration rates + fewer species. Difficult to reach.
- Equilibrium Model: islands reach equilibrium where rate of immigration + rate of extinction balance out. When a species is lost, the vacancy is filled by new species. But total no. of species remains relatively constant.
- Experimental Data: In Florida Keys, fumigation = species eradication, the islands showed recolonisation. Islands closer to mainland regained species faster. Species richness over time approached the predicted equilibrium, balance between immigration and extinction.
Conclusion: no. of species on island is determined by balance between immigration + extinction rates. Emphasise that island size + distance from other landmasses are critical factors in determining species richness. Theory has become fundamental to island biogeography, helps explain patterns of species diversity on islands + contributes to our understanding of the dynamics of biodiversity + habitat size and connectivity.
- Factors like species interactions, habitat availability, and disturbance events also influence species dynamics.
Concept: Species-Area Relationship; larger islands support more species because of a greater variety of habitats + resources, reducing extinction rates. Larger areas can support more individuals and have lower extinction rates compared to smaller islands.
protective mutualism
McArthur & Wilson’s (1967)- Equilibrium theory of island biogeography.
Introduction: island biogeography aims to explain the distribution + diversity of species on islands (the no. of species found on an island is determined by a balance between two opposing processes: immigration and extinction). Immigration = arrival of new species from other areas, extinction = loss of species from island due to environmental factors/competition. island size + isolation significantly influence the 2 processes, equilibrium between immigration + extinction determines the no. of species on an island. Applies ecological principles to understand biodiversity patterns on islands + is a foundational work in landscape ecology.
Method: mathematical model considering the factors influencing immigration + extinction rates:
- Island Size: Larger islands = higher no. of species because they offer more diverse habitats/resources + less extinction events due to larger pop sizes.
- Island Isolation: More isolated islands are less likely to receive immigrants = lower species diversity.
Field observations + statistical analysis from various island ecosystems (like Galápagos Islands + islands off the coast of Florida). Mathematical model describes how immigration/extinction rates vary with island size + isolation determining the species equilibrium.
Findings/Results:
- Species-Area Relationship: Larger islands tend to support more species due to larger resources + varied habitats. They also experience fewer extinctions because larger populations of species are more sustainable.
- Isolation and Immigration: More isolated islands have fewer species because they have lower rates of immigration. The isolation leads to reduced chances for species to colonise, especially those requiring specific environmental conditions.
Equilibrium Theory of Biogeography: islands reach an equilibrium no. of species when rates of immigration + extinction are balanced. Varies depending on island size + isolation.
Impact of Distance + Size on Species Diversity: island biogeography is not only a function of the no. of species present but is deeply influenced by the dynamic processes of species turnover + environmental changes.
Conclusion: their theory provides a valuable framework for understanding species diversity patterns on islands.
- Application to Conservation: Theory has implications for conservation; understanding how habitat size + fragmentation affect species richness. Smaller + more isolated habitats may support fewer species + be more vulnerable to extinction.
- Dynamic Equilibrium: island ecosystems are dynamic + constantly evolving, species turnover occurrs as a result of ongoing processes of immigration + extinction.
- Broader Implications: principles of island biogeography can be applied to other fragmented landscapes (nature reserves or patches of habitat in human-dominated landscapes). Insights into how to maintain biodiversity in fragmented ecosystems.
Concept: the no. of species on an island increases with size, seen in the observation of 2 islands: a larger island, more diverse habitats that support more species (greater resources), whilep a smaller island with less diversity in habitats, supports fewer species + has higher extinction rates. Crucial for conservation strategies, conserving larger, more connected habitats is key to maintaining species diversity.
keystone species behaviour + predators
Perino et al. (2020) “Rewilding Complex Ecosystems”
Intro: rewilding = conservation strategy that aims to restore complex ecosystems by reintroducing species and minimising human interference. Ecosystems are dynamic and should evolve naturally + emphasis on reintroducing key species that were once native to the area (apex predators and large herbivores). Argue that rewilding offers a means to restore ecological functions and biodiversity that have been lost due to human activity. + socio-economic aspects = potential challenges/benefits of rewilding (conflicts over land use and public acceptance).
Method: review-based methodology, synthesizing various case studies and rewilding projects from different global regions. Show the successes/challenges of rewilding efforts (reintroduction of wolves in Yellowstone and large herbivores in Europe). Identify knowledge gaps regarding the long-term impacts of rewilding projects. Projects are often evaluated by monitoring changes in biodiversity, ecosystem function, and societal impact.
Findings:
- Positive Ecological Impacts: restore key ecological processes + biodiversity by reintroducing species (apex predators and herbivores). This enhances ecosystem resilience by promoting natural dynamics and reducing human interference.
- Role of Keystone Species: The reintroduction of species (wolves, beavers, and large herbivores (megafauna)) has shown potential in restoring trophic cascades and habitat heterogeneity = greater biodiversity + ecological balance.
- Socio-Economic Benefits + Challenges: provide significant ecosystem services such as carbon storage, flood regulation, and ecotourism opps. Challenges = land-use conflicts, public skepticism, and the high economic costs of rewilding programs remain.
- Knowledge Gaps + context-dependence: need for long-term monitoring to understand success and potential unintended consequences of rewilding. Outcomes can vary based on ecological and social context.
Conclusion:
- Paradigm Shift in Conservation: Rewilding = shift from traditional conservation approaches focusing on maintaining specific ecosystem states, methods embracing dynamic, self-sustaining ecosystems.
- Balancing Nature + People: balancing ecological restoration with societal needs, important to engage stakeholders, addressing conflicts, + educating public about the benefits.
- Adaptive Management: Advocates for adaptive management + ongoing scientific evaluation to optimise rewilding outcomes (biodiversity loss, climate change + ecosystem degradation).
Concept: role of keystone species in ecosystem restoration (wolf reintroduction to National Park = keystone species restoring a trophic cascade). Wolves regulate the elk pop, which allows vegetation (willows/aspens) to recover = helps maintain biodiversity by providing habitat for other species, improving health + resilience of the ecosystem.
