8.1 Ecosystem structure and function disruptions

Toxicants can wreak havoc on ecosystems, messing with food webs and trophic cascades. When predators get hit, it can cause a domino effect, throwing everything out of whack. Even small changes to keystone species can have huge impacts.

Biodiversity takes a hit when toxicants enter the picture. Some species are more sensitive than others, leading to shifts in who's running the show. This can mess with how ecosystems function and make them less stable overall.

Trophic Interactions and Food Webs

Disruption of Trophic Cascades

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• Trophic cascades occur when changes in the population of a predator at the top of the food chain cause ripple effects down to lower trophic levels
• Toxicants can disrupt trophic cascades by reducing predator populations, leading to an overabundance of prey species and potential ecosystem imbalances
• Example: Decline in sea otter populations due to pollution can lead to an increase in sea urchins, which then overgraze kelp forests, altering the entire ecosystem

Impact on Keystone Species

• Keystone species have a disproportionately large influence on the ecosystem relative to their abundance
• Toxicants can significantly impact keystone species, causing widespread changes in the ecosystem
• Loss of keystone species can lead to cascading effects on other species and ecosystem processes
• Example: Bees are keystone species in many ecosystems, and their decline due to pesticides can have far-reaching consequences for pollination and plant diversity

Alterations to Food Web Dynamics

• Food webs represent the complex interactions between species in an ecosystem
• Toxicants can alter food web dynamics by changing species abundances, trophic relationships, and energy flow
• Disruptions to food webs can lead to shifts in community structure and ecosystem functioning
• Example: Pesticides can reduce insect populations, affecting the food supply for insectivorous birds and bats, potentially causing population declines at higher trophic levels

Biomagnification of Toxicants

• Biomagnification is the increasing concentration of a toxicant as it moves up the food chain
• Persistent toxicants (e.g., mercury, PCBs) can accumulate in the tissues of organisms and become more concentrated at higher trophic levels
• Top predators are particularly vulnerable to biomagnification due to their position in the food chain
• Example: DDT biomagnification in the 1960s led to eggshell thinning and population declines in birds of prey like bald eagles and peregrine falcons

Biodiversity and Community Structure

Loss of Biodiversity

• Biodiversity refers to the variety of life at all levels, from genes to ecosystems
• Toxicants can cause biodiversity loss by selectively eliminating sensitive species or altering habitat quality
• Reduced biodiversity can compromise ecosystem stability, resilience, and functioning
• Example: Amphibians are highly sensitive to pollutants, and many species have experienced population declines or extinctions due to toxic exposures

Shifts in Community Composition

• Community composition refers to the relative abundances of different species within an ecosystem
• Toxicants can shift community composition by favoring tolerant species over sensitive ones
• Changes in community composition can alter species interactions, food web dynamics, and ecosystem processes
• Example: Eutrophication caused by nutrient pollution can shift aquatic communities from diverse assemblages to dominance by algae and cyanobacteria

Importance of Functional Redundancy

• Functional redundancy occurs when multiple species perform similar roles in an ecosystem
• High functional redundancy can buffer ecosystems against species loss, as other species can compensate for lost functions
• Toxicants can erode functional redundancy by eliminating species with unique or complementary roles
• Example: In coral reefs, multiple species of herbivorous fish help control algal growth; loss of key herbivores due to pollution can lead to algal overgrowth and reef degradation

Effects on Species Richness and Evenness

• Species richness is the number of different species present in an ecosystem
• Evenness refers to how equally abundant the species are within a community
• Toxicants can reduce species richness by eliminating sensitive species and can alter evenness by favoring certain species over others
• Changes in species richness and evenness can affect ecosystem stability, resilience, and functioning
• Example: Oil spills can cause mass mortality of marine organisms, reducing species richness and altering community evenness in affected areas

Ecosystem Services and Habitat

Disruption of Ecosystem Services

• Ecosystem services are the benefits that humans derive from ecosystems (e.g., clean air, water purification, pollination)
• Toxicants can disrupt ecosystem services by altering ecosystem structure and function
• Loss of ecosystem services can have significant ecological, economic, and social consequences
• Example: Wetlands provide valuable ecosystem services such as water filtration and flood control; pollution can degrade wetland habitats and compromise these services

Habitat Degradation and Loss

• Habitat degradation refers to the deterioration of habitat quality, while habitat loss is the complete destruction of habitats
• Toxicants can contribute to habitat degradation by altering physical and chemical conditions, making habitats less suitable for organisms
• Habitat loss can occur when pollution levels are severe enough to render habitats uninhabitable
• Example: Acid rain caused by sulfur dioxide and nitrogen oxide emissions can degrade forest habitats by acidifying soils and water bodies

Impacts on Nutrient Cycling

• Nutrient cycling refers to the movement and transformation of essential nutrients (e.g., carbon, nitrogen, phosphorus) through ecosystems
• Toxicants can disrupt nutrient cycling by altering microbial communities, soil chemistry, and plant uptake processes
• Disruptions to nutrient cycling can affect ecosystem productivity, decomposition rates, and overall ecosystem functioning
• Example: Heavy metal contamination can inhibit soil microbial activity, slowing down decomposition and nutrient cycling in terrestrial ecosystems

Effects on Primary Productivity

• Primary productivity is the rate at which plants and other autotrophs convert sunlight into biomass
• Toxicants can affect primary productivity by inhibiting photosynthesis, reducing plant growth, or altering species composition
• Changes in primary productivity can have cascading effects on food webs and ecosystem energy flow
• Example: Herbicides can reduce primary productivity in aquatic ecosystems by killing phytoplankton, the base of the aquatic food chain

Implications for Ecosystem Resilience

• Ecosystem resilience is the ability of an ecosystem to withstand and recover from disturbances
• Toxicants can erode ecosystem resilience by reducing biodiversity, altering community structure, and disrupting ecosystem processes
• Ecosystems with low resilience are more vulnerable to collapse or shifts to alternative stable states
• Example: Coral reefs exposed to chronic pollution may have reduced resilience to additional stressors like climate change, increasing the risk of reef degradation and collapse