🪱Parasitology Unit 13 – Parasites: Ecosystem & Environmental Impact

Key Parasites and Their Ecosystems

• Parasites are organisms that live on or within a host organism and obtain nutrients at the host's expense
• Can be found in various ecosystems including terrestrial, aquatic, and marine environments
• Examples of key parasites include:
  • Plasmodium (malaria) in tropical and subtropical regions
  • Toxoplasma gondii (toxoplasmosis) in warm-blooded animals worldwide
  • Trichinella spiralis (trichinosis) in carnivorous mammals
• Parasites often have complex life cycles involving multiple hosts and stages of development
• Host specificity varies among parasites with some being highly specific to a single host species while others have a broad host range
• Parasites play important roles in regulating host populations and shaping community structure within ecosystems
• Can influence ecosystem processes such as nutrient cycling and energy flow through food webs

Parasite Life Cycles and Transmission

• Parasite life cycles involve one or more hosts and can be direct or indirect
• Direct life cycles require only one host species for the parasite to complete its development and reproduction
• Indirect life cycles involve multiple host species with the parasite undergoing development in intermediate hosts before reaching the definitive host
• Transmission of parasites can occur through various routes including:
  • Ingestion of infected hosts or parasite stages (eggs, cysts, larvae)
  • Penetration of skin by infective stages (cercariae of trematodes)
  • Vector-borne transmission (mosquitoes, ticks, flies)
• Parasites have evolved diverse strategies to ensure successful transmission between hosts
  • Production of large numbers of offspring to compensate for high mortality rates
  • Manipulation of host behavior to increase the likelihood of transmission
• Environmental factors such as temperature, humidity, and water availability can influence parasite transmission and survival

Ecological Roles of Parasites

• Parasites play important roles in regulating host populations and maintaining ecosystem stability
• Can act as top-down regulators by reducing host fitness and survival
• Influence host behavior, reproduction, and immune function
• Contribute to the maintenance of genetic diversity within host populations by selecting for resistant individuals
• Mediate interactions between host species and shape community structure
  • Alter competitive relationships between hosts
  • Facilitate coexistence of host species through apparent competition
• Parasites can drive evolutionary arms races with their hosts leading to coevolution and adaptation
• Serve as food sources for other organisms in the ecosystem (hyper-parasites, predators)

Parasites as Ecosystem Engineers

• Parasites can act as ecosystem engineers by modifying the physical and chemical environment
• Alter host morphology, physiology, and behavior in ways that affect ecosystem processes
• Examples of parasite-induced modifications include:
  • Castration of hosts leading to changes in resource allocation and nutrient cycling
  • Manipulation of host behavior to facilitate parasite transmission (increased activity, altered microhabitat use)
• Parasites can create new habitats or modify existing ones
  • Galls induced by parasitic wasps provide shelter and food for other organisms
  • Parasite-induced changes in host morphology can create microhabitats for other species
• Influence ecosystem functioning by altering nutrient cycling, decomposition rates, and primary productivity
• Can have cascading effects on food webs and community structure through their impacts on host populations

Environmental Factors Affecting Parasite Populations

• Temperature plays a critical role in parasite development, survival, and transmission
  • Higher temperatures often accelerate parasite development and increase transmission rates
  • Extreme temperatures can limit parasite survival and distribution
• Humidity and moisture availability are important for the survival and transmission of many parasites
  • Soil moisture influences the survival of parasite eggs and larvae in the environment
  • Aquatic parasites require water for dispersal and host-finding
• Host density and distribution affect parasite transmission and persistence
  • Higher host densities facilitate parasite spread and maintenance of infections
  • Fragmented host populations can limit parasite dispersal and gene flow
• Habitat structure and complexity influence parasite transmission and host-finding ability
  • Vegetation cover can provide microhabitats for parasite survival and transmission
  • Barriers and physical structures can impede parasite movement and host encounter rates
• Anthropogenic factors such as land use change, pollution, and introduction of invasive species can alter parasite populations and transmission dynamics

Impacts on Biodiversity and Food Webs

• Parasites contribute to biodiversity by comprising a significant portion of species richness in ecosystems
• Can drive host diversification through coevolutionary arms races and divergent selection pressures
• Influence the structure and stability of food webs by regulating host populations and mediating trophic interactions
• Parasite-induced host mortality can alter the abundance and distribution of species within communities
• Can create new trophic links and increase food web complexity through their life cycles and transmission routes
• Parasites themselves serve as food sources for other organisms (predators, scavengers) contributing to energy flow in ecosystems
• Loss of parasite diversity can have cascading effects on ecosystem functioning and stability
  • Extinction of host species can lead to the co-extinction of specialist parasites
  • Disruption of parasite-host interactions can alter community dynamics and ecosystem processes

Climate Change and Parasite Distribution

• Climate change is altering the distribution and abundance of parasites and their hosts
• Warming temperatures can expand the geographic range of parasites into previously unsuitable areas
  • Allows parasites to colonize new regions and infect naive host populations
  • Increases the potential for parasite spillover and emergence of new diseases
• Changes in precipitation patterns can affect parasite survival and transmission
  • Droughts can concentrate hosts around limited water sources increasing transmission risk
  • Floods can disperse parasite stages and facilitate their spread to new areas
• Shifts in host phenology and migration patterns due to climate change can disrupt parasite life cycles and transmission dynamics
• Climate-driven changes in habitat suitability and host community composition can alter parasite diversity and prevalence
• Interactions between climate change and other anthropogenic stressors (land use change, pollution) can have synergistic effects on parasite populations and disease risk

Parasites as Bioindicators

• Parasites can serve as bioindicators of ecosystem health and environmental change
• Parasite diversity and abundance can reflect the diversity and stability of host communities
  • Decline in parasite species richness may indicate loss of host diversity or ecosystem degradation
  • Presence of certain parasite species can indicate the health and integrity of specific habitats
• Parasites with complex life cycles involving multiple hosts are sensitive to environmental perturbations
  • Disruption of any stage in the life cycle can lead to the collapse of parasite populations
  • Can provide early warning signals of ecosystem stress or disturbance
• Changes in parasite prevalence or intensity can indicate shifts in host population dynamics or environmental conditions
  • Increase in parasite load may suggest host stress or immunosuppression
  • Decrease in parasite abundance may indicate host population declines or habitat loss
• Monitoring parasite communities can provide insights into the impacts of anthropogenic activities and inform conservation efforts
• Parasites can accumulate contaminants and pollutants from their hosts serving as indicators of environmental contamination
  • Bioaccumulation of heavy metals, pesticides, and other toxins in parasites can reflect exposure levels in the ecosystem
  • Can be used to track the spread and persistence of pollutants through food webs