Biotic Resistance to Invasive Species

Overview of Biotic Resistance to Invasive Species

This document captures the key concepts and details discussed in the provided lecture about biotic resistance in relation to invasive species. Emphasis is placed on the mechanisms through which native species might limit the success of non-native invaders, contextualized within various ecosystems and experimental findings.

Introduction to Biotic Resistance

Invasive species can thrive in new environments; however, success varies among different recipient communities. The key determinant of this variance lies in biotic resistance from native species, which can impede the establishment or spread of non-native species. The notions explored include:

  • Propagule pressure: Referring to the number of individuals introduced to a new environment, impacting invasive success.
  • Ecological Factors: Focus on recipient community-based attributes affecting non-native success.

The Biotic Resistance Hypothesis

The biotic resistance hypothesis states that native species can hinder the establishment of non-native species through two main interaction types:

  • Competitive Interactions: Involves competition for resources (light, nutrients) among different species.
  • Consumptive Interactions: Involves predation, herbivory, or parasitism, where native species directly consume or negatively impact non-natives.

Competitive Interactions

  1. Example of Zostera japonica:

    • Study by Bando: Investigating competition between the invasive Japanese eelgrass (Zostera japonica) and the native eelgrass (Zostera marina), it was found that Z. japonica achieved higher biomass when grown alone compared to mixed conditions, indicating competitive pressure.
    • Mechanisms: Potential competitive mechanisms included competition for light and nutrients, and chemical effects (allelopathy). Z. marina provided partial resistance by reducing Z. japonica's growth without completely outcompeting it.

  2. Example of Sargassum muticum:

    • Study by Britton-Simmons: Examined the establishment of the invasive brown alga (Sargassum muticum) against native algae. Turf algae were shown to inhibit S. muticum recruitment. When various types of algae were removed, successful recruitment of S. muticum was only noted in the absence of all competing algae, illustrating that turf algae and canopy algae played distinct roles in biotic resistance.

  3. Study by Dethier and Hacker:

    • Investigated Spartina anglica in different marsh types (low and high salinity). Although competitive interactions from neighboring native species typically did not hinder the establishment of Spartina, there were instances in high-salinity marshes where native plants provided some resistance by restricting establishment to areas with fewer competitors.

Consumptive Interactions

  1. Pathogen Interactions:

    • Study by Mitchell and Power: Found that native pathogens in a species’ natural habitat affect its invasive potential. Newly introduced plants in new regions had a lower pathogen load. The data indicated that invasive plants accumulating pathogens had reduced invasiveness compared to those that did not.

  2. Predation by Native Species:

    • Blue Crab and Zebra Mussels: Research by Carslsson et al. showed predation by native blue crabs significantly impacted zebra mussel populations in the Hudson River, demonstrating the role of native predators in mitigating invasions.
    • Herbivore Interactions: Parker and Hay studied the feeding preferences of native crayfish on invasive freshwater plants, concluding that generalist herbivores tended to prefer eating invasive biomass over native, suggesting a potential for biotic resistance through herbivory.
    • Synergistic Effects: In a study by Harvey et al., the presence of native predator fish was shown to negatively impact the abundance of an invasive fish species, implying that multiple predator species working in tandem can produce greater effects on introduced species than individually.

  3. Predation Pressure on Sea-Squirts:

    • Focused on the survival of invasive tunicates, showing that predation pressure altered invasion success depending on tidal height, with stronger resistance at lower tidal heights.

Biogeographical Factors and Physical Habitat Variations

Biotic resistance is influenced by broader biogeographical factors:

  • Tropical vs. Temperate Systems: Research suggests that tropical marine systems generally feature higher herbivory (e.g., from herbivorous fish), thus likely enhancing resistance to algal invasions compared to temperate systems where herbivory is lower.
  • Habitat Types: Varied habitats exhibit different capacities for resisting invasions. For example:
    • Hard substrates (such as rocky shores) show stronger resistance compared to soft sediments, where foundation species like seagrasses and oysters do not effectively resist invasions.

Experimental Studies

Research conducted by Dr. Cebrian and others examined reserve effects of herbivores (like sea urchins) on two invasive macroalgae (Lophocladia lallemandii and Caulerpa racemosa). The findings indicate:

  • Uptake of native algae likely contributes to the decline in invasive algae due to indirect competition through grazing.
  • Herbivory showed effectiveness in controlling the abundance of incipient populations of algae while having lesser effects on established invasions.

Meta-Analysis of Biotic Resistance

Recent reviews (Kimbro et al.) highlighted general patterns across various studies regarding biotic resistance:

  • Evidence of biotic resistance exists, with stronger effects observed when both competitions (competitive and consumptive interactions) are at play.
  • There is a noted gradient of resistance based on latitude, with tropical regions demonstrating increased efficacy in native resistance compared to temperate locales.
  • Environmental and habitat shifts influence the strength and capacity of biotic resistance considerably, implying a complex interplay of interactions in marine ecosystems.

Conclusion

The lecture concludes that biotic resistance from native species can play essential roles through both competition and consumption, with varying strength based on environmental contexts, habitat types, stages of invasion, and geographical factors. This research underlines the nuanced and context-dependent nature of biotic resistance, with critical implications for managing invasive species and conserving native biodiversity.