15a. Peay et al. 2013

Introduction

  • Study investigated the impact of rat invasion on fungal communities and wood decomposition.

  • Research locations: islands off the coast of New Zealand, comparing rat-invaded and rat-free islands.

  • Hypothesis: Introduced rats affect fungal community structure and decomposition indirectly through changes in seabird populations and soil environment.

Key Concepts

Indirect Effects of Introduced Species

  • Introduced animals can modify ecosystems through:

    • Trophic cascades

    • Habitat modifications

  • Previous studies focused on plants; less is known about animal effects on decomposer communities.

Functional Redundancy

  • Functional redundancy refers to the presence of multiple species within a community that fulfill similar roles.

  • High redundancy may mean structural changes in communities do not impact ecosystem function significantly.

Experimental Design

Study System

  • Utilized nine rat-invaded and nine uninvaded islands, comparable in size, climate, and geology.

Methodology

  • Used gamma-irradiated branches from Melicytus ramiflorus for consistency and to isolate fungal effects from plant nutrient variance.

  • Branch segments were inoculated with local fungal communities:

    • Inoculation treatments: pooled (mixed from various wood sources), single (one source), or control (no inoculation).

  • Over two years, the experiment measured fungal community structure and decomposition rates of wood.

Results

Fungal Community Structure

Functional redundancy refers to the presence of multiple species within a community that fulfill similar roles. High redundancy may mean structural changes in communities do not impact ecosystem function significantly.

  • Initial fungal composition had variable richness and community assembly across treatments.

  • The study confirmed shallow eventual successions obscured the expected effects of inoculum treatments.

Wood Decomposition Rates

  • Average mass loss of 51.3% from wood branches over two years.

  • Decomposition rates were similar between island types, showing independence from insectivorous activity of rats, yet correlated with initial fungal richness on rat-free islands.

    • On rat-invaded islands, less variability in decomposition rates was observed.

Discussion

Impact of Rat Invasion

  • Rat invasion modified the structure of fungal communities without affecting overall wood decomposition rates.

  • Suggests rats exert indirect effects on fungal community dynamics.

Ecosystem Implications

  • Results indicate that invasion-induced changes in community structure can alter the expected correlations between community composition and ecosystem functions.

  • Functional homogenization is a risk following biological invasions, indicating reduced ecological complexity.

Conclusions

  • Rat invasion alters fungal community composition but not necessarily decomposition outcomes.

  • Remediation or removal of invasive species may reinstate previous ecological relationships between community structure and function.