Taxonomical and Functional Patterns

Taxonomical and Functional Patterns in Invasive Species

Introduction

In this series of lectures, the focus is on understanding the traits that may help predict species invasions. This particular lecture is dedicated to examining taxonomical and functional patterns related to invasive species.

Overview of Invasiveness

  • The discussion will center on whether certain taxons or functional groups show a higher tendency to be invasive than others.

  • Invasive species vary greatly in size and habitat, including small organisms like ctenophores and larger species like nutrias.

  • A significant question arises: do invasive species share common traits?

Taxonomical Patterns in Invasions

Key Studies and Findings

  • Kolar and collaborators conducted a study to examine different traits among plants and birds concerning invasiveness.

  • The analysis focuses on taxonomical patterns rather than solely on organismal traits.

Invertebrates in Coastal Marine Communities

  • According to a review by Ruiz et al., the most prominent groups of invasive species in coastal marine environments in North America are:

    1. Crustaceans

    2. Mollusks

    3. Annelids

    4. Seaweeds

    5. Insects

    6. Cnidarians

    7. Vertebrates

    8. Bryozoans

    9. Protozoans

    10. Sponges

    11. Helminthes

  • In parallel, similar findings are noted in the Mediterranean Sea, where mollusks dominate, followed by arthropods, vertebrates, and seaweeds.

Freshwater Systems Analysis

  • Within freshwater systems, particularly in the Great Lakes, aquatic plants represent the most significant group of invaders, totaling 61 species. The secondary groups include:

    1. Algae

    2. Fish

  • An extensive review by Strayer evaluated introduced animals in freshwater systems, showcasing dominance of vertebrates in the Hudson River basin, followed closely by mollusks.

  • Vertebrates were identified as the most concerning group, followed by crustaceans and mollusks, among the 100 worse invaders globally.

Comprehensive Review of Macroinvertebrate Invasiveness

  • Research by Karatayev et al. investigated 119 species of macroinvertebrate invaders across North America and Europe. The primary invaders were:

    • Crustaceans

    • Gastropods

    • Bivalves (mollusks)

  • Results from this review corroborated Strayer's and Ruiz's findings in coastal communities, revealing predominant taxonomical patterns.

Factors Influencing Invasiveness

Numbers and Diversity

  • Smith and Williams examined global introductions of different algae species, revealing:

    • 165 species of introduced red algae

    • 66 species of introduced brown algae

    • 45 species of green algae

  • The higher number of invasive red algae may relate to their larger overall diversity and specific traits enhancing their introduction success.

Fragmentation and Dispersal Traits

  • Within large families of rhodophytes, such as Ceramiacea and Rhodomelaceae, there are more introduced species than would be predicted by chance. This success is linked to their effective ability to fragment, enhancing dispersal opportunities.

  • A similar exploration in green algae indicated families such as Caulerpaceae and Codiaceae also showed positive deviations from expected values due to their dispersal capabilities and popularity in the aquarium trade.

Ecological Insights into Invasiveness

Composition of Invasive Species

  • A pie chart illustrates that while insects are the predominant group in natural freshwater fauna, they are significantly underrepresented among invasive species in various freshwater systems. Conversely, vertebrates and mollusks are overrepresented, challenging taxonomical distribution norms.

  • Karatayev's work supports this by contrasting proportions of native and invasive species, reiterating the domination of crustaceans and mollusks in the invasive category.

Ecological and Economic Biases

  • The considerable imbalance in the invasiveness of different taxa could stem from biases linked to:

    • Study intensity: Some taxa may receive more attention due to their ecological or economic significance.

    • Variations in introduction pathways: Different vectors for introducing species exhibit distinct selectivities, influencing observed trends.

    • Environmental barriers: Different taxa react variably to environmental challenges, impacting their establishment success. For example, fish may be particularly enhanced by human transport mechanisms due to poor self-dispersal abilities.

Functional Traits of Invasive Species

  • Shifts in ecological traits manifest non-randomly in invasive selections, specifically among functional groups. Notably:

    • In the Hudson River basin, 45% of introduced fish are piscivorous, while only 14% of native fish display this trait.

    • A bias exists among freshwater macroinvertebrates, highlighting a predominance of collector-filterers as invaders, while predators are notably underrepresented.

    • In marine settings (Baltic, Black, Caspian, and North Seas), a similar dominance of filter-feeders exists, comprising approximately 65% of invaders. The flexibility in diet among these organisms (which can utilize microalgae, suspended organic matter, and small zooplankton) possibly aids their success in novel environments.

    • Piscivorous predatory fish may thrive in new habitats due to reduced competition for food resources originally dominated by similar predators.

Conclusion

This examination has highlighted that specific taxa and functional groups exhibit greater invasiveness in both marine and freshwater systems. This phenomenon arises from a combination of biological attributes inherent to the species and biases present in the vectors through which they are introduced. Overall, the lecture underscores a complex interplay between ecological adaptations and human influences on species distribution and success in invasion.