BIOL240 Week 2 Lecture notes

Biodiversity in Aquatic Systems

• Introduction mentions various organisms found in aquatic systems.

• Some specific species highlighted include:

  • Whirligig beetles

  • Water striders

  • Mosquito larvae and pupae

  • Boatmen

  • Scorpions

  • Diving beetles

Freshwater Communities

• Greater species richness in freshwater than marine habitats.

• This species abundance is questioned with "Why?"

Freshwater Diversification

• Adaptation of organisms to diverse environments promotes organismal diversity.

  • Source: National Academy of Sciences

Taxonomic Diversification

• Taxa without tissues

  • Radial symmetry

    • Growth through increase in body mass.

    • Locomotion via ciliary movements and trochophore larvae.

• Key groups discussed include:

  • Lophotrochozoa: grow by molting; coelom formed from embryonic gut.

  • Ecdysozoa

  • Parazoa

  • Radiata

  • Protostomes

  • Deuterostomes

• Notable taxa: Sponges, Cnidarians, Ctenophorans, Lophophorates, Flatworms, Mollusks, Annelids, Nematodes, Arthropods.

• Example of Arthropoda includes Mollusca and Crustaceans.

Phylum Mollusca

• Dominant groups: Bivalvia and Gastropoda.

• Approx. 4,000 known freshwater gastropod species.

• Freshwater adaptations arose independently in multiple lineages:

  • Neritimorphs, Caenogastropods, Pulmonates.

• Specific adaptations of pulmonate snails and their ecological roles:

  • Bivalves serve as filter feeders.

Phylum Arthropoda – Subphylum Crustacea

• Major groups include:

  • Class Branchiopoda: Order Cladocera (water fleas) & Anostraca (fairy shrimp).

  • Class Copepoda

  • Class Ostracoda: Seed shrimp.

  • Class Malacostraca: Includes shrimps, yabbies, and crabs.

• Biodiversity includes various trophic roles.

Phylum Arthropoda – Subphylum Chelicerata

• Dominated by mites and some spiders (Class Arachnida).

• Approximately 5,000 species predominated by mites.

• Most mites are ectoparasites; their lifecycle is often linked to host organisms.

Phylum Arthropoda – Subphylum Hexapoda (Insects)

• First terrestrial insects appeared in the Devonian (410-354 mya).

• Aquatic insects like Mayflies date back to the Carboniferous (354-298 mya).

• High freshwater insect diversity with an emphasis on:

  • Orders: Odonata, Coleoptera, Ephemeroptera, Hemiptera, Diptera.

• Many insects do not spend their entire life in freshwater.

Aquatic Insect Biodiversity

• Most common orders are:

  • Diptera (Flies)

  • Coleoptera (Beetles)

  • Hemiptera (Water striders)

• Orders that are exclusively aquatic include:

  • Odonata (Dragonflies/Damselflies)

  • Ephemeroptera (Mayflies)

  • Trichoptera (Caddisflies)

• Life history transitions commonly involve aquatic juvenile stages.

Characteristics of Insects

• Phylum Arthropoda, subphylum Hexapoda:

• Related to crustaceans and chelicerates. Features include:

  • Three pairs of legs

  • Body segmented into three parts

  • Pair of antennae

  • Chitinous exoskeleton

  • Open circulatory system

  • Breathing adaptations, utilizing spiracles and tracheal tubes for respiration, especially under water.

Insect Life Histories

• Two main life cycles:

  • Holometabolism: Egg - Larvae - Pupae - Adult (complete metamorphosis).

  • Hemimetabolism: Egg - Nymphs - Adult (without pupal stage).

• Common characteristics include egg-laying, and life stages often exhibit different ecological roles.

Drivers of Aquatic Insect Biodiversity

• Spatial variability in species diversity (latitudinal patterns).

• Environmental factors regulating diversity include:

  • Stream speed

  • Duration of water availability

  • Oxygen levels

  • Sedimentation rates

  • Nutrient availability

Adaptations of Insects to Aquatic Environments

• Evolution from terrestrial forms facilitating various strategies:

  • Diffusion: Common in small insects and larvae.

  • Gills: Present in immature stages for oxygen extraction.

  • Oxygen storage techniques, such as trapped air bubbles or plastron mechanisms for submerged species.

  • Siphons: Breathing adaptations mimicking snorkels to access atmospheric oxygen.

Summary of Breathing Adaptations

• Key aquatic respiration strategies:

  • Atmospheric oxygen utilization

  • Diffusion across integument

  • Temporary air bubbles and plastron mechanisms

  • Siphon adaptations for accessing surface oxygen.

Strategies for Locomotion Under Water

• Diver strategies:

  • Natatorial legs for swimming; streamlined body forms.

• Strider strategies:

  • Ability to walk on the surface tension of water, primarily seen in Hemiptera.

Coping with Ephemeral Water Availability

• Adaptations include:

  • Dual habitat living (aquatic and terrestrial).

  • Dispersal mechanisms utilizing migratory waterbirds.

  • Diapause as a strategy for survival during adverse conditions.

Strategies for Dealing with Water Flow

• Techniques to maintain position in flowing waters:

  • Building protective casings from debris (caddisfly larvae).

  • Flattened body forms to minimize resistance in currents.

Insects as Bioindicators

• Insects serve as indicators of stream health, sensitive to:

  • Organic content

  • Oxygen levels

  • Algal abundance

• Changes in insect populations reflect ecological shifts in freshwater systems.

Characteristics of Freshwater Habitats

• Definition: Freshwater, with salinity under 5 ppt.

• Comprises less than 2% of Earth's water.

• Types of freshwater included:

  • Streams, pools, lakes, aquifers, ephemeral ponds.

• Greater variability compared to marine environments in terms of physical and chemical characteristics.

Freshwater Ecology Basics

• Ecosystem features:

  • Energy capture by primary producers.

  • Chemical energy transfer among organisms.

  • Energy loss as heat.

  • Matter recycling in ecosystems.

Freshwater Trophic Ecology

• Two main energy pathways in freshwater ecosystems:

  • Heterotrophic (detritus-based pathways).

  • Autotrophic (producer-based pathways).

River Continuum Concept

• Relates species distribution to the physical attributes of freshwater bodies.

• Functional feeding groups identify the roles of organisms in organic matter cycling.

Human Impacts on Freshwater Ecosystems

• Major threats include:

  • Eutrophication

  • Altered hydrology

  • Invasive species

  • Sedimentation and chemical residues

Eutrophication Explained

• Nutrient enrichment leading to phytoplankton blooms.

• Causes light penetration issues, affecting submerged plants and ecosystem health.

Altered Hydrology

• Issues like groundwater extraction and interrupted flows can dramatically alter ecosystems.

  • Case study: Murray Darling Basin's fish kill events linked to these hydrological changes.

Summary of Human Impacts

• Human activities severely threaten the biodiversity and health of freshwater ecosystems.

• Conservation efforts will be crucial to restore and protect these vital habitats.