WASC 302 Exam review
Invasive Species
Geographic Barriers to Dispersal
Examples: Oceans, mountains, deserts, large lakes.
Barriers vary by species (e.g., mountains block plants but not birds).
Wallace's six global biodiversity realms: Nearctic, Ethiopian, Palearctic, Oriental, Australasian, Neotropical.
Definitions and Impacts of Invasive Species
Invasive species: Introduced outside their native range, often harmful. Most likely to cause a threat to economic, ecological, and human health
Major vectors: planes (didn’t exist before the 20th century), ships and humans
Exotic species: From another region, may not pose threats.
Introduced species: Deliberate or accidental introduction, impact neutral.
Alien species: Introduced to a specific ecosystem. -> All similar
Classical Model of Invasion
Natural Colonization:
What allows invaders to invade?
Broad environmental tolerance:
Traits for colonizing wide habitats.
Local adaptation:
Rapid adaptation to local conditions.
Ecological and Economic Concerns
Threats to native biodiversity, ecosystems, human health, and economies.
Accelerated by human activities (e.g., shipping, travel).
Ballast Water in Ships
Ships loaded with cargo are stable and do not need ballast water because they are drafted down in the water
Ships without cargo carry ballast water to increase stability (they bob in the water with no cargo)
Single biggest source of invasive species globally
Case Study: Great Lakes Invasions
Major invasion vector: Ships (75% of non-indigenous species post-1959).
Examples:
Zebra mussels, spiny waterflea: Introduced via ballast water.
Asian carp: Poised to enter; threaten food webs by competing for plankton.
Invasion hotspots: Huron-Erie corridor, despite most discharges in Lake Superior.
How can we determine where invasive species originated?
Track the vector: look at import: export records
Look at pathways that airlines & ships utilize
Assess at genetic composition of the populations in introduced areas and source areas
Tracking and Mitigation
Origin determination methods:
Analyze trade routes and genetic profiles.
Strategies:
Improve ballast water management.
Monitor and control overland transport vectors (e.g., fishing equipment, bilge water).
Vulnerabilities and Responses
Climate and habitat suitability in the Great Lakes for invasive species.
Actions needed: Policy enforcement, public awareness, habitat restoration.
Climate Change
Key Impacts on Lakes
Physical Changes:
Increased water temperature.
Reduced ice duration. -> melting earlier
Altered precipitation patterns. -> droughts
Changes in groundwater levels.
Enhanced evaporation rates. -> more salinity
Sedimentation dynamics.
Stable mixing/stratification patterns.
Chemical Changes:
Shifts in nutrient and dissolved organic carbon (DOC) levels. -> affects algae growth
Movement and dynamics of contaminants.
Biological Changes:
Altered demographic parameters and ecosystem productivity. -> birth and death rates
Range limits -> species change
Community composition. -> allow species to live in areas they could not before
Changes in phenology (timing of events in a lake)
Observed Trends
Global lake warming at 0.34°C per decade, faster than air (0.25°C) or ocean surface (0.12°C) temperatures.
Significant decline in ice coverage and more stable lake stratification.
Arctic Lakes and Permafrost Thaw
Changes in zooplankton communities (e.g., increased macroinvertebrates).
Shifts in community composition due to permafrost thaw slumps. -> calcium levels increase
Influence of Evaporation and Precipitation
Long-term salinity changes in northern Great Plains lakes.
High salinity lakes: Dominated by Harpacticoid copepods and Artemia.
Low salinity lakes: Contain species like Daphnia spp., Ceriodaphnia, and calanoid copepods.
Zooplankton Responses to Climate Change
Evolutionary potential due to large populations and short generation times.
Examples:
Daphnia pulex can evolve tolerance to slightly increased salinity (0.1-1‰) in 5-10 generations.
Daphnia magna has a higher salinity tolerance compared to Daphnia longispina.
Salinity Tolerance and Drought Studies
Salinity limits for reproduction observed in Daphnia magna (~5.9‰).
Past extreme droughts show resilience in species like Ceriodaphnia, suggesting potential survival of future climate-induced droughts.
Hatching vs. Salinity
Positive cross correlation: as salinity is higher, so is hatching index
Methodologies
Resurrection Ecology: Testing zooplankton from historical sediments to assess evolutionary changes.
Toxicity Tests: Evaluating threshold limits for salinity tolerance.
Conclusion
Evidence indicates zooplankton species can adapt to salinity changes and droughts, though future climate scenarios may present unprecedented challenges.
Projected droughts will last longer and be more extreme than any testes in our study (still a question on how population will do during climate change)
Zooplankton Ecology
Grazing in Aquatic Systems
Grazing: Predator-prey interactions involving algae and bacteria as prey.
Filtering is an example of grazing in the aquatic world; removal of algae or the portion of water volume that is (ideally) cleaned of particles
Key zooplankton grazers:
Cladocerans (Daphnia ambigua, Bosmina longirostris).
Copepods: Herbivorous calanoids and predatory cyclopoids.
Rotifers (Keratella, Kellicottia).
Grazing mechanisms:
Filter-feeders: Nonselective (except for size of food), small prey (e.g., cladocerans, some rotifers).
Raptorial: Medium-sized particles chosen based on chemical qualities (e.g., copepods).
Feeding and Growth
Particle size for filter feeders:
Lower limit: 0.16–4.2 µm for cladocerans.
Upper limit: 20–50 µm for copepods.
Growth factors:
Influenced by food quality, food quantity, and temperature.
Higher food and warmer temperatures increase growth rates.
Zooplankton – Factors Affecting Growth
Population growth rate (r): N(t) = N(0) where r is the growth rate of the population in units of 1/time
Filtration rate = volume of water cleared of particles per unit time, mL or % per unit time
Growth rate often seems to be limited by food and temperature (both quantity and quality of food are important) r = birth rate – death rate
Filtering rates are a function of temperature and body size
Patterns of Abundance and Activity
Synchrony: Zooplankton populations in temperate/polar regions often grow in synchronized patterns.
Most common in copepods which require sexual reproduction
Cladocerans and rotifers, there is less synchrony due to asexual reproduction
Predation Impact:
Leptodora predation linked to high death rates in Daphnia populations.
Fish predation leads to diel vertical migration (zooplankton avoid surface during the day).
Zooplankton may hide in macrophyte beds during the day to avoid fish predation and migrate at night.
Top-down vs. Bottom-up Control:
Top-down: Predators (e.g., fish) regulate zooplankton types and sizes.
Bottom-up: Phosphorus levels drive zooplankton biomass via phytoplankton growth.
Fish and Zooplankton Interactions
Feeding:
Fish shift diets based on prey density and size
If prey are large and scarce, fish consume them one at a time
If prey are small and abundant, fish will filter water column – Mechanical Sieving
Size-selective predation: Larger zooplankton are targeted for higher energy return.
Case Study: Crystal Lake, Connecticut:
Introduction of alewives caused a shift from large to small zooplankton.
Supports the Size Efficiency Hypothesis:
Larger zooplankton dominate in absence of predators due to better filtering efficiency.
Predation pressure reduces large forms, allowing smaller forms to thrive.
Larger forms come to dominate
If fish size-selective predation is intense, larger forms are selected to be eaten, allowing smaller forms to dominate
If predation pressure is moderate, large forms are reduced, and this allows coexistence of forms
Conclusions
Zooplankton dynamics are shaped by interactions with predators, food availability, and environmental conditions.
Both top-down and bottom-up forces contribute to ecosystem structure and function.