Biogeography & Marine Realms Lecture Notes
Geographic Distribution of Fossils
Fossil Evidence from Different Continents:
South America: Fossil evidence of the Triassic therapsid Lystrosaurus.
Africa: Fossil remains of Cynognathus, a Triassic therapsid approximately 3 m long.
India: Fossil remains of the freshwater reptile Mesosaurus.
Australia: Fossils indicative of ancient flora and fauna.
Antarctica: Fossils of the fern Glossopteris, found in all of the southern continents, indicating they were once joined.
Dr. C. Nicolai Roterman - Background
Position: Deep-sea Ecologist at the University of Portsmouth.
Research Focus:
Evolution and biogeography.
Population dynamics and connectivity.
Speciation and resilience.
Utilization of molecular tools, including study of hydrothermal vents and Yeti crabs.
Learning Objectives
By the end of these sessions, you should be able to:
Describe and define biogeography.
Discuss key concepts and the importance of biogeography.
Understand why species live in specific environments.
Key Concepts Covered
Biogeography.
Species distributions.
Barriers to dispersal.
Vicariance.
Species invasions.
Definition of Biogeography
Biogeography explores:
The distribution of species.
How groups of species form distinct ecosystems and their geographical limits.
Major theme: Identifying and characterizing geographical groupings of species and the biogeochemical conditions differentiating them.
Questions addressed:
Why are there different animals in different places?
Integration of concepts from ecology, evolutionary biology, genetics, geology, and physical geography/oceanography.
Historical and Ecological Explanations
Historical Explanations: Focuses on past distributions and geological or climatic events.
Evidence includes fossil distributions and tectonic records.
Ecological Explanations: Looks at present distributions and current ecological factors affecting species.
Includes hydrodynamics, reproduction, behavior, physiology, gene flow, and environmental conditions.
Importance of Biogeography
Biogeography is crucial for:
Understanding animal distribution.
Biodiversity conservation and planning (e.g., marine reserves).
Assessing impacts of climate change on species distributions.
Managing invasive species and natural resource management (e.g., fisheries).
Major Zones Related to Depth in Marine Environments
Zones:
Benthic (seafloor) & Pelagic (water column).
Photic, Mesophotic, Aphotic zones.
Depth categorization:
Deep Sea: Below ~200 m or ~1000 m.
Bathyal: 1000-4000 m.
Abyssal: 4000-6000 m.
Hadal: 6000-11000 m.
Definitions of terms may vary; crucial for understanding marine biogeographic contexts.
Biogeographic Terms and Definitions
Biome: A large collection of flora and fauna occupying a major habitat (e.g., tropical rainforest, coral reef, desert).
Biogeographic Realms: Large areas where biotas are internally coherent at higher taxonomic levels due to a shared evolutionary history.
Biogeographic Provinces/Regions: Distinct biotas exhibiting some level of endemism, influenced by historical and geographical isolation factors.
Delineation of Regions: Depends on:
Criteria used.
Types of data.
Taxonomic levels.
Geographic resolution.
Factors Influencing Biogeography:
Ocean currents.
Water masses.
Thermal, oxygen, depth, salinity, and nutrient gradients.
Environmental heterogeneity and ocean basin isolation (i.e., seafloor topography, continental positions).
Recent Assessments in Marine Biogeography
Marine Realms Analysis:
Studied 65,000 marine species and identified 30 marine realms, including:
18 continental shelf realms.
12 offshore + deep sea realms.
Unique Species Distribution: 42% of species unique to these realms, suggesting interconnected diversity across marine landscapes.
Major Patterns Influencing Biodiversity
Three Key Factors of Marine Biodiversity:
Temperature: Higher in tropics, influencing mutation rates and competition.
Productivity: Higher in coastal areas, contributing to larger populations.
Decreases from coastal seas to deep sea.
Nutrient-rich areas sustain higher primary production (PP).
Habitat Complexity/Heterogeneity: Greater heterogeneity supports more biodiversity due to microhabitat availability.
Depth and its Influence on Marine Life
General trends include:
Decreasing abundance and biomass with depth, except for bacteria.
Deep-sea environments tend to be food-limited, relying on sinking organic materials (marine snow).
Species diversity correlates with temperature, productivity, and habitat complexity, all of which decrease with depth.
Light and Temperature Gradients
Light Penetration:
Red light is absorbed; blue/green light penetrates furthest, influencing photosynthesis levels.
Temperature:
Thermocline separates mixed surface waters from deeper, more stable waters.
Salinity and Pressure Gradients
Salinity:
Varies globally and is influenced by freshwater input and evaporation rates.
Water Pressure:
Increases with depth, creating significant physiological challenges for marine life at greater depths.
Ocean Currents and Dispersal
Ocean currents serve as both highways and barriers:
Facilitate extensive dispersal over thousands of kilometers.
Can isolate species and regions, influencing patterns of biogeography.
Barriers to Marine Biogeography
Mid-Ocean Ridges: Linear mountain chains acting as barriers to benthic and deep-sea species.
Panama Isthmus: Historical vicariance event leading to allopatric speciation.
Red Sea: A mix of soft and hard barriers creating distinctive endemicity.
Mediterranean Sea: Hydrographically isolated, high salinity influencing species distribution.
Invasive Species and Human Impact
Invasive Species and Ship Ballast:
Transportation of aquatic species through ballast water presents a critical threat to biodiversity.
Over 300 species have been identified transferring from the Red Sea to the Mediterranean.
Natural Events: Tsunamis can lead to biological rafting events, significantly altering species distributions.