🦕Paleoecology Unit 11 – Paleoecology: Patterns and Adaptive Radiations

Key Concepts and Definitions

• Paleoecology studies the interactions between ancient organisms and their environments using fossil evidence
• Adaptive radiation rapid diversification of a single ancestral species into a wide variety of new forms
  • Occurs when a species encounters a new ecological opportunity or enters a new environment
• Paleoenvironment the environment that existed at a particular time in the geologic past
• Taphonomy the study of how organisms decay and become fossilized
• Biostratigraphy the correlation and classification of rock strata based on the fossil assemblages they contain
• Paleoecological reconstruction the process of inferring the ecology of ancient organisms and their environments based on fossil evidence
• Convergent evolution the independent evolution of similar features in species of different periods or epochs in time
• Ecological niche the role and position a species has in its environment how it meets its needs for food and shelter, how it survives, and how it reproduces

Geological Time Periods Covered

• Paleozoic Era (541 to 252 million years ago) includes the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian periods
  • Characterized by the diversification of marine invertebrates, fish, amphibians, and early reptiles
• Mesozoic Era (252 to 66 million years ago) includes the Triassic, Jurassic, and Cretaceous periods
  • Characterized by the dominance of dinosaurs and the evolution of birds and mammals
• Cenozoic Era (66 million years ago to present) includes the Paleogene, Neogene, and Quaternary periods
  • Characterized by the evolution and diversification of mammals, birds, and flowering plants
• Pleistocene Epoch (2.6 million to 11,700 years ago) a time of repeated glaciations and the evolution of humans
• Holocene Epoch (11,700 years ago to present) the current interglacial period marked by the development of human civilizations

Major Adaptive Radiations

• Cambrian Explosion (541 million years ago) rapid diversification of animal phyla in the early Cambrian period
  • Gave rise to most major animal body plans and laid the foundation for future evolutionary radiations
• Great Ordovician Biodiversification Event (GOBE) significant increase in marine biodiversity during the Ordovician period
• Mesozoic Marine Revolution (MMR) (150 to 50 million years ago) increase in the diversity and ecological importance of marine predators
  • Led to changes in marine ecosystems and the evolution of new defensive strategies in prey species
• Mammalian radiation after the Cretaceous-Paleogene (K-Pg) extinction (66 million years ago)
  • Diversification of mammals following the extinction of non-avian dinosaurs
• Neotropical rainforest diversification during the Cenozoic
  • Adaptive radiation of plants and animals in response to the formation of the Amazon and other neotropical rainforests

Paleoenvironmental Reconstruction Methods

• Stable isotope analysis uses the ratios of stable isotopes (e.g., carbon, oxygen) in fossils to infer past climates and environments
• Palynology the study of fossil pollen and spores to reconstruct past vegetation and climates
• Paleosol analysis examines ancient soils to infer past climates, vegetation, and landscapes
• Biomarker analysis uses organic compounds preserved in sediments to reconstruct past environments and ecosystems
• Fossil assemblage analysis studies the composition and diversity of fossil communities to infer past ecological relationships and environments
• Geochemical proxies (e.g., trace elements, biomarkers) provide information about past ocean conditions, productivity, and oxygenation
• Sedimentological analysis examines the physical and chemical properties of sediments to infer past depositional environments and climates

Case Studies and Examples

• End-Permian mass extinction (252 million years ago) the largest known mass extinction event in Earth's history
  • Caused by a combination of factors, including volcanic eruptions, climate change, and ocean acidification
  • Led to the extinction of ~96% of marine species and ~70% of terrestrial vertebrate species
• Eocene-Oligocene transition (34 million years ago) a global cooling event that led to the expansion of grasslands and the evolution of grazing mammals
• Pleistocene megafaunal extinctions (50,000 to 10,000 years ago) the extinction of large mammals (e.g., mammoths, ground sloths) at the end of the last ice age
  • Likely caused by a combination of climate change and human hunting
• Paleocene-Eocene Thermal Maximum (PETM) (56 million years ago) rapid global warming event caused by the release of carbon into the atmosphere
  • Led to changes in ocean circulation, extinctions, and the migration of species to higher latitudes
• Great American Biotic Interchange (GABI) (~3 million years ago) exchange of fauna between North and South America following the formation of the Isthmus of Panama

Ecological Patterns Through Time

• Latitudinal diversity gradient the observation that species diversity tends to increase from the poles to the equator
  • Has been a persistent pattern throughout Earth's history, but the steepness of the gradient has varied over time
• Phanerozoic trends in global biodiversity show an overall increase in diversity over the past 541 million years
  • Punctuated by periodic mass extinctions followed by recovery and diversification
• Onshore-offshore gradient in marine biodiversity the trend of decreasing species diversity from shallow coastal areas to the deep ocean
• Ecological state shifts occur when an ecosystem undergoes a rapid, nonlinear change in response to a perturbation or gradual change in conditions
  • Can be identified in the fossil record by abrupt changes in community composition and structure
• Biotic interactions (e.g., predation, competition) shape the structure and diversity of communities over time
  • Can lead to co-evolutionary arms races and the evolution of new adaptations and ecological strategies

Research Techniques and Tools

• Quantitative paleoecology applies statistical and computational methods to analyze fossil data and test hypotheses about past ecological processes
• Morphometrics the quantitative analysis of shape and size variation in fossils
  • Used to study evolutionary trends, adaptations, and ecological relationships
• Phylogenetic comparative methods use evolutionary relationships among species to study the evolution of ecological traits and interactions
• Ecological network analysis studies the structure and dynamics of ecological networks (e.g., food webs) in the fossil record
• Geochemical techniques (e.g., stable isotope analysis, trace element analysis) provide insights into the diets, habitats, and physiologies of ancient organisms
• Computational modeling simulates past ecological processes and interactions to test hypotheses and generate predictions
• High-resolution sampling and dating techniques allow for the reconstruction of ecological and evolutionary processes at fine temporal scales

Implications for Modern Ecology

• Understanding past ecological responses to environmental change can inform predictions about future responses to climate change and other anthropogenic pressures
• Studying past biotic interactions and ecological networks can provide insights into the assembly and functioning of modern ecosystems
• Paleoecological data can be used to establish baseline conditions and natural ranges of variability for conservation and restoration efforts
• Investigating the ecological and evolutionary consequences of past mass extinctions can help predict the potential impacts of current and future biodiversity loss
• Combining paleoecological and neontological data can provide a more comprehensive understanding of ecological and evolutionary processes across timescales
• Paleoecological research can identify long-term ecological trends and patterns that may not be apparent from short-term studies of modern ecosystems
• Insights from paleoecology can inform the management and conservation of modern species and ecosystems in the face of global change