8.1 Nearctic realm
10 min read•august 21, 2024
The Nearctic realm, spanning North America north of Mexico, is a diverse biogeographic region with unique flora and fauna. From Arctic tundra to subtropical forests, it encompasses varied landscapes and ecosystems shaped by climate, geology, and evolutionary history.
This realm's biodiversity reflects complex interactions between environmental factors and biogeographic events. Understanding its characteristics, from climate patterns to ecological interactions, is crucial for conservation efforts and managing human impacts on these ecosystems.
Geographic extent of Nearctic
- Encompasses North America north of Mexico, including Greenland and parts of northern Mexico
- Represents one of Earth's eight major biogeographic realms, characterized by unique flora and fauna
- Spans diverse landscapes from Arctic tundra to subtropical forests, showcasing ecological variety
Boundaries and borders
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- Northern boundary extends to the Arctic Ocean, including Canadian Arctic Archipelago
- Southern limit reaches the Tropic of Cancer in Mexico, bordering the Neotropical realm
- Eastern border defined by the Atlantic Ocean, including offshore islands (Newfoundland)
- Western edge stretches to the Pacific Ocean, incorporating the Aleutian Islands
Major landforms and features
- form a prominent north-south mountain range, influencing climate patterns
- Great Plains occupy the central region, characterized by vast grasslands and prairies
- Appalachian Mountains in the east create diverse habitats and microclimates
- system represents the largest freshwater ecosystem in the realm
- Mississippi River basin serves as a major drainage system and biodiversity hotspot
Climate patterns
- Nearctic realm exhibits diverse climate zones due to its vast latitudinal extent
- Atmospheric circulation patterns, ocean currents, and topography influence regional climates
- Understanding climate patterns crucial for explaining biodiversity distribution and adaptations
Temperature gradients
- North-south temperature gradient ranges from polar to subtropical climates
- Arctic regions experience extremely cold winters and cool summers (average annual temperature below 0°C)
- Temperate zones have moderate temperatures with distinct seasons (average annual temperature 0-20°C)
- Subtropical areas in the south maintain warmer temperatures year-round (average annual temperature above 20°C)
- Elevation affects temperature, creating vertical climate zones in mountainous regions
Precipitation distribution
- Rainfall patterns vary significantly across the realm, influenced by topography and atmospheric circulation
- Coastal regions often receive higher precipitation due to moisture from oceans (Pacific Northwest)
- Rain shadow effect creates dry areas on leeward sides of mountain ranges (Great Basin)
- Continental interiors tend to be drier, with precipitation decreasing from east to west
- Monsoon systems influence precipitation in southwestern regions (North American Monsoon)
Seasonal variations
- Most of the realm experiences four distinct seasons due to Earth's axial tilt
- Winter brings snow and freezing temperatures to northern and high-elevation areas
- Spring and fall serve as transition periods with variable weather patterns
- Summer temperatures can reach extremes in continental interiors (Great Plains)
- Seasonal changes drive important ecological processes (migration, hibernation, leaf senescence)
Biomes and ecosystems
- Nearctic realm hosts a diverse array of biomes, each with unique plant and animal communities
- Biome distribution influenced by climate patterns, soil types, and geological history
- Understanding biome characteristics essential for comprehending biodiversity patterns
Tundra ecosystems
- Located in Arctic regions and high mountain areas, characterized by low-growing vegetation
- Permafrost underlies much of the tundra, limiting plant root growth
- Adapted plants include lichens, mosses, sedges, and dwarf shrubs
- Wildlife includes migratory birds, caribou, musk oxen, and Arctic foxes
- Short growing season and harsh conditions require specialized adaptations
Boreal forests
- Also known as taiga, dominated by coniferous trees (spruce, fir, pine)
- Extends across northern North America, forming Earth's largest terrestrial biome
- Long, cold winters and short, cool summers characterize the climate
- Wildlife includes moose, wolves, lynx, and numerous boreal bird species
- Plays crucial role in global carbon cycling and climate regulation
Temperate deciduous forests
- Found in eastern North America, characterized by broadleaf trees that shed leaves seasonally
- Four distinct seasons with warm summers and cold winters
- Diverse tree species (maple, oak, beech) create complex forest structures
- Rich understory vegetation and abundant wildlife (white-tailed deer, black bears)
- Historically modified by human activities, now fragmented in many areas
Grasslands and prairies
- Occupy central North America, dominated by grasses and forbs
- Includes tallgrass, mixed-grass, and shortgrass prairies
- Climate characterized by hot summers, cold winters, and variable precipitation
- Adapted fauna includes bison, pronghorn, prairie dogs, and grassland birds
- Fire plays a crucial role in maintaining grassland ecosystems
Deserts and xeric shrublands
- Located in southwestern North America, characterized by low precipitation and high temperatures
- Includes hot deserts (Sonoran, Chihuahuan) and cold deserts (Great Basin)
- Plants adapted to water scarcity (cacti, succulents) and extreme temperatures
- Unique fauna includes desert bighorn sheep, kangaroo rats, and various reptiles
- Specialized adaptations for water conservation and heat tolerance
Flora characteristics
- Nearctic flora exhibits diverse adaptations to varied climatic and environmental conditions
- Plant communities reflect complex interactions between climate, soil, and biogeographic history
- Understanding flora characteristics crucial for ecosystem management and conservation
Plant adaptations
- Cold tolerance mechanisms in boreal and tundra species (antifreeze proteins, dormancy)
- Drought resistance strategies in desert plants (deep roots, water storage tissues)
- Fire-adapted traits in grassland and forest species (thick bark, serotinous cones)
- Deciduous habit in temperate forests as adaptation to seasonal changes
- Symbiotic relationships with fungi and bacteria to enhance nutrient uptake
Endemic plant species
- California Floristic Province hosts numerous due to isolation and diverse habitats
- Serpentine soil areas support unique plant communities adapted to high metal concentrations
- Island endemics found on offshore islands (Channel Islands, Aleutian Islands)
- Relict species persisting in isolated habitats (Torrey pine, bristlecone pine)
- Evolutionary radiations in genera like Astragalus and Penstemon creating endemic species complexes
Vegetation zones
- Altitudinal zonation in mountain ranges creates distinct plant communities at different elevations
- Coastal vegetation zones influenced by salt spray, wind, and soil conditions
- Riparian corridors support unique plant assemblages along rivers and streams
- Transition zones (ecotones) between major biomes harbor diverse plant communities
- Edaphic factors create specialized vegetation zones (gypsum outcrops, limestone barrens)
Fauna diversity
- Nearctic realm supports a rich and diverse fauna, reflecting varied habitats and evolutionary history
- Understanding faunal diversity crucial for conservation planning and ecosystem management
- Biogeographic patterns influenced by historical factors, including glaciations and land bridge connections
Mammalian fauna
- Large herbivores include iconic species like bison, moose, and bighorn sheep
- Carnivore diversity represented by grizzly bears, wolves, mountain lions, and smaller predators
- Rodent fauna highly diverse, with numerous endemic species in different habitats
- Marine mammals along coastal areas include seals, sea lions, and various whale species
- Bat diversity highest in southern regions, with important roles in ecosystem services
Avian species
- Migratory birds utilize flyways connecting Nearctic breeding grounds to wintering areas
- Waterfowl diversity high in wetland and coastal habitats (ducks, geese, waders)
- Raptors include eagles, hawks, and owls adapted to various ecosystems
- Songbird communities show high diversity and specialization across different habitats
- Endemic bird species found on islands and in isolated mountain ranges
Reptiles and amphibians
- Highest diversity in southern regions with warmer climates
- Salamander diversity particularly high in Appalachian Mountains
- Unique adaptations for surviving cold climates in northern species (freeze tolerance)
- Desert reptiles show specialized adaptations for water conservation and thermoregulation
- Amphibian declines observed in many areas due to habitat loss and disease
Freshwater fish diversity
- Great Lakes system hosts diverse fish communities, including endemic species
- Salmonid species important in cold-water streams and lakes across the realm
- Mississippi River basin supports high fish diversity, including ancient sturgeon species
- Desert springs and isolated water bodies harbor unique endemic fish populations
- Diadromous fish species connect freshwater and marine ecosystems (salmon, eels)
Biogeographic history
- Nearctic realm's current biodiversity patterns shaped by complex geological and climatic history
- Understanding past events crucial for interpreting present-day species distributions
- Biogeographic history informs conservation strategies and predictions of future changes
Pleistocene glaciations
- Repeated ice ages during the Pleistocene epoch profoundly influenced Nearctic biogeography
- Laurentide and Cordilleran ice sheets covered much of northern North America
- Glacial refugia in ice-free areas preserved plant and animal populations
- Periglacial environments supported unique communities adapted to cold, dry conditions
- Glacial cycles drove speciation events and shaped genetic diversity patterns
Post-glacial recolonization
- As ice sheets retreated, plants and animals recolonized newly exposed habitats
- Rapid northward expansion of temperate species following warming trends
- Formation of new ecosystems as species reassembled in novel combinations
- Genetic evidence reveals recolonization routes and source populations
- Some species lagged behind climate change, creating disequilibrium distributions
Land bridge migrations
- Bering Land Bridge connected Nearctic and Palearctic realms during glacial periods
- Facilitated bidirectional migrations of plants and animals between continents
- Contributed to shared fauna between North America and Eurasia (bears, wolves)
- Allowed human migration into North America from Asia
- Intermittent connections created opportunities for allopatric speciation
Ecological interactions
- Complex ecological relationships shape Nearctic ecosystems and biodiversity patterns
- Understanding these interactions crucial for ecosystem management and conservation
- Ecological processes operate across multiple spatial and temporal scales
Predator-prey relationships
- Top predators like wolves and mountain lions influence herbivore populations and behavior
- Mesopredator release occurs when top predators are removed from ecosystems
- Prey species show various antipredator adaptations (camouflage, defensive structures)
- Predator-prey cycles observed in some systems (lynx-hare cycle in boreal forests)
- Indirect effects of influence plant communities and ecosystem processes
Keystone species
- Beavers act as ecosystem engineers, creating wetland habitats through dam-building
- Prairie dogs in grassland ecosystems increase habitat heterogeneity and biodiversity
- Sea otters in coastal ecosystems control sea urchin populations, protecting kelp forests
- Bison grazing patterns influence grassland plant community structure and fire regimes
- Pollinator species play crucial roles in maintaining plant diversity and ecosystem function
Trophic cascades
- Reintroduction of wolves in Yellowstone National Park altered elk behavior and vegetation patterns
- Sea otter recovery in coastal areas led to increased kelp forest cover and associated biodiversity
- Overfishing of sharks can lead to changes in prey fish populations and seagrass habitats
- Removal of large herbivores can alter plant community composition and fire regimes
- Understanding trophic cascades important for ecosystem restoration and management
Human impact
- Human activities have profoundly altered Nearctic ecosystems and biodiversity patterns
- Anthropogenic impacts operate across multiple scales, from local to global
- Understanding human influences crucial for developing effective conservation strategies
Habitat fragmentation
- Urbanization and agricultural expansion have fragmented many natural habitats
- Roads and other linear infrastructure create barriers to animal movement and gene flow
- Fragmentation increases edge effects and reduces habitat quality for interior species
- Isolated habitat patches may not support viable populations of some species
- Connectivity conservation aims to mitigate fragmentation effects through corridors and stepping stones
Invasive species
- Non-native species introductions have altered ecosystems across the Nearctic realm
- Invasive plants like kudzu and cheatgrass outcompete native species and alter habitats
- Introduced animals (feral hogs, Asian carp) impact native fauna and ecosystem processes
- Invasive insects and pathogens threaten native forests (emerald ash borer, chestnut blight)
- Economic and ecological costs of management are substantial
Conservation efforts
- Protected area networks aim to preserve representative habitats and species
- Endangered Species Act provides legal protection for threatened and endangered species
- Habitat restoration projects seek to recover degraded ecosystems and improve biodiversity
- Wildlife corridors and connectivity initiatives address issues
- Community-based conservation programs engage local stakeholders in biodiversity protection
Nearctic vs other realms
- Comparing Nearctic realm with other biogeographic regions reveals unique characteristics
- Understanding similarities and differences crucial for global biodiversity conservation
- Biogeographic comparisons inform studies of evolution, ecology, and biogeography
Similarities with Palearctic
- Both realms share similar latitudinal extent and climate patterns
- Many plant and animal genera common to both realms (pines, oaks, bears, deer)
- Comparable biome types present in both realms (tundra, , temperate forest)
- Similar ecological processes and adaptations to northern climates
- Historical connections via Bering Land Bridge facilitated species exchanges
Differences from Neotropical
- Nearctic realm has lower overall biodiversity compared to Neotropical realm
- Fewer endemic families and genera in Nearctic due to different evolutionary history
- Nearctic experiences more pronounced seasonality and colder winters
- Neotropical realm lacks extensive tundra and boreal forest biomes
- Different biogeographic history, with Nearctic more influenced by Pleistocene glaciations
Biogeographic subdivisions
- Nearctic realm can be further divided into smaller biogeographic units
- Subdivisions reflect differences in climate, vegetation, and faunal assemblages
- Understanding these divisions important for conservation planning and ecological research
Ecoregions of Nearctic
- World Wildlife Fund (WWF) recognizes numerous terrestrial ecoregions within Nearctic
- Major ecoregions include Arctic tundra, Northern forests, Great Plains, Eastern forests
- Each ecoregion characterized by distinct plant and animal communities
- Ecoregion classification based on climate, vegetation, geology, and species distributions
- Conservation strategies often developed at the ecoregion level
Transition zones
- Areas where different biomes or ecoregions meet, often with high biodiversity
- Prairie-forest ecotone in central North America supports mix of grassland and forest species
- Subtropical-temperate transition in southeastern U.S. creates unique plant communities
- Montane-lowland transitions along elevation gradients harbor diverse species assemblages
- Understanding transition zones important for predicting responses to climate change
Current threats
- Nearctic biodiversity faces numerous anthropogenic threats
- Understanding these threats crucial for developing effective conservation strategies
- Many threats operate synergistically, compounding their impacts on ecosystems
Climate change effects
- Shifting temperature and precipitation patterns alter species distributions and phenology
- Arctic and alpine ecosystems particularly vulnerable to warming trends
- Sea level rise threatens coastal habitats and species
- Increased frequency and intensity of extreme weather events (droughts, hurricanes)
- Climate change interacts with other stressors, exacerbating their impacts on ecosystems
Urbanization and development
- Rapid urban expansion leads to habitat loss and fragmentation
- Increased impervious surfaces alter hydrological cycles and create urban heat islands
- Light pollution from urban areas affects nocturnal species and migration patterns
- Urban-wildland interfaces create new ecological dynamics and management challenges
- Green infrastructure initiatives aim to mitigate negative impacts of urbanization
Pollution and habitat loss
- Agricultural runoff contributes to eutrophication of aquatic ecosystems
- Industrial pollutants contaminate air, water, and soil, affecting wildlife health
- Plastic pollution in marine and freshwater systems impacts aquatic species
- Habitat loss due to resource extraction (mining, logging) threatens biodiversity
- Cumulative effects of multiple pollution sources create complex environmental challenges
Key Terms to Review (18)
American Bison: The American bison is a large mammal native to North America, known for its massive build, shaggy fur, and distinctive hump on its shoulders. As a keystone species, the American bison plays a crucial role in the Nearctic realm's grassland ecosystems, influencing plant community dynamics and providing habitat for various other species.
Biogeographic barriers: Biogeographic barriers are physical or biological obstacles that restrict the movement and distribution of species across geographical areas. These barriers can include mountains, rivers, oceans, and even climate factors that limit how organisms disperse and colonize new habitats. Understanding these barriers is crucial in explaining disjunct distributions of species and the distinct characteristics of various biogeographic realms.
Boreal forest: The boreal forest, also known as taiga, is a biome characterized by coniferous forests primarily found in the high northern latitudes, stretching across Canada, Alaska, Russia, and Scandinavia. This ecosystem plays a vital role in carbon storage and influences global climate patterns, while also serving as critical habitat for diverse wildlife species adapted to its cold and often harsh environment.
Continental drift: Continental drift is the theory that the Earth's continents have moved over geological time, shifting positions relative to one another. This movement is primarily due to the processes associated with plate tectonics, leading to significant changes in climate, sea levels, and the distribution of species across the globe.
Eastern white pine: The eastern white pine (Pinus strobus) is a tall, coniferous tree native to eastern North America, recognized for its straight trunk, soft needles, and long cones. This species plays a significant role in forest ecosystems and has substantial historical and economic importance due to its timber quality and versatility.
Endemic species: Endemic species are organisms that are native to and restricted to a specific geographical area. These species have evolved over time in isolation, making them unique to their environment and often vulnerable to changes such as habitat loss or climate change.
Great Lakes: The Great Lakes are a group of five large freshwater lakes located in North America, specifically along the Canada-United States border. These lakes—Superior, Michigan, Huron, Erie, and Ontario—are the largest group of freshwater lakes by total area in the world, and they play a crucial role in the ecology, economy, and climate of the surrounding regions.
Habitat fragmentation: Habitat fragmentation refers to the process in which larger habitats are divided into smaller, isolated patches, often due to human activities like urban development, agriculture, and infrastructure projects. This division can significantly affect biodiversity, species interactions, and ecosystem functions, as it alters the landscape and limits the movement of organisms between habitat patches.
Humid continental: Humid continental refers to a climate classification characterized by significant seasonal temperature variations, with warm to hot summers and cold winters, typically found in the mid-latitudes. This climate is known for its distinct seasons and is influenced by the surrounding geography, such as mountains and bodies of water, which impact precipitation patterns and temperature extremes.
Invasive Species: Invasive species are organisms that are introduced to a new environment, where they can spread rapidly and outcompete native species, often causing ecological, economic, and health issues. Their presence can disrupt local ecosystems, altering biogeographical processes and patterns as they establish themselves in various regions.
Mutualism: Mutualism is a type of interaction between two species where both parties benefit from the relationship. This ecological partnership is essential for many organisms, influencing community structure and biodiversity. It can involve various forms, such as pollination, seed dispersal, and nutrient exchange, playing a critical role in ecosystem functioning and resilience.
Pleistocene Glaciation: Pleistocene glaciation refers to a series of glacial and interglacial periods that occurred during the Pleistocene epoch, approximately 2.6 million to 11,700 years ago. This era was marked by significant climate changes that led to the expansion of ice sheets across North America, Europe, and Asia, profoundly impacting the distribution of flora and fauna. The effects of these glaciations can still be observed today in various realms, influencing species diversity, habitat formation, and evolutionary processes.
Predation: Predation is a biological interaction where one organism, the predator, kills and eats another organism, the prey. This relationship is crucial in shaping ecological dynamics, influencing population sizes, and promoting biodiversity through various biogeographical processes and community interactions.
Primary Succession: Primary succession is the process of ecological change that occurs in an environment that is devoid of life, such as after a volcanic eruption or glacial retreat. This process begins with the colonization of bare rock or barren land by pioneer species, which are capable of surviving in harsh conditions and ultimately lead to the establishment of a stable ecosystem. The duration of primary succession can vary greatly, making it important for understanding temporal scales in biogeography, particularly how ecosystems evolve over time. Additionally, this concept can be related to specific regions, like the Nearctic realm, where primary succession might occur after disturbances such as forest fires or land clearing.
Rocky Mountains: The Rocky Mountains, often referred to as the Rockies, is a major mountain range in North America that stretches over 3,000 miles from Canada to New Mexico. This range is characterized by its stunning landscapes, rich biodiversity, and significant geological features, making it a vital part of the Nearctic realm's ecological system.
Secondary succession: Secondary succession is the process by which ecosystems recover and rebuild after a disturbance, such as fire, flood, or human activity, that leaves the soil intact. Unlike primary succession, which starts from bare rock or uninhabited areas, secondary succession begins in areas where a biological community has previously existed but has been disturbed. This recovery can occur over shorter time scales due to existing soil and seed banks, making it a key concept in understanding how ecosystems respond to change over time.
Semi-arid: Semi-arid refers to a climate characterized by low rainfall, typically between 10 to 20 inches (250 to 500 mm) annually, which results in a landscape that is drier than humid areas but still supports some vegetation. This climate zone often features temperature extremes, with hot summers and cool winters, making it a crucial area for understanding biodiversity and ecosystem dynamics.
Temperate grassland: Temperate grasslands are ecosystems characterized by vast open spaces dominated by grasses, with few trees or shrubs. These areas experience moderate rainfall, making them distinct from deserts and forests, and are crucial for agriculture and biodiversity, especially in regions like the Nearctic realm. The presence of periodic disturbances, such as fires and grazing, plays a vital role in maintaining the health and diversity of these ecosystems.