Lec. 10 pt. 1: Comprehensive Study Notes on Biogeography and Terrestrial Biomes
Species Richness, Taxonomy, and Identification in Biogeography
General Scope of Biogeographical Study: Much of biogeography focuses on species richness, which is defined as the absolute count of various species identified within a specific area.
The Incompleteness of Biodiversity Knowledge: * There is no location on Earth where every single species present is known to science. * On a university campus, while large mammals like deer are well-documented, smaller organisms remain undiscovered. * Examples of unidentified or under-studied organisms on campus include Rotifers, Nematode species, and various Fungi. * Specific recent discoveries on the speaker's campus include: * Two new species of Tardigrades. * One new crawfish parasite.
Taxonomic Disparities in Documentation: * Mammals: Generally well-known, though new species are occasionally described. Many "new" mammals are the result of taxonomic "splitting" (dividing one known species into two), but genuinely new, small mammals (like rodents or small herps) are sometimes discovered. * Insects: Contain a vast majority of identified species. * The top five orders for species richness are all within the Insecta class. * Coleoptera (Beetles): Comprise approximately of all identified species globally. * Weevils: Represent of all beetle species, with over known species and many more awaiting discovery. * Other Groups: Plants are highly diverse, sometimes exceeding individual insect orders. Poorly understood groups include Bacteria (where the very definition of a "species" is debated), Fungi, and Protists.
Temporal Patterns in Species Richness: * Richness fluctuates over "deep time" (geological time). * Mass extinctions cause significant drops; the fossil record shows fluctuations across families and species. * Current scientific consensus suggests species richness is likely higher in the modern Cenozoic era than at any other period in Earth's history, based on the long-term trends visible in the fossil record.
Geological Context: The speaker mentions being technically in the Holocene era, though the concept of the "Anthropocene" is noted. The Pleistocene was also referenced in previous lectures.
Ecological Niche Theory and Interspecific Competition
The Concept of the Niche: * The most prevalent definition of the niche was formulated by George Evelyn Hutchinson (who used the middle name Evelyn). * The N-Dimensional Hypervolume: A niche is an abstract concept composed of multiple axes (dimensions) representing the conditions and resources a species requires or tolerates. * Axes Factors: 1. Physical Conditions: Temperature ranges, humidity levels, etc. 2. Resources: Food size, nutrient availability, etc. * For a species to inhabit an area, every relevant axis must be within the satisfactory range for that organism.
Specialization vs. Generalization: * Specialists: Have very narrow ranges on their niche axes (e.g., diet specialists who eat only one thing, or organisms that can only survive in freshwater). * Generalists: Have wide tolerance ranges (e.g., species surviving in both saltwater and freshwater).
Biological Limiters of the Niche: * While resources and conditions define the niche, biological interactions can prevent a species from occupying an area it is physiologically capable of inhabiting. This is illustrated by the quote: "The rabbits may be a part of a coyote's niche, but coyotes are not part of a rabbit's niche. They're just something rabbits have to deal with." * Interaction Types: * Parasites: High loads may exclude a host. * Predators: Can completely exclude a prey species from a habitat. * Interspecific Competitors: Different species using the same limited resource.
Competitive Evolution: * Competition is biologically negative () for both parties; natural selection favors traits that reduce this overlap. * Niche Partitioning: Evolution to subdivide the environment. * Example: Robert MacArthur (Hutchinson's student) studied birds in Wisconsin forest trees. While they appeared to share the same trees, they subdivided the canopy into specific regions to reduce competition. * Character Displacement/Physical Changes: Evolution of body parts related to feeding. * Example: Middle Eastern and African small wild cats (including Felis sylvestris, the ancestor of the domestic cat and inspiration for "Sylvester the Cat"). These cats show minimal overlap in tooth size, allowing them to target different prey sizes and coexist.
Metabolism, Body Size, and Geographical Range
Metabolic Dynamics: * Metabolic rates vary significantly with body size. Larger animals generally have higher total metabolic rates but lower metabolic rates per unit mass. * Homeotherms (Endotherms): "Warm-blooded" animals have much higher metabolic rates because they spend a vast majority of their energy maintaining constant internal core temperatures. * Energy Storage: Small organisms have a limited ability to store energy compared to large organisms, affecting their response to seasonal environmental changes.
Size Distribution: * Body mass distributions for groups like mammals, birds, and beetles tend to be "humped" (unimodal) rather than a straight line. * The overall distribution of terrestrial animals is skewed to the left (smaller sizes) because insects comprise the majority of species and are generally small.
Geographical Range Patterns: * Small Mammals: Can have either very small or very large species ranges. * Large Mammals: Generally must have large species ranges to support their metabolic and resource needs; they rarely have small ranges. * Trophic Influence on Range: Carnivores tend to have larger ranges than herbivores of the same size because they exist at a higher trophic level, where energy is less abundant.
Trophic Structure: Food Chains, Webs, and Energy Pyramids
Trophic Levels: Derived from the Greek word for "eating." 1. Producers (Autotrophs): The base of all food chains. They utilize photosynthesis or chemosynthesis to convert inorganic energy ( and sunlight/chemicals) into organic molecules. 2. Consumers: Organisms that eat producers or other consumers.
Apex Predators: Also known as top predators. These are organisms at the top of a predatory food chain with no natural predators specialized in hunting them (e.g., Tigers, Killer Whales).
Food Chain Constraints: Food chains are limited in length (usually to levels in terrestrial systems) because energy is lost at each step. * Hyperparasitism: Parasites can have their own niche food chains (parasites of parasites), but these still trace back to the primary producer.
Food Webs: Highly complex interconnections of multiple food chains. No one has successfully mapped every species in a complex habitat like a tropical rainforest.
Specific Types of Food Chains: * Predatory: Moving from producers to herbivores to carnivores. * Detrital: Starting with dead organic material (Detritus). * Allochthonous Input: Energy coming into a community from a different community. For example, streams receive most of their energy from falling leaves rather than internal photosynthesis.
Laws of Thermodynamics and the Rule: * Available energy must decrease after every reaction. * Respiration Loss: Energy used for metabolic living (respiration) is unavailable to the next trophic level. * Production: Only energy used for growth and reproduction is passed on. * Efficiency: Endotherms (mammals/birds) are inefficient, spending of energy on maintaining body temperature. Tigers must eat daily, whereas a Python can wait months between meals because its metabolism drops. * The Average: On average, only of energy is transferred from one level to the next. This creates a pyramid where energy diminishes rapidly, explaining why food chains cannot be infinitely long (e.g., steps).
Carrying Capacity ()
Definition: The maximum number of individuals of a species that an environment can support indefinitely based on available resources (food, space, etc.).
Resource Predictors: In some areas, the number of squirrels is predicted by the abundance of acorns. Oak trees fluctuate acorn production ("masting") to control squirrel populations.
Population Dynamics: Populations may "overshoot" carrying capacity, but this is followed by a die-off as the resource base cannot sustain the numbers.
Human Application: The carrying capacity of Earth for humans is a subject of debate, with estimates ranging from current levels to , , or even people.
General Ecological Rules: * Small Animals: Need fewer resources per individual, tend to be specialists, have higher carrying capacities (), higher species richness, and can exist in smaller ranges. * Large Animals: Require more food/space, tend to be generalists (less picky to meet high caloric needs), occupy higher trophic levels, have lower carrying capacities/fewer species, and require larger ranges.
Terrestrial Biomes: Definition and Determinants
Biome Definition: The highest unit of terrestrial community, defined by the dominant vegetation types (rather than animals).
Biomes vs. Zoogeographical Realms: Biomes are ecological (based on climate/plants), whereas realms (e.g., Nearctic) are based on evolutionary history and continental movement.
Primary Determinants of Biomes: 1. Temperature Regime: Seasonal patterns and averages. 2. Precipitation Regime: Total rainfall and its annual distribution. * Secondary factors: Soil types and "keystone species" may affect boundaries at the margins.
Terminology: * Mesic: Habitats with moderate moisture and temperatures (e.g., many temperate forests). * Xeric: Extremely dry habitats (e.g., deserts, arid grasslands).
Global Survey of Terrestrial Biomes
Tropical Rainforests: * Located at equatorial latitudes. * Characteristics: High complexity, multiple canopy levels, high epiphytic growth (plants like Spanish moss that grow on other plants), and many vines. * The forest floor is often dark with poor soil.
Tropical Deciduous/Monsoon Forests: Found in drier tropical areas (e.g., parts of Ecuador or SE Asia); trees drop leaves due to seasonal dry spells rather than cold.
Temperate Deciduous Forests: * Found in mid-latitudes (e.g., Ohio, Michigan, parts of China and Europe). * Characterized by broad-leaf trees that drop leaves simultaneously in winter to conserve energy/water. * Very little original (old-growth) deciduous forest remains; the Białowieża Forest (Poland/Belarus) is one of the last original patches in Europe.
Temperate Rainforests: * Found in the Pacific Northwest (Washington, Oregon, British Columbia, Alaska). * High rainfall and massive trees, including Redwoods (tallest) and Sequoias (largest).
Boreal Forest (Taiga/Coniferous): * Vast northern hemisphere forests (Canada, Alaska, Scandinavia, Siberia). * Dominated by a few species of conifers (fir trees) that withstand harsh winters and limit water evaporation through needles. * Flowering plants (angiosperms) pushed conifers into these harsh environments where flowering plants cannot survive.
Sclerophyllous/Chaparral/Mediterranean Vegetation: * Characterized by "hard-leaved" (sclerophyllous) plants, shrubs, and low trees (e.g., olive trees). * Highly flammable; fire is a natural part of the ecosystem. * Geography: Mediterranean, California (Chaparral), South Africa (Fynbos - extremely diverse/endemic), and France (Maquis). * Cultural Note: Hollywood is in the heart of Chaparral country; early Westerns and even Star Trek episodes were often filmed in local California Chaparral, misrepresenting the look of the rest of the world (e.g., Kansas or other planets).
Grasslands: * Tropical Savannah: Tropical grasslands with scattered trees; high herbivore density (Africa). * Temperate Grasslands: * Tall Grass Prairie: Higher rainfall areas (most converted to corn/wheat fields). * Short Grass Prairie (Steppe): Drier areas, typically used for cattle grazing.
Deserts: * Occur in both temperate and tropical zones. * Types: * Sonoran: Higher rainfall, features Saguaro cacti. * Extreme Deserts: Sahara, Death Valley (rain every years). * Coastal Deserts: Namib or Atacama; plants and animals survive on dew from the ocean.
Tundra: * High latitude/Polar grasslands. * Permafrost: Permanently frozen subsoil prevents tree root growth. * Productive summer seasons with massive insect blooms and migratory birds. * Tree line: The northern limit where trees stop growing. It has been advancing north since the last ice age.
Human Impact and Anthropogenic Biomes
The Intersection of Biomes: South Louisiana exists at an intersection of multiple biome types.
Anthropogenic Biomes: Proposed by scientists like Erle Ellis and Navin Ramankutty. This concept overlays human impact (population density, agriculture, urbanization) on traditional biome maps.
Purple Zones: Represent high-impact human areas (cities, heavy agriculture) found in Western Europe, the NE United States, China, and India.
Questions & Discussion
Speaker’s Personal Background: The speaker shared their academic path, transitioning from a non-thesis Master's to teaching junior high for three years in Los Angeles, then returning to the University of South Florida for a PhD in marine ecology, specifically studying shallow-water marine invertebrates. Their interest in zoology was lifelong, beginning with a childhood interest in dinosaurs and later histology and embryology.
Student Question on Definitions: The speaker clarified that "deciduous" refers to the simultaneous dropping of leaves or teeth (deciduous teeth).
Student Question on Soil: A student asked if soil type determines biomes; the speaker acknowledged that soil and keystone species matter at local margins, but temperature and precipitation are the broad-scale determinants.