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Spatial distributions The distribution of of communities communities Part I: Community structure and gradients Outline Part I: 1. Basic definitions 2. Community function – energy 3. Spatial patterns Part II: 1. Terrestrial classifications 2. Aquatic classifications Basic definitions Population Group of inter-breeding individuals of a particular species Metapopulation set of local populations of a species that are linked by dispersal among those population (e.g. source-sink) Basic definitions Community • Assemblage of interacting organisms that share the same habitat • Boundaries – sharp or diffuse; somewhat arbitrary – ecotone: transition zone between communities Basic definitions Ecosystem • A set of abiotic and biotic components interacting in a given environment • Emphasizes function Basic definitions Biome • A defined area of similar climate and vegetation type; it may contain different taxa in different regions • Defined by physiognomy, leaf type, plant density • Highlights the role of the physical environment in determining characteristics of species assemblages Biomes Soil types Climate Soil type and climate are strong determinants of global biome distribution Hierarchy Community Organization: an energetic perspective How do species’ characteristics (niche) affect community organization? • Body size • Trophic level Body size : 1. Larger organisms require more energy 2. Smaller organisms require more energy per unit 3. Larger organisms generally have a greater capacity to withstand prolonged stress (higher storage reserves) Size influences scale of environment used by organism Fine-scale heterogeneity Landscape-scale heterogeneity Based on these principles, can one defined geographic area support more large or small species? Community Organization Trophic Level (how organisms acquire energy) Primary producers – produce biomass from inorganic compounds (autotrophs or chemoautotrophs) Herbivores/primary consumers – organisms that eat a plant-based diet (heterotrophs). Carnivore/secondary consumers – organisms that get nutrition from animal tissues (heterotrophs) Detritovores – consume detritus (heterotophs) Community Organization Trophic Level (how organisms acquire energy) 0.1-10% 0.1-10% 0.1-10% Community Organization Trophic Level (how organisms acquire energy) Less energy available to higher trophic levels • Smaller carrying capacity • Fewer species • Larger and more generalized Why are there rarely more than 5 trophic levels? Spatial Patterns Example: intertidal zone Ecotone: Zone of transition between two habitats or communities Spatial Patterns • Narrow ecotones can occur with abrupt environmental change (e.g. lake shore) – Species likely limited to one community • Wide ecotones – often occur with gradual transitions between more similar communities – May support species from both communities – May support ecotone specialists – Can have high species richness Ecotone specialists Environmental gradient Theoretical distributions of species along an environmental gradient Robert Whittaker 1975 Which figures show examples of competitive exclusion of species? Why? Robert Whittaker 1975 Which figures show examples of coevolved species? Why? Robert Whittaker 1975 Spatial Patterns Distribution of trees along an elevation gradient in the Sierra Nevada (CA) Biological interactions or physical factors? Yeaton 1981 So… what’s the typical pattern? • Species typically replace each other gradually along smooth environmental gradients but • When species with similar niches come into contact, sharp boundaries can be observed due to competitive exclusion • Sharp boundaries can also result from abrupt changes in environmental conditions (i.e. lake shore) Spatial distributions of communities Part II: Classifications Classifying communities • Difficult to classify communities into discrete units - do not represent discrete associations of species in space/time • But…humans like to classify • Quantitative patterns - multivariate statistical techniques used to quantify degree of similarity between two communities – Climate and soil have strong effect on types of plants in a region Whittaker 1975 Terrestrial Vegetation Types • • • • • • • Forest Woodland Shrubland Scrub Grassland Desert Tundra Temperate Forest • Evergreen and deciduous forests • Dry & wet temperate forests Tropical Forest •Mainly broadleaf dominated •Decidous dry forests •Evergreen rainforests Adaptation of species to low soil nutrients • Buttressing of dominant plants – Shallow roots stretch over surface, buttressing increases stability and increase flow of dissolved nutrients – Convergent architecture Adaptation of species to variations in solar radiation UV-shielding leaf cuticle on sun leaves and shade leaves (Krause et al. 2003) Adaptation of species to variations in solar radiation Understory plants – large broad leaves Epiphytes – plant that grows on another plant (non-parasite) Woodland Dominated by trees, but individuals are spaced and do not form a continuous canopy Example: Tropical Savannas (some savannas are classified as shrublands) Adaptation of species to drought Grasses – rapid growth during wet periods, water and nutrient storage in roots during dry periods Taproots – enlarged straight tapering root that grows vertically Trees store water in trunks, roots Adaptation of species to fire Perennial grasses – have rhizomes and can resprout (some have argued this is an adaptation to herbivory) Thick bark – protect vascular tissue from heat damage Baobab (Adansonia) Africa, Australia, Madagascar Long-lived Water storage in trunk Tap root Deciduous Fire-resistant bark Shrubland Continuous layer of shrubs, up to several meters high Example: Chaparral (sclerophyllous) Adaptation of species to drought Sclerophyllous – “sclero” = hard, phyll = leaf Leaves – hard, thick, leathery, small (minimize moisture loss) Chamise (Adenostoma fasciculatum) Evergreen chaparral shrub native to California (2-12 ft tall) Extensive root system (including taproot) Fires generally occur frequently (e.g. 10-40 yrs) Volatile secondary chemicals promote fire Resprouts Heat stimulates seed germination Scrub Shrubby individuals widely spaced Example: Coastal sage scrub, coastal California Adaptations to drought Soft wax-covered leaves reduce moisture loss Drought-deciduous leaves Grassland Dominated by grasses and forbs Example: Temperate grasslands/Great Plains Fire and grazing Grasses grow from nodes (not tips) Many species have rhizomes Grazers can be selective – altering species community Bison as a keystone species N availability higher in grazed areas Knapp et al 1991 Bison as a keystone species Grass photosynthesis higher in grazed areas Knapp et al 1991 Bison as a keystone species grazed ungrazed Knapp et al 1991 Great Plains grasslands evolved under influence of bison (Bison bison) but currently dominated by cattle (Bos taurus) • What are the differences in the grazing behaviors of bison and cattle in a tall grass prairie? (Allred et al. 2011) • Methods: Collared bison and cattle with GPS and monitored locations • Results: – Cattle – preferred riparian zones – Bison – not limited by proximity to water • Implications: cattle in riparian areas may alter vegetation (reduced veg cover, decreased productivity) Desert Most of the ground without vegetation; widely spaced individuals Example: Mohave Desert Adaptations to heat and drought Thick cuticle Spines, hairs (reflect solar radiation) Self-shade (pines, leaves) Water storage Shallow root system Joshua tree (Yucca brevifolia) Rapid initial growth Deep, extensive root system Narrow, waxy leaves Tundra Treeless biome under stressful environmental conditions Example: Alpine tundra Adaptations to cold and dry Mats or cushion growth form Dwarf shrubs Dark and hairy (absorb/trap heat) Tap roots Aquatic communities Physical factors that affect aquatic organisms are different than terrestrial systems – Three-dimensional space – Less temporal variation in temperature – Variations in salinity, light, pressure, water movement, nature of substrate Aquatic communities • Marine (oceanographers)– salinity varies ~ 35 ppt • Freshwater (limnologists) – salinity usually < 0.5 ppt Green Lakes Valley, CO Marine community classification • 1.37 billion cubic km in volume • Temperature, light, pressure, substrate • Marine classification – primarily based on water temp Arctic subarctic Northern temperate Northern sub-tropical Tropical Southern sub-tropical Southern temperate subantarctic Antarctic Marine community classification Photic zone – “well lit” Boundary is somewhat arbitrary, but usually set where light is less than 1-10% of incident solar radiation. Deepens with distance from coast Important ecologically Aphotic zone Hydrothermal tube worms – symbiotic relationship with chemosynthetic bacteria to produce organic compounds in the Galapagos Rift Marine community classification Bathymetry – depth and configuration of ocean bottom 1. Intertidal 2. Neritic 3. Bathyal 4. Abyssal Marine Organism Classification Benthic – organisms associated with a substrate Pelagic – open water organisms Freshwater Community Classification Lotic – flowing water (streams, rivers) Rapids/riffles – higher water velocity (high oxygen, rocky bottom) Pools – deep, slow-moving water (silty and poorly oxygenated bottoms) Clinger Mayfly larvae Rainbow trout Swimmer mayfly larvae Freshwater Community Classification Lentic – standing water (lakes, ponds) Littoral – light penetrates to bottom (rooted veg) Limnetic – offshore water that light penetrates for effective photosynthesis (phytoplankton) Profundal – beyond depth of effective light penetration Freshwater Community Classification Lentic – standing water (lakes, ponds) Eutrophic – ample/excessive nutrients, often shallow, warmer, lower oxygen content, subject to algal blooms (high primary productivity) Oligotrophic – low nutrient content, higher oxygen at depth (colder), lower primary productivity Eutrophication - Table Rock Lake, Missouri Freshwater Communities Rare community - Hypersaline Lake Example: Great Salt Lake