Community Structure – Concepts & Diversity – 2021 PDF

Community Structure – Concepts & Diversity Copyright © 2021 W. H. Freeman and Company. All rights reserved. Communities can have distinct or gradual boundaries. Santa Catalina Mountains, Arizona Gradual Zones in Terrestrial Communities Rocky shores of Northeastern England Gradual Zones al...

Community Structure – Concepts & Diversity Copyright © 2021 W. H. Freeman and Company. All rights reserved. Communities can have distinct or gradual boundaries. Santa Catalina Mountains, Arizona Gradual Zones in Terrestrial Communities Rocky shores of Northeastern England Gradual Zones along Ocean Shorelines  Sharp Boundaries at Ecotones Aspen “Edge species” Goldenrod Serpentine Soils & Ecotones Serpentine Soils  A Line Transect of Serpentine and Non- serpentine Soils Local Example of Ecotone Cedar Glades of middle TN  “Schools” of Community Philosophy 1920s Interdependent (“Super-organism”) Independent Henry Gleason Frederic Clements New York Botanical Garden U. of Nebraska Carnegie Inst. of Washington Where do we stand today?  Independent Distribution of Trees Mount LeConte Interdependence of Species under Extreme Environmental Conditions Established experiments over the globe Tundra Alpine tundra (stressful Subalpine forest – high elevation) Subalpine forest (low elevation) Neighbor removal experiment Control: Treatment with target species: What happens when you remove neighbors? Low vs. high elevation What do the responses indicate? Low vs. high elevation Facilitation (nurse plants) in (stressful) Deserts Soil water Herbivory Community incorporates both the number and relative abundance of species.  Concepts Species richness Species evenness Log-normal Distributions of Species Abundance Log-normal Distributions – Dependent on Sample Size  Species Diversity What is Diversity? More species and more nearly equal their abundances  greater the diversity Which community is more diverse – 1 or 2 ?  Species Diversity Indices Simpson’s index S = species richness pi = relative abundance of each species in the community Shannon’s index (H’) is also known as the Shannon-Wiener index Species Diversity Commun Simpson Shanno ity ’s index n’s index 1 4 1.38 2 1.53 0.71 Species diversity is affected by: 1. Resources – Nutrients, Light 2. Habitat Diversity 3. Keystone Species 4. Disturbance Fertility Effects on Species Richness Park Grass Experiment Started 1856 Original purpose: improve hay production with fertilizers Fertility Effects on Species Richness Reversing the Effects of Added Nutrients on Species Richness Dominant species Reversing the Effects of Added Nutrients on Species Richness Dominant species vs Small (shade intolerant) species Reversing the Effects of Added Nutrients on Species Richness High Diversity Ecosystems Have Low Nutrients Diversity Biome High Tropical rainforests Sclerophyllous woodlands (or shrublands) Low Temperate seasonal forests Why Poor Places Are More Diverse? https://www.youtube.com/watch?v=mWVATekt4ZA Habitat Diversity and Species Diversity Keystone Species Keystone Sea Stars as a Keystone Predator Another Example of Keystone Species Ecosystem Engineers Keystone Resource Intermediate Disturbance Hypothesis  Disturbance K strategy r strategy Body size Large Small Mortality Low High Onset of maturity Late Early Offspring Few Many Parental care Lots Little  Communities respond to disturbances with stability, which is related to species richness.  Community Resistance & Resilience Ecological trait (e.g., biomass) How much does it change? How long does it take to recover? Time (Hamilton, 2014) Community Stability – Grassland Example Cedar Creek Ecosystem Science Reserve, Minnesota Drought – 1987-1988