Community Ecology: Structure, Species Interactions, Succession, and Sustainability G. Tyler Miller ’ s Living in the Environment 13 th Edition Chapter 8 G. Tyler Miller ’ s Living in the Environment 13 th Edition Chapter 8 Dr. Richard Clements Chattanooga State Technical Community College Modified by Charlotte Kirkpatrick Dr. Richard Clements Chattanooga State Technical Community College Modified by Charlotte Kirkpatrick

Key Concepts  Community structure  Roles of species  Species interactions  Changes in ecosystems  Stability of ecosystems

Community Structure (Spatial Distribution): Four Characteristics  Physical Appearance: Stratification, relative sizes and distribution of its population and species  Species diversity (richness): Number of different species in a community  Species abundance: Number of individuals of each species  Niche structure: number of ecological niches, how they resemble or differ from each other and how they interact (species interactions)

Community Structure: Appearance and Species Diversity Fig. 8-2 p. 166 The types, relative sizes, and stratification of plant species in various terrestrial communities or ecosystems (also seen in aquatic systems)

Physical Structures Physical structure within an ecosystem or community can vary. Usually see large vegetative patches (mosaic) of differing size in large ecosystems or communities. Leads to sharp edges as seen in forest and open field or wider more diverse ecotones. Result of the differences in physical structure and properties at ecotones can lead to an edge effect.

Biodiversity: factors that affect species diversity  Latitude: diversity decreases with increase in latitude  Depth: diversity increase with depth to 2000m and decreases until the sea bottom where species diversity is high Fig. 8-3 and 8-4 p. 167 Ants Birds

Biodiversity: factors that affect species diversity Pollution: in aquatic systems diversity decreases with increase in pollution. Terrestrial ecosystems: diversity tends to increase with increasing solar radiation, increasing precipitation, decreasing elevation, and pronounced seasonal variations Unpolluted stream Polluted stream Number of diatom species Number of individuals per diatom species

Island Diversity Two factors effect isolated ecosystem (such as an island) diversity: size and degree of isolation (distance from mainland) –Theory of Island Biogeography by Robert MacArthur, Edward O. Wilson: balance between two factors »The rate at which new species immigrate and the rate at which species become extinct on the island

Theory of Island Biogeography Also see fig. 8-7 pg. 169

General Types of Species  Native: species that normally live in and thrive in a particular ecosystem  Non-native (exotic or alien): organisms that migrate into an ecosystem or are accidentally or deliberately introduced into an ecosystem Zebra mussel pageZebra mussel page  Non-native (exotic or alien): organisms that migrate into an ecosystem or are accidentally or deliberately introduced into an ecosystem Zebra mussel pageZebra mussel page  Indicator: Species that serve as early warnings of damage to a community or an ecosystem. Amphibians ( see connections p )

General Types of Species (cont.)  Keystone: role in ecosystem of species which is actually more influential than numbers or biomass suggests.  These organism play a pivotal role in the structure and function of ecosystem because they have strong interaction with other species that affect their health and survival, and process material out of proportion to their numbers or biomass.  Critical roles: pollination, dispersion of seeds, habitat modification, predation, improve ability of plants to absorb nutrients and water, and efficient recycling.  Loss of keystone species can lead to population crashes and extinctions of other species i.e. domino effect.  Keystone: role in ecosystem of species which is actually more influential than numbers or biomass suggests.  These organism play a pivotal role in the structure and function of ecosystem because they have strong interaction with other species that affect their health and survival, and process material out of proportion to their numbers or biomass.  Critical roles: pollination, dispersion of seeds, habitat modification, predation, improve ability of plants to absorb nutrients and water, and efficient recycling.  Loss of keystone species can lead to population crashes and extinctions of other species i.e. domino effect.

Species Interactions: Competition  Intraspecific competition: within a species for resources and territoriality.  Interspecific competition: between different species for limited resources (niche overlap)  Competing species must:  Migrate to another area  Shift its feeding habits or behavior through evolution and natural selection  Suffer a sharp decline in population  Extinction  Interspecific competition: between different species for limited resources (niche overlap)  Competing species must:  Migrate to another area  Shift its feeding habits or behavior through evolution and natural selection  Suffer a sharp decline in population  Extinction

Species Interactions: Competition  Interference competition: one species influences another ’ s access to some resource regardless of its abundance. Ex. hummingbird  Exploitation competition: Two competing species have roughly equal access but differ in how fast or efficiently they exploit it.

Species Interactions: Competition  Competitive exclusion principle: by Gauss describes how one species eliminates another in an area through competition for limited resources.

Resource Partitioning Fig. 8-9 p. 175; Refer to Fig p. 152 & Fig p. 175  Resource partitioning: a method to reduce competition, dividing up the resource so that species with similar needs use them at different times, in different ways, or in different places.

Species Interactions: Predation  Predator: feeds directly on all or part of a living organism  Prey: organism fed on.  Prey acquisition: herbivores vs. carnivores (pursue or ambush)  Predator Avoidance: speed, highly developed senses,protective coverings  Predator-prey relationship: One organism is clearly harmed. However at the population level there are benefits: improve access to food, and improve the genetic stock.

Predator Avoidance by Prey camouflage Chemical warfare Warning coloration mimicry Deceptive looks Deceptive behavior

Symbiotic Relationships Symbiosis is a relationship in which species live together in an intimate association. There are three types: –Parasitism (special form of predation) –Mutualism –Commensalism

Symbiotic Species Interactions: Parasitism  Parasite: organisms that feeds on another by living in or on another living organism. Parasite benefits.  Host: Organism that a parasite feeds on and lives in or on. Host is harmed. (rarely killed)  Endoparasites: parasites found inside the host organisms body. Ex.tapeworms,disease causing microorganisms.  Ectoparasites: organisms found outside the host organisms body. Ex. Fleas, ticks, mosquitoes

Symbiotic Species Interactions: Mutualism  Reproductive mutualism: pollination  Nutritional mutualism  Nutritional/protection mutualism Fig p. 179

Symbiotic Species Interactions: Commensalism  Indirect: i.e., small plants growing in shade of larger plants (redwood sorrel)  Direct: i.e., epiphytes (orchids and bromeliads), remoras Fig p. 180

Ecological Succession: Communities in Transition  Primary succession  Secondary succession  Pioneer species  Successional species

Primary Succession Fig p. 180

Secondary Succession Fig p. 181

Succession and Wildlife Fig p. 182

The Rate of Succession Refer to Table 8-1 p. 182  Facilitation: one set of species makes an area suitable for species with different nich requirements.  Inhibition: early species hinder the establishment and growth of other species. Inhibiting species must be removed for succession to continue  Tolerance: late successional species are largely unaffected by plants at earlier stages of succession

Ecological Stability and Sustainability Refer to Table 8-2 p. 193  Disturbance: can be catastrophic or gradual; human caused or natural. May convert a particular stage of succession to an earlier one.  Climax community: end product of succession; stable and predictable community dominated by a few long-loved plant species and in balance with its environment. Known as balance of nature.  This is not actually the case due to several unpredictable small and medium-sized disturbances.  Climax community: end product of succession; stable and predictable community dominated by a few long-loved plant species and in balance with its environment. Known as balance of nature.  This is not actually the case due to several unpredictable small and medium-sized disturbances.

Ecological Stability and Sustainability  Inertia (or persistence): ability of a living system to resist being disturbed or altered.  Constancy: the ability of a living system such as as population to keep its numbers within the limits imposed by available resources.  Resilience: the ability of a living system to bounce back after an external or internal disturbance that is not too drastic.  Precautionary principle

Species Diversity and Ecosystem Stability Many believe that the more diverse the ecosystem the more stable. This is not completely supported. And is difficult to determine Generally we find that the more species diversity has higher net primary productivity, and more resilient, yet population of individual species can fluctuate. Some level of biodiversity is needed in various ecosystem to provide insurance against catastrophe. Yet, how much biodiversity is needed for this stability.

Species Diversity and Ecosystem Stability Many ecologists disagree on how to define stability and diversity. Does an ecosystem need both inertia and high resilience to be stable? Ex. Rain forests vs. grasslands. Another difficulty is that populations, communities, and ecosystems are rarely if ever at equilibrium. Instead nature is in a continuing state of disturbance, fluctuation, and change

Precautionary Principle Why should we protect our natural systems and biodiversity if it doesn ’ t lead to increased stability and if nature is mostly unpredictable? Precautionary principle: when evidence indicates that an activity can harm human health or the environment, we should take precautionary measures to prevent harm even if some of the cause and effect relationships have not been fully established scientifically.