BIOL227 Discussion 11 - Ecological Biodiversity PDF

Community Ecology  The biosphere Organelles 1 µm Ecosystems Cell Cells...

Community Ecology  The biosphere Organelles 1 µm Ecosystems Cell Cells Atoms Molecules 10 µm Communities Tissues 50 µm Populations Organs and organ systems Organisms Species Diversity Species diversity of a community is the variety of organisms that make up the community It has two components: 1. Species Richness Species richness is the total number of different species in the community 2. Relative Abundance Relative abundance is the proportion each species represents of the total individuals in the community Richness versus Abundance Two communities can have the same species richness but a different relative abundance A community with an even species abundance is more diverse than one in which one or two species are abundant and the remainder are rare The basis for understanding community ecology: Ecological interactions Interspecific vs. Intraspecific Interactions Interspecific Interactions Ecologists call relationships between species in a community interspecific interactions For example, two species engage in interspecific competition for a limiting resource, the result is detrimental to one or both species (−/−). Interspecific interactions affect species survival and reproduction Examples are competition, predation, herbivory, symbiosis (parasitism, mutualism, and commensalism), and disease Interspecific Interactions Can have differing effects on the populations involved Competition (-/-) Interspecific competition Occurs when different species compete for a particular resource that is in short supply Strong competition can lead to competitive exclusion The local elimination of one of the two competing species Competitive Exclusion The ecological niche is the total of an organism’s use of the biotic and abiotic resources in its environment The competitive exclusion principle (Gause’s Law) states that two species competing for the same limiting resources cannot coexist in the same place Can lead to the local elimination of one of the two competing species, a process called competitive exclusion. Coexistence occurs when overlap between niches is reduced Experimental Evidence Ecological Niche The total requirements of a species for all resources and physical conditions determine where it can live and how abundant it can be at any one place within its range. The ecological niche of an organism depends not only on where it lives but also on what it does. Ecological Niche Fundamental niche Potential ecological niche for an organism The fundamental niche is the niche that an organism would occupy in the absence of competition Realized niche Niche an organism actually occupies niche that an organism occupies in the presence of competition Resource Partitioning When competition between two species with identical niches does not lead to the local extinction of either species It is generally because evolution by natural selection has resulted in the modification of the resources used by one of the species. Resource partitioning is the differentiation of niches that enables two similar species to coexist in a community. Character Displacement Character displacement is the tendency for characteristics to be more divergent in sympatric populations of two species Competing species evolve slightly different niches to avoid competition Reduces Interspecific Competition An example is variation in beak size between populations of two species of Galapagos finches Predation (+/-) Refers to an interaction where one species, the predator, kills and eats the other, the prey (+/– interaction) Feeding adaptations of predators include: Claws, teeth, fangs, stingers, and poison Natural selection shapes the body forms and behaviors of both predators and prey Prey Strategies Prey animals have evolved adaptations that help them avoid being eaten. Behavioral defenses include fleeing, hiding, and self-defense. Alarm calls may summon many individuals of the prey species to mob the predator. Cryptic coloration, or camouflage - makes prey difficult to spot Aposematic coloration: Warns predators to stay away from prey Aposematic coloration Cryptic coloration  In some cases, one prey species may gain significant protection by mimicking the Batesian Mimircy appearance of another In Batesian mimicry A palatable or harmless species mimics an unpalatable or harmful model A Batesian mimic is a sheep in wolf's clothing.  Müllerian Mimicry Two or more species resemble each other The animal mimics the attributes of a poisonous creature, when it actually is itself is unpalatable Predators will quickly adapt by avoiding this particular appearance Herbivory (+/-) Herbivory, the process in which an herbivore eats parts of a plant (+/–) Has led to the evolution of plant mechanical (spines, tough leaves) and chemical defenses and consequent adaptations by herbivores Milkweeds produce chemicals that are poisonous to all but a few insects Symbiosis Any intimate or long-term association between two or more species Symbiosis is always ‘inter-specific’; that is it occurs only between different species Two main types of Symbiosis 1. Parasitism (+/-) 2. Facilitation Facilitation is when one organism benefits and the other is unaffected or benefits as well (MUTUALISM OR COMMENSALISM 1) Parasitism In parasitism (+/-), one organism, the parasite derives its nourishment from another organism, its host, which is harmed in the process Endoparasites live within the body of the host Ectoparasites live and feed on the external surface of the host. Mites living in the trachea of honeybees Clog airways which eventually kills them Fruitbody of the fungus, growing out of an infected ant that clings itself to a tree 2) Commensalism (+/0) One species benefits and the other is not significantly affected Who benefits?  One species benefits and the other is not affected (in any known way) These interactions hard to document… An epiphyte is a plant that normally grows on another plant for support. It is not parasitic but uses the host plant for support Clownfishes & sea only. anemones. 3) Mutualism Mutualistic symbiosis, or mutualism (+/+), is an interspecific interaction that benefits both species A mutualism can be Obligate, where one species cannot survive without the other Facultative, where both species can survive alone  Rhizobium & legume plants Coral: zooxanthallae & polyp Humans & microbes Mycorrhizae: plant & fungus Alga provides fungi with food (“fixed” organic carbon) & fungi provide alga /cyanobacteria with minerals, water, shelter, secrete chemicals which ward off predators and repel microbes. fungal hyphae Lichen structure: algae (or cyanobacteria) Species with a Large Impact: Dominant Species Dominant species are those that are most abundant or have the highest biomass They exert powerful control over the occurrence and distribution of other species Example: the sugar maple that dominates the North American forest Dense and high tree canopy reduces the light for species living on the ground Species with a Large Impact: Invasive Species Invasive species, typically introduced to a new environment by humans, often lack predators or disease Species with a Large Impact: Keystone Species Species with a Large Impact: Foundation Species (ecosystem engineers) Ecosystems Two Concepts About Ecosystems 1. Energy flow thru ecosystems (refer back to lecture 2) 2. Cycling of chemical elements in ecosystems  Primary Production in an Ecosystem Primary production is the amount of light energy converted to chemical energy by autotrophs during a given time period The extent of photosynthetic production sets the spending limit for the energy budget of the entire ecosystem The amount of solar radiation reaching the surface of the Earth limits the photosynthetic output of ecosystems  Food Webs In real life, food chains are not this simple as several different, but interrelated (connected) food chains combine together into a food web. At the next level, carnivores also tend to eat a number of different prey This results in an interconnected food web Food webs describe the movement of energy from one species to another in the community Nutrient Cycles in The Ecosystem Nitrogen Cycle Carbon Cycle Water Cycle The Phosphorus Cycle Threats to Biodiversity Species Diversity Endangerment