Chapter 54: Community Ecology

Chapter 54: Community Ecology 54.1 Interactions between species can help, harm, or have no effect on the individuals involved Community: A group of populations of different species that live in close enough proximity to interact with one another Interspecies interactions: A relationship between individuals of two or more species in a community There are many different types of interactions ( represented a + positive, - negative, or 0 neutral for one species / +,-,0 for the other):         (+/-) Predation o An interaction by which one species kills and eats on individuals of another species o Can happen on the micro and macro level o Forces evolution and natural selection for both the predator and the prey and leads to various adaptations (+/+) Mutualism o An interaction in which both species help each other with costs and benefits of survival (-/-) Competition o Occurs when individuals of different species each use a resource that limits the survival and reproduction of both individuals and can even occur among those in the same species o Can lead to competitive exclusion: the idea that when two similar species compete for the same resource, one will one that will obtain and use it more efficiently than the other and lead to an advantage that can cause the other species to die out  This can be averted, and the species can coexist if changes in their niches happen over time  This can lead to resource portioning: The changes in niches that allows similar species to coexist in a community (+/-) Exploitation o An interaction in which one species benefits by feeding on an individual of another species (+/+ or +/0) Positive interactions (+/-) Herbivory o When an herbivore eats parts or all a plant or algae and harms it but does not kill it o Also leads to natural selection and evolution  Herbivores learn to distinguish good plants and harmful or poisonous ones  Plants over time develop physical defense such as spines or thorns or chemical defenses (+/-) Parasitism o When a parasite derives nutrients or shelter at the expense of the host  2 types Ectoparasites: Ectoparasites (outside the body) or Endoparasites (inside the body) o Parasites can lead to decreased survival and reproduction in their host’s population (+/0) Commensalism o An interaction in which one species gets benefits and the other one is not harmed nor helped Ecological niche: the specific set of biotic and abiotic resources that an organism uses in its environment. It can also be called an organism’s role in the environment and through studying niches, we can understand how populations change over time Character displacement: the tendency for characteristics to be more diverse in sympatric populations of two species than in allopatric populations of the same two species Various adaptations used in response to predation:    Aposematic coloration: It is a warning coloration that is bright and showy and is a sign of chemical defenses such as bad taste, poisons, etc. Cryptic coloration: Also known as camouflage that makes individuals harder to spot. o It is used by both predator and prey Mimicry is also employed as a defense against predation: o Batesian mimicry: This happens when a harmless species mimics the coloration or body shape of species that are harmful or unpalatable to predators o Mullerian mimicry: This happens when two or more unpalatable species look like one another  It is a form of mutualism in a weird way.  The way to remember this one is that mutualism and Mullerian both start with M 54.2 Diversity of the trophic structure characterize Ecological communities Species Diversity: The variety of different kinds of organisms that make up a ecological community This is measure by two measurements:   Species richness: The number of different species in the community Relative abundance: The proportion each species represents of all the individuals in the community Sometimes hard to tell with microbes and requires using molecular diagnostics to discover Diverse communities are better able to handle stress and end up producing more biomass than less diverse communities. They also handle invasive species better. Trophic structure: The different feeding relationships in an ecosystem which determine the route of energy flow and pattern of chemical cycling Food Chain: The pathway in which food energy is transferred from a trophic level (the level an organism occupies) to the next level, starting from producers Food webs link multiple chains together sharing other possible feeding relationships and organisms may weave in at different trophic levels. Food webs can be simplified down for simpler study Food chains only have five or four links which is by the energetic hypothesis which suggests that the food chain is limited by inefficient energy transfer along the chain as countermeasures for being large at higher levels. Foundation species: a species that has a strong effect on their communities by having a large, abundant, or pivotal role. May provide food, habitat, or be competitively dominant. They can be found if removed from the environment. Keystone species: A species that is not usually abundant in an ecosystem but hold a pivotal role their communities Ecosystem engineers: A species that influences the community by changing an environment or creating a new one Bottom-up control: The abundance of organisms at each trophic level is limited by the nutrient supply or availability of food at a lower trophic level. Top-down control: The abundance of organisms at each level is controlled by the abundance of consumers at higher levels 54.3 Disturbances influences species diversity and composition Stability: the idea that a community tends to reach and maintain a relatively constant composition of species Some argued that a climax community was the end goal and was regulated by climate but as people analyzed that, they found that was not the case Many disturbances keep things like the community from reaching equilibrium, leading to the nonequilibrium model which states that most communities are constantly changing after a disturbance. The Intermediate-disturbance hypothesis: The idea that moderate levels of disturbances foster greater species diversity than great or low disturbances. But small and high disturbances have important impacts on community structures such as creating patches of different environments or helping the cycle of life move along Two types of succession after a disturbance:   Primary succession: Ecological succession that happens in areas where no organisms were present, or no soil was formed Secondary succession: the recolonization of an area after a disturbance that removed most but not all organisms in a community 54.4 Biogeographic factors affect community diversity The tropics has the most diversity because they have had fewer disturbances than other latitudes and that has allowed for greater speciation Climate also has had an effect mainly because of sunlight and precipitation which are measured by evapotranspiration: the evaporation of water from soil and plants and that positively correlates with species richness Species-Area curve: All other factors being equal the larger the area for a community than the more species that are in it and the greater the diversity Islands are great for studying species diversity and factors that affect it Islands show an equilibrium model in which equilibrium is reached when rate of immigration of populations = rate of extinction in these islands. 54.5 Pathogens alter community structures locally and globally Pathogens have very strong effect when introduced into communities and can drastically reduce them This is especially evident in human communities ¾ of all current diseases of concern are caused by zoonotic pathogens: pathogens that jumped to humans from animals, which are used as a vector. The key to limiting the outbreaks is by finding the host and the pathogen itself Human impact of the environment can increase the rates of these infections:    Many wild animals are colonizing new places Humans and wild animals are closer than in the past due to urbanization Humans can transfer these diseases quickly around the globe before detection can take place.