Evolution
Tolerance Limits and Species Abundance
tolerance limits- the maximum and minimum levels beyond which a particular species cannot survive or is unable to reproduce, ex. temperatures, moisture levels, nutrient supply, soil and water chemistry, and living space.
-different for each species
-later discovered that rather than a single factor that limited growth, it was several factors working together, that determined biogeographical distribution
-for some species there may be a critical factor that determines their abundance and distribution in an area
-ex. saguaro cactus, sensitive to low temperatures, will begin to die in 12 hours of freezing temps. -young saguaros are more susceptible to cold than adults
-young animals also have more critical tolerance limits than the adults, ex. pupfish
-requirements and tolerances of species often are helpful in understanding the environmental characteristics of an area. the presence of a species can say something about the community and ecosystem
environmental indicators- species with specific tolerance limits that tell us something about the area where they are present ex. locoweeds grow in areas with a high soil concentration of selenium
Natural Selection and Adaptations
-term adapt used in two ways
1. limited range of physiological modifications, called acclimations, available to individual organisms. ex. house plants inside all winter
2. inheritance of specific genetic traits that allow a species to live in a particular environment
evolution- species change gradually through competition for scarce resources and natural selection
natural selection-a process in which those members of a population that are best suited for a particular set of environmental conditions will survive and produce offspring more successfully than their ill-suited competitors
-natural selection acts of preexisting genetic diversity created by small random mutations and occur spontaneously in every population
-mutations alight, but in the long run, create amazing diversity
-theory developed by Charles Darwin
environmental factors that cause selective pressure and influence fertility or survivorship-
1. physiological stresses due to inappropriate levels of some critical environmental factor ex. moisture, light, temp. pH, specific nutrients
2. predation, including parasitism and disease
3. competition
4. luck, sometimes they're just lucky rather than better fir to survive
-selection affects individuals, but evolution and adaptation work at the population level, species evolve not individuals
-isolation can also drive evolution, and cause for variations in species
convergent evolution- when through time when unrelated organisms evolve to look and act very much alike
Niche Specialization
habitat- the place or set of environmental conditions in which a particular organism lives
ecological niche- description of either the role played by a species in a biological community or the total set or environmental factors that determine species distribution
-biophysical definition proposed by G.E. Hutchinson, he said every species has a range of physical and chemical conditions (temp. acidity, humidity etc) as well as biological interactions (predators, prey present, defenses, nutrition available) within which is can exist
-niches can evolve over time
-law of competitive exclusion states that no two species will occupy the same niche and compete for exactly the same resources in the same habitat for very long
resource partitioning- when competition forces one species to either migrate to a new area, become extinct, or change its behavior or physiology in ways that minimize competition
-niche specialization can cause subpopulations of a single species to diverge into separate species, but resources can only be partitioned so far
Species Interactions
Predation
-all organisms need food to live
predator- an organism that feeds directly upon another living organism
-in this broad sense parasites and pathogens may be considered predators
parasites- organisms that feed on a host organism or steal resources from it without killing it
pathogens-disease-causing organisms
-predation is a potent and complex influence on population balance of communities, it involves
1. all stages of the life cycles of predator prey species
2. specialized food obtaining mechanisms
3. specific prey-predator adaptations that either resist or encourage predation
-predation important factor in evolution because predators prey most successfully on the slowest, weakest, least fit members of their target population, causing the prey species to evolve with protective or defensive adaptations to avoid predation
coevolution- the process when predators evolve mechanisms to overcome the evolved defenses of their prey
Keystone Species
keystone species- a species of group of species whose impact on its community or ecosystem is much larger and more influential than would be expected from mere abundance
-many unexpected species can be a keystone species, ex. tropical figs, microorganisms
Competition
-organisms within a community much compete for all the survival necessities: energy and matter in usable forms, space, and specific sites for life activites
intraspecific competition- competition among members of the same species
interspecific competition- competition between members of different species
--competition more of a race than a fight, animals don’t want to risk getting injured
-intraspecific competition intense because organisms are fighting directly for the exact same resources
territoriality- intense form of intraspecific competition in which organisms define an area surrounding their home site or nesting site and defend it, primarily against other members of their own species
-territorilaity helps to allocate resources by spacing members of a species
Symbiosis-intimate living together of members or two or more species
Mutualism- a type of symbiosis in which both members of the partnership benefit.
ex. lichens being a combination of fungus and a photosynthetic partner, alga or cyanobacterium
-mutualistic relationship may be important in evolution
Commensalism- a type of symbiosis in which one member clearly benefits and the other apparently is neither benefited nor harmed
ex. cattle and cattle egrets
Parasitism-a form of symbiosis in which one species benefits and the other is harmed.
ex. Ms. Law and tropical round worms
Defensive Mechanisms-the way that different prey adapt to either hide from or discourage predators
ex. toxic chemicals, body armor
-some organisms produce noxious odors or poisonous secretions
-plants too produce chemical compounds that make them unpalapable or dangerous to disturb
ex. poison ivy, stinging nettles
Batesian mimicry- harmless species that evolve colors, patterns, or body shapes that mimic species that are unpalpable or poisonous
Mullerian Mimicry- when two dangerous species evolve to look alike
-others use camouflage
Community Properties
-productivity, diversity, complexity, resilience, stability, and structure
Productivity-
primary productivity- rate of biomass production
-higher productivity in areas of high temperature moisture and nutrient availability
Abundance and Diversity-
abundance-expression of the total number of organisms in a biological community
diversity- measure of the number of different species, ecological niches, or genetic variation present
-as you go from the equator towards the poles, generally diversity decreases but abundance increases
-productivity is related to abundance and diversity
Complexity and Connectedness
complexity-refers to the number of species at each trophic level and the number of trophic levels in a community
-you can have an abundant community that isn't very complex
Ecological Succession-
-the process by which organisms occupy a site and gradually change environmental conditions b creating soil, shade, shelter, or increasing humidity
Primary Succession-occurs when a community begins to develop on a site previously unoccupied by living organisms
ex. island, new volcanic flow
pioneer species- in primary succession, the species that fist colonizes the new area
-often microbes, mosses and lichens
ecological development- process or environmental modification by organisms
Secondary Succession-occurs when an existing community is disrupted and a new one subsequently develops at the site
-disruption may be caused by natural catastrophe, human activity
climax community- in either primary or secondary succession, when a community develops that resists further change
equilibrium communities/disclimax communities- when landscapes never reach a stable climax in the traditional sense because they are characterized by periodic disruption
Aquatic Succession-process or succession taking place in a body or water
