Communities and Ecosystems A study of how biotic and abiotic factors influence communities.
abiotic factors physical aspects i.e. soil, water, weather (non-living) biotic factors the Organisms Food supply Vectors Demographic events (living) A dynamic system of species that form a community TOGETHER WITH their physical environment.
Abiotic: Climate & Weather What is climate, and how does it differ from weather? How do climate and weather affect organisms and ecosystems?
Weather and Climate Weather is the day-to-day condition of Earth s atmosphere.
Weather and Climate Climate refers to average conditions over long periods and is defined by year-after-year patterns of temperature and precipitation. Climate is rarely uniform even within a region. Environmental conditions can vary over small distances, creating microclimates. For example, in the Northern Hemisphere, southfacing sides of trees and buildings receive more sunlight, and are often warmer and drier, than northfacing sides. These differences can be very important to organisms in an ecosystem.
Solar Energy and the Greenhouse Effect The main force that shapes our climate is solar energy that arrives as sunlight that strikes Earth s surface. Some of that energy is reflected back into space, and some is absorbed and converted into heat.
Some of the heat also radiates back into space, and some is trapped in the biosphere. The balance between heat that stays in the biosphere and heat lost to space determines Earth s average temperature.
Earth s temperature is largely controlled by concentrations of three atmospheric gases carbon dioxide, methane, and water vapor. These greenhouse gases function like glass in a greenhouse, allowing visible light to enter but trapping heat through a phenomenon called the greenhouse effect.
If greenhouse gas concentrations rise, they trap more heat, so Earth warms. If their concentrations fall, more heat escapes, and Earth cools. Without the greenhouse effect, Earth would be about 30 C cooler than it is today.
Latitude and Solar Energy Near the equator, solar energy is intense, as the sun is almost directly overhead at noon all year. That s why equatorial regions are generally so warm. The curvature of Earth causes the same amount of solar energy to spread out over a much larger area near the poles than near the equator.
Earth s polar areas annually receive less intense solar energy, and therefore heat, from the sun. The difference in heat distribution creates three different climate zones: tropical, temperate, and polar.
Climate determines what plants will grow, which determines how many and what type of animals can be supported. Climate determines what adaptations organisms need to survive and reproduce.
If you ask someone where an organism lives, that person might answer on a coral reef or in the desert. These answers give the environment or location, but ecologists need more information to understand fully why an organism lives where it does and how it fits into its surroundings. What else do they need to know?
When we study ecosystems we define them by their biotic and abiotic factors.
We can construct Food Webs to show matter and energy flow
But to better understand all the interactions within the ecosystem, We identify the RELATIONSHIPS between the populations that live there.
To understand relationships, we study the particular NICHE of any population in the ecosystem No two species occupy the same niche in a community/ habitat
A niche is the range of physical and biological conditions in which a species lives and the way the species obtains what it needs to survive and reproduce.
In other words An organism s niche describes not only the environment where it lives, but how it interacts with biotic and abiotic factors in the environment. It s niche includes the way in which the organism uses the physical and biological aspect of its environment to survive and reproduce.
Resources and the Niche The term resource can refer to any necessity of life, such as water, nutrients, light, food, or space.
Resources For plants, resources can include sunlight, water, and soil nutrients. For animals, resources can include nesting space, shelter, types of food, and places to feed.
Physical Aspects of the Niche Part of an organism s niche involves the abiotic factors it requires for survival. Most amphibians, for example, lose and absorb water through their skin, so they must live in moist places. If an area is too hot and dry, or too cold for too long, most amphibians cannot survive. frogsicles
Biological Aspects of the Niche Biological aspects of an organism s niche involve the biotic factors it requires for survival, such as when and how it reproduces, the food it eats, and the way in which it obtains that food. Birds on Christmas Island in the Indian Ocean, for example, all live in the same habitat but they prey on fish of different sizes, nest at different times of year and feed in different places. Thus, each species occupies a distinct niche
Tolerance Every species has its own range of tolerance, the ability to survive and reproduce under a range of environmental circumstances.
When an environmental condition, such as temperature, extends in either direction beyond an organism s optimum range, the organism experiences stress. The organism must expend more energy to maintain homeostasis, and so has less energy left for growth and reproduction.
Organisms have an upper and lower limit of tolerance for every environmental factor. Beyond those limits, the organism cannot survive. A species tolerance for environmental conditions, then, helps determine its habitat (the general place where an organism lives) and its niche.
Some ecosystems present extreme conditions under which organisms must adapt to live there. Even in extreme environments, however, an organism s niche can be affected if conditions push the limits of it s tolerance.
Hatch a Cyst Abuse a Cyst Affecting an organism s niche
What do these two animals have in common?
Arthropods - An arthropod is an invertebrate animal having an exoskeleton, a segmented body, and jointed appendages. Arthropods include the insects, arachnids, myriapods, and crustaceans. They make up over threefourths of all currently known living and fossil organisms. Because their skeletons are on the outside, they have to shed them as they grow.
Hatch-a-Cyst the habitat (the Great Salt Lake)
Hatch-a-Cyst the Great Salt Lake Great Salt Lake has a much greater surface-areato-volume ratio than other lakes in the region. As a result, a tremendous amount of water -- an average of 2.6 billion gallons -- evaporates from the lake each day. This affects not only the lake's depth, but also the weather. Moisture from the lake produces lake effect snow during the winter, and afternoon thunderstorms during the summer.
Hatch-a-Cyst the Great Salt Lake Great Salt Lake sits at the bottom of a "closed basin". It's a terminal lake. The only way water can leave is through evaporation. So what goes into the lake tends to stay in the lake. Most terminal lakes have a high mineral content and are quite salty. Even though the water flowing into Great Salt Lake is fresh, it contains small amounts of dissolved minerals. As water evaporates from the lake, the minerals stay behind. Over many thousands of years, minerals have accumulated to very high levels.
Hatch-a-Cyst the Great Salt Lake Salinity Great Salt Lake is between 3.5 and 8 times saltier than the ocean. The organisms that live in the water have special adaptations that allow them to survive such saline conditions.
Great Salt Lake food web The Great Salt Lake food web is relatively simple. It is based around two major food chains. The first food chain (on the left side of the diagram) consists of microscopic bottomdwelling cyanobacteria, brine flies and shorebirds such as gulls. The second food chain (on the right) is made up of the free-floating algae Dunaliella, brine shrimp and waterbirds such as Eared grebes.
Energy transfer in the ecosystem Remember energy is lost at each level of the food chain, the biomass at each level decreases as you go up. That is, the total mass of all the producers is greater than the mass of the primary consumers, which is greater than the mass of the secondary consumers, and so on. The difference in biomass reflects the amount of energy lost at each level.
Hatch-a-Cyst Brine shrimp (genus Artemia) are an aquatic crustacean. They are not marine but grow in brackish fresh water lakes like Great Salt Lake. At a maximum length of just over 1 cm (0.4 inch), brine shrimp are the largest animals that live in Great Salt Lake. Despite their small size, they are an important part of the lake's ecosystem. Each year millions of birds fatten up on brine shrimp as they prepare nest or migrate around the globe.
Hatch-a-Cyst Brine shrimp life cycle
Abuse-a-Cyst When conditions in Great Salt Lake become especially hostile, Artemia can produce dormant eggs, known as cysts. Dormant brine shrimp embryos can remain protected inside cysts until conditions improve. The resilience of Artemia makes them ideal animals for running biological toxicity assays and it has become a model organism used to test the toxicity of certain chemicals.
Species interactions in Communities
competition 2 species use the same resource in a habitat
competition All organisms in any ecosystem have some effect on every other organism in that ecosystem. Any resource in any ecosystem exists only in a limited supply. When these two conditions apply jointly, competition takes place.
an interaction between individuals brought about by a shared requirement for a resource in limited supply, leading to a reduction in survivorship, growth, and/or reproduction of the individuals concerned.
How might a population s niche be affected by competition?
By causing species to divide resources, competition helps determine the number and kinds of species in a community and the niche each species occupies. The amount of competition depends on how much each species need from the resource overlaps.
When organisms compete, one of two outcomes: Share the resource (resource partitioning) One wins, one loses Competitive exclusion principle The trade off is the reduction in population size; or change of habits The losing population can no longer live there
Resource partitioning
Resource partitioning example The resources utilized by these species are similar yet different. Therefore, each species has its own niche and competition is minimized.
Resource sharing (partitioning) For example: In a woodland, species compete for light. Trees can outcompete smaller plants. In a deciduous woodland, flowers such as snowdrops and bluebells carry out their life cycle during times when the trees have no/few leaves.
Realized niche
The Competitive Exclusion Principle The competitive exclusion principle states that no two species can occupy exactly the same niche in exactly the same habitat at exactly the same time. If two species attempt to occupy the same niche, one species will be better at competing for limited resources and will eventually exclude the other species..
The Competitive Exclusion Principle In the the experiment shown in the graph, two species of paramecia (P. aurelia and P. caudatum) were first grown in separate cultures (dashed lines). In separate cultures, but under the same conditions, both populations grew. However, when both species were grown together in the same culture (solid line), one species outcompeted the other, and the less competitive species did not survive.
Predation How does predation shape communities?
Predator-Prey Relationships An interaction in which one animal (the How would you define this predator) captures and feeds on another animal (the prey) is called predation. symbiotic relationship? Predators can affect the size of prey populations in a community and determine the places prey can live and feed.
Birds of prey, for example, can play an important role in regulating the population sizes of mice, voles, and other small mammals.
This relationship creates a predictable pattern.
The extinction of one species in an ecosystem can have an impact on all other species.
Energy and matter flow through an ecosystem depends on the communities of organisms and their niches.
When we consider the flow of E and matter through an ecosystem keystone species
Keystone Species A keystone species has a disproportionately large effect on its environment relative to its abundance. Keystone species play a critical role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem and helping to determine the types and numbers of various other species in the community.
The role that a keystone species plays in its ecosystem is analogous to the role of a keystone in an arch. While the keystone is under the least pressure of any of the stones in an arch, the arch still collapses without it. Similarly, an ecosystem may experience a dramatic shift if a keystone species is removed, even though that species was a small part of the ecosystem by measures of biomass or productivity.
Washington intertidal food web a keystone predator is one of high trophic status. Through its feeding activities it exerts a disproportionate influence on community structure.
Visualise a classic feeding pyramid, where a top predator eats another predator and this predator eats an herbivore, and so on. Removal of the top predator can cause repercussions throughout the ecosystem. The importance of a keystone predator is most evident when its principal prey is a species that monopolizes a basic resource, such as space, and out-competes or excludes other species. The sea stars attack from lower in the intertidal zone, moving up when the tide comes in and wrenching the mussels free from their attachment. They then crawl downwards with their prey to digest them. The sea stars effectively set the lower limits of distribution of the mussels. Note the dominance of mussels in the higher zone, and their replacement by algae in the lower zone
A textbook example: Dr. Robert Paine, 1974 Oecologia 15: 93.
Mukkaw Bay, Washington Pisaster ochraceus When Pisaster was removed from an intertidal zone, mussels eventually took over the ecosystem, eliminating most other invertebrates and algae.
Another Keystone Species example Changes in the population of a keystone species, can cause dramatic changes in the structure of a community. In the cold waters off the Pacific coast of North America, for example, sea otters devour large quantities of sea urchins. Urchins are herbivores whose favorite food is kelp, giant algae that grow in undersea forests.
A century ago, sea otters were nearly eliminated by hunting. Unexpectedly, the kelp forest nearly vanished. Without otters as predators, the sea urchin population skyrocketed, and armies of urchins devoured kelp down to bare rock.
Without kelp to provide habitat, many other animals, including seabirds, disappeared. Otters were a keystone species in this community.
After otters were protected as an endangered species, their population began to recover. As otters returned, the urchin populations dropped, and kelp forests began to thrive again. Recently, however, the otter population has been falling again, and no one knows why.
Keystone species and dominant vegetation together delineate a specific ecosystem or on a grand scale a BIOME