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AP Environmental Science Community Processes: Species Interactions and Succession © Brooks/Cole Publishing Company / ITP 1. The Ecological Niche Niche- the role that an organism plays in an ecosystem. • Defined by the range of conditions and resources within which an organism can live • Conditions- physical attributes of the environment, though not consumed, that influence biological processes and population growth, e.g., temperature, salinity, acidity • Resources- substances or parts of the environment used and consumed or otherwise made unavailable to other organisms, e.g., food, water, and nesting sites for animals; water, nutrients, and solar radiation for plants; Contrast with habitat, the actual place an organism lives. © Brooks/Cole Publishing Company / ITP Generalists vs. Specialists Generalists- have broad niches, whereas Specialists- have narrow niches: Generalists: • Cockroaches, coyotes, dandelions, humans • Have advantage when environmental conditions change • Eat wide variety of food and tolerate wide range of conditions: VERY ADAPTABLE Specialists: • Spotted owls require old–growth forests, giant pandas eat primarily bamboo in bamboo forests of China • Have advantage when environmental conditions are more constant. Prone to © Brooks/Cole Publishing Company / ITP Fundamental vs. Realized Niche Fundamental niche- full range of conditions and resources that an organism could theoretically use in the absence of competition with other species. Realized niche- portion of the fundamental niche that an organism actually occupies; actual range of conditions and resources that an organism uses. • Niche overlap between species leads to competition © Brooks/Cole Publishing Company / ITP Community Three characteristics to describe a biological community – 1. Physical appearance Size, stratification, and distribution Transitional edges between communities can cause variance of community—increased edge area = increased vulnerability – 2. Species diversity Combination of # of different species (richness) and the # of individuals within each species (evenness) Affected by latitude, pollution, habitat diversity, NPP, etc. Tropical rainforest at equator (low latitude) most diverse – 3. Niche structure The number of niches and variety and species interaction with one another 2. Some General Types of Species Native species- species that normally live and thrive in a particular ecosystem: • Nonnative species (also called exotic species or alien species)- originate in other ecosystems •May enter an ecosystem by migration or by deliberate or accidental introduction by humans •Example: "killer bees", wild bees from Africa were imported to Brazil to increase honey production, but displaced native bees, decreased honey production, spread. •Newly arrived nonnative species usually not able to survive, but when they take hold they © Brooks/Cole Publishing Company / ITP can be invasive. Some General Types of Species Indicator species- species that serve as early warnings that a community or ecosystem is being damaged: • Example: decline of migratory songbirds in North America indicates loss and fragmentation of habitat in meso-America and South America • Example: presence of trout in mountain streams is an indicator of good water quality • Example: spotted owls are indicator of healthy old–growth forest. • Example: amphibians are especially vulnerable to environmental disruption at several stages in their lives © Brooks/Cole Publishing Company / ITP Adult frog (3 years) Figure 8-6 Page 147 sperm Young frog Tadpole develops Into frog Sexual reproduction Tadpole Eggs Fertilized egg development Egg hatches Organ formation Some General Types of Species Keystone species- species that play a critical role in an ecosystem • Example: sea otters because they prevent sea urchins from depleting kelp beds • Example: dung beetles because they remove, bury and recycle animal waste • Example: beavers are because they build dams and create habitat for a diverse community of species (bluegill fish, muskrats, herons, ducks…). © Brooks/Cole Publishing Company / ITP Some General Types of Species Foundation species- can create and enhance habitats that can benefit other species in a community Elephants in the savannas uprooting trees benefits growing grasses, smaller grazing species, accelerates nutrient cycling Bats and birds can distribute seeds in waste, regenerating deforested areas. 3. Types of Species Interactions Major types of biotic interactions: • Interspecific competition- 2 or more species use same limited resources so fundamental niche overlap. Example: fire ants are better competitors than native species of North America and sharply reduce their populations up to 90% Example: humans and many other species • Resource partitioning- species competing for similar scarce resources evolve more specialized traits that allow them to use shared resources at different times, in different ways, or in different places © Brooks/Cole Publishing Company / ITP Resource Partitioning Species with similar resource needs can coexist because they use limited resources at different times, in different ways, or in different places. • Example, specialized feeding niches of various birds of coastal wetlands enable coexistence of many species. Fig. 9–4a © Brooks/Cole Publishing Company / ITP Resource Partitioning Five species of insect–eating warblers are able to coexist in spruce forest of Maine. • Each species minimizes competition with others for food by spending majority of feeding time in a distinct portion of spruce trees (shaded areas) • Each also consumes somewhat different insect species. Fig. 9–5 © Brooks/Cole Publishing Company / ITP Resource Partitioning Fig. 9–5 (continued) © Brooks/Cole Publishing Company / ITP Character Displacement Over many years coexisting species tend to evolve physical and behavioral adaptations to minimize competition. Example: Darwin's finches on the same island have evolved different bill sizes and eat different size prey. Fig. 9–6. © Brooks/Cole Publishing Company / ITP Principle of Competitive Exclusion G.P. Gausse, in a classical experiment (1934), showed that two species with identical niches can not coexist indefinitely- principle of competitive exclusion. Fig. 9–3 © Brooks/Cole Publishing Company / ITP Types of Species Interactions – Predation- members of one species (predator) feed on another species (prey) Example: lion feeding on zebra At the population level, predation plays a role in evolution by natural selection Predators often kill the sick, weak, least fit members of a population Helps successful genetic traits to become more dominant in the prey population Predation •Predators tend to evolve characteristics for efficient capture of prey (keen eyesight, speed, etc.). •Prey tend to evolve characteristics to avoid being eaten (camouflage, chemical defenses, behaviors that startle predators, keen sense of smell, etc.). © Brooks/Cole Publishing Company / ITP Types of Species Interactions Major types of biotic interactions (cont’d): • Symbiosis- a long–lasting relationship in which species live together in intimate association: - Parasitism- one organism (parasite) lives on part of another organism (host) - Mutualism- two species interacting in a way that benefits both - Commensalism- one organism benefits from another, but neither helps nor harms the other organism © Brooks/Cole Publishing Company / ITP 4. Symbiotic Species Interactions Parasitism can be viewed as a special type of predation wherein the parasite: 1) is usually smaller than the prey 2) remains closely associated with the prey over time, and 3) rarely kills its host. • Endoparasites- live inside their host, e.g., tapeworm living in the gut; Plasmodium living inside a vertebrate and causing malaria. • Ectoparasites- live outside their host, e.g., mosquito feeding on the blood of mammal; lamprey attaching to outside of a host fish © Brooks/Cole Publishing Company / ITP Mutualism Mutualism is a relationship in which both species benefit. • Obligatory mutualism- results when two organisms can not live without each other; Example: in lichens an algae provides photosynthesis and a fungi provides a home for the algae Example: Rhizobium bacteria, in legume plant root nodules, fix nitrogen and legume provides carbohydrates and home Example: termites have gut organism that can digest cellulose • In other mutualisms the organisms can live apart, but there is strong mutual benefit in the relationship Example: flowering plants and their pollinators, plant gets pollinated, pollinator gets nectar or pollen to eat © Brooks/Cole Publishing Company / ITP Mutualism There are many more classic examples of mutualism. • Oxpecker bird feeds on the parasitic ticks of various large mammals in Africa, such as the black rhinoceros • Mycorrhizal fungi live in the roots of various plants; the fungus gets carbohydrates and the plant gets better absorption of nutrients by the fungal mat that extends beyond the roots • Clownfish in the coral reefs of Australia; clownfish gains protection from stinging tentacles and food when the anemone feeds; the anemone gains protection from various fish that feed on sea anemones © Brooks/Cole Publishing Company / ITP Commensalism Commensalism is a relationship in which one species benefits while another is neither helped not harmed to a significant degree. • Redwood sorrel, a small herbaceous plant, benefits from growing in the shade of tall redwoods, but the redwoods are not affected; • Epiphytes (orchids and bromeliads) grow in trees in the tropical rain forest gain a favorable place to live; whereas the tree is not affected **If epiphytes become abundant to block light, the tree can be negatively affected, and this becomes an example of competition. © Brooks/Cole Publishing Company / ITP 5. Succession Succession- gradual and fairly predictable change in species composition with time. • Some species colonize and become more abundant; • Other species decline or even disappear. Two kinds of succession: • Primary succession- gradual establishment of biotic communities in an area where no life existed beforeNO SOIL! • Secondary succession- gradual reestablishment of biotic communities in an area where a biotic community was previously presentSOIL ALREADY ESTABLISHED © Brooks/Cole Publishing Company / ITP Primary Succession Primary succession occurs with time in lifeless areas. • Newly formed islands and succession after the retreat of a glacier •Early successional speciestypically lichens and mosses first colonize bare rock--the first species to colonize are termed pioneer species •Mid: later small herbs and shrubs colonize •Late: finally tree species colonize • Takes lots of time 1 inch of soil can take 200-1000 yrs. to form. © Brooks/Cole Publishing Company / ITP Primary Succession Primary succession over several hundred years on bare rock exposed by a retreating glacier on Isle Royal in northern Lake Superior. Fig. 9–19 © Brooks/Cole Publishing Company / ITP Primary Succession Greatly simplified view of primary succession in a newly created pond in a temperate area. Nutrient rich bottom sediment is shown in dark brown. Fig. 9–20a © Brooks/Cole Publishing Company / ITP Secondary Succession Secondary succession occurs where the natural community of organisms has been disturbed, removed, or destroyed. • Agricultural fields go through succession. • Succession proceeds until an area is occupied by a climax community, however recent views recognize that a single climax is not predictable. • Not as lengthy process as primary due to existence of soil. © Brooks/Cole Publishing Company / ITP Secondary Succession Secondary succession over 150–200 years in an abandoned farm field in North Carolina. Fig. 9–21 © Brooks/Cole Publishing Company / ITP Secondary Succession Successional changes in the animal community accompany successional changes in the plant community. Fig. 9–22 © Brooks/Cole Publishing Company / ITP Table 8-1 Ecosystem Characteristics at Immature and Mature Stages of Ecological Succession Characteristic Ecosystem Structure Plant size Species diversity Trophic structure Ecological niches Community organization (number of interconnecting links) Table 8-1 Page 158 Immature Ecosystem (Early Successional Stage) Mature Ecosystem (Late Successional Stage) Small Large Low High Mostly producers, few decomposers Mixture of producers, consumers, and decomposers Few, mostly generalized Many, mostly specialized Low High Ecosystem Function Biomass Net primary productivity Food chains and webs Low High High Low Simple, mostly plant with few decomposers herbivore Complex, dominated by decomposers Efficiency of nutrient recycling Low High Efficiency of energy use High Low Disturbance What is the role of disturbance in succession? • Disturbance- a discrete event that disrupts an ecosystem or community •Fires, hurricanes, tornadoes, droughts and floods •Human–caused disturbance: deforestation, overgrazing, plowing •Initiates secondary succession by eliminating part or all of the existing community, and by changing conditions and releasing resources. © Brooks/Cole Publishing Company / ITP Mechanisms of Succession Both primary and secondary succession are driven by three mechanisms: • Facilitation- a process by which an earlier successional species makes the environment suitable for later successional species; e.g., legumes fixing nitrogen can enable later successional species. • Inhibition- a process whereby one species hinders the establishment and growth of other species; e.g., shade of late successional trees inhibits the growth of early successional trees; • Tolerance- a process whereby later successional species are unaffected by earlier successional species. © Brooks/Cole Publishing Company / ITP Changes During Succession During succession species diversity and stratification tend to increase, while growth rates and primary productivity tend to decrease. **See Table 8-1 Fig. 9–23 © Brooks/Cole Publishing Company / ITP 6. Island Biogeography In the species equilibrium model of island biogeography (developed by Robert MacArthur and Edward O. Wilson) the number of species on an island is determined by the balance between immigration and extinction. Fig. 9–24 © Brooks/Cole Publishing Company / ITP Island Biogeography Small islands are expected to have lower immigration rates and higher extinction rates, and hence fewer species than large islands. Fig. 9–24 © Brooks/Cole Publishing Company / ITP Island Biogeography Far islands are expected to have lower immigration rates, and hence fewer species than near islands. Fig. 9–24 © Brooks/Cole Publishing Company / ITP Case Study: Hawaii Pre-human Hawaii had great native biodiversity before Polynesian seafarers arrived around A.D. 400. Today it is “synthetic.” Island biogeography dictates that these islands far from the mainland would have very little possibility of species naturally immigrating. Humans did. WE were an invasive, nonnative species here 1500 years ago. Case Study: Hawaii Islands have been further overrun by nonnative species we carried, introduced accidentally or intentionally. It was a popular stopover in Pacific travels. – Of the original 145 endemic birds only 35 remain, 24 of which are endangered – Of the 1900 flowering plant species today, over 900 are alien and are dominating over the rest – Of the 8800 insect and arthropod species, over 3000 are of alien origin – Ants, the leading predators of insects, never used to inhabit Hawaii, but are now wreaking havoc on their insect populations – Feral pigs, not on the island until they were brought by humans, are also causing huge problems with destroying vegetation. Island Biogeography The model of island biogeography has been widely applied in conservation biology by viewing the landscape as composed of habitat islands separated by an ocean of degraded or unsuitable habitat modified by human activity. • Large habitat patches tend to have more species • Habitat patches that are near larger intact habitat areas tend to have more species • These principles can be applied to land preservation and management efforts. © Brooks/Cole Publishing Company / ITP 7. Stability and Sustainability Stability has three aspects: • Inertia (or persistence)- the ability of a system to resist being disturbed or altered • Constancy- the ability of a living system to maintain a certain size or state • Resilience- the ability of a living system to recover after a disturbance © Brooks/Cole Publishing Company / ITP Stability and Sustainability Signs of poor health or stressed ecosystems: – Decrease in primary productivity – Increased nutrient losses – Decline or extinction of indicator species – Increased populations of pests or disease organisms; – Decline in species diversity – Presence of contaminants. Through an understanding of ecology we can grapple with what it means to have sustainable ecosystems.