Interactions in ecosystems

habitat Combined biotic and abiotic factors found in the area where an organism lives

Ecological niche All of the physical, chemical, and biological factors that a species needs to survive, stay healthy, and reproduce in an ecosystem Food Abiotic factors Behavior The physical characteristics of the area where the species lives Size Location Temperature pH The function of the species in the biological community

Fundamental Niche The largest ecological niche where an organism or species can live without competition

Realized Niche As a result of competition in the species’ fundamental niche, a realized niche is the: Range of resources that a species uses Conditions that the species can tolerate Functional roles that the species plays

Competitive exclusion Theory that states that no two species can occupy the same niche at the same time Niche partitioning: two species naturally divide different resources based on competitive advantages Evolutionary response: two species may have experienced divergent evolution

Competitive Exclusion The exclusion of one species by another due to competition When can competitors coexist? If they use a realized niche as opposed to a fundamental niche

Realized Niche/Fundamental Niche 2 species of barnacles that grow on the same rocks on the coast of Scotland Chthamalus stellatus lives in shallow water, exposed to receding tides Semibalanus balanoides lives lower down on the rocks, rarely exposed to the atmosphere When Semibalanus is removed from the deeper zone, Chthamalus occupies the vacant surfaces Chthamalus’ fundamental niche includes the deeper zone When Semibalanus was reintroduced, it out-competed Chthamalus for the deeper zone Semibalanus, in contrast, could not survive in the shallow-water habitats when Chthamalus was removed Competition can limit how a species uses its resources

Realized Niche/Fundamental Niche

Ecological equivalents Organisms that share a similar niche but live in different geographical regions

Competition & predation are two important ways in which organisms interact

Competition The relationship between species that attempt to use the same limited resource Resources often competed over: Food Nesting sites Living space Light Mineral nutrients Water

predation Process by which one organism hunts and kills another organism for food

Symbiosis Ecological relationship between members of at least two different species that live in direct contact with one another

Symbiosis: Mutualism A relationship between two species in which both species benefit Example: ants and aphids Aphids give ants food Ants give aphids protection from predators

Symbiosis: Commensalism A relationship between two organisms in which one organism benefits and the other is neither harmed nor helped Example: tropical fishes and sea anemones Fish are protected Anemone is neither harmed nor helped

Symbiosis: Parasitism One organism feeds on and usually lives on or in another, typically larger organism Do not usually kill their prey (“host”) Depend on the host for food and a place to live Host often serves to transmit the parasite’s offspring to new hosts

Symbiotic relationships

Population Density The number of individuals of the same species that live in a given unit of area If the individuals of a population are few and are spaced widely apart, they may seldom encounter one another, making reproduction rare

Geographic dispersion of a population shows how individuals in a population are spaced

Survivorship curves help to describe the reproductive strategy of a species Type I Common in large mammals Low infant mortality Many survive to old age Parental care Type II Reptiles (including birds), small mammals At all times species have equal chance for living and dying Type III Invertebrates, fishes, amphibians, plants High infant mortality Few survive to adulthood

r-strategists A species that is adapted for living in an environment where changes are rapid and unpredictable; characterized by: Rapid growth High fertility Short life span Small body size Exponential population growth Example: insects

k-strategists A species characterized by: Slow maturation Few young Slow population growth Reproduction late in life Population density near the carrying capacity of the environment Examples: bears, elephants, humans

Population growth patterns

Changes in a population’s size are determined by… Immigration Births Emigration Deaths

Population growth is based on available resources

Population Model Hypothetical model of the population Attempts to exhibit the key characteristics of a real population By making a change in the model and observing the outcome, demographers can predict what might occur in a real population

Growth Rate In a given period of time a population… Grows when more individuals are born than die (Born > Die) Reduces in size when more individuals die than are born (Born < Die) Stays the same size when the number of individuals that are born equal the number that die (Born = Die)

Population Growth A population model describes the rate of population growth The difference between the birthrate and the death rate Birthrate – Death rate

Population Growth Models Simple Model (Part I): Calculating the population growth rate r(rate of growth) = birthrate – death rate Simple Model (Part II): Exponential growth curve ∆ N (change in population) = rN More realistic model: Logistic model ∆ N = rN (K-N)/K

Exponential Growth Curve Dramatic increase in population over a short period of time A single bacteria cell that divides every 30 minutes will produce more than 1 million bacteria after only 10 hours

Exponential Growth Curve The number of individuals that will be added to the population as it grows Multiply the size of the current population (N) by the rate of growth (r)

Logistic growth Population growth that is characterized by a period of slow growth, followed by a period of exponential growth, followed by a period of almost no growth

Logistic Model A model of population growth that assumes: Finite resource levels limit population growth Birthrates and death rates vary with population size When a population is below carrying capacity, the growth rate is rapid

Logistic Model As the population approaches carrying capacity, death rates begin to rise and birthrates begin to decline…the rate of growth slows The population eventually stops growing when the birthrate equals the death rate In real situations, the population may, for a short time, exceed the carrying capacity

Logistic Model If this happens, deaths will increase and outnumber births until the population falls down to the carrying capacity Many scientists are concerned that Earth’s human population may have exceeded its carrying capacity (reached 6 billion in 1999)

Carrying Capacity (K) The largest population that an environment can support at any given time Populations do not usually grow unchecked

Carrying Capacity (K) Growth is limited by: Predators Disease Availability of resources

Population crash Dramatic decline in the size of a population over a short period of time

Ecological factors limit population growth Limiting factor: environmental factor that limits the growth and size of a population

Density-dependent limiting factors Environmental resistance that affects a population that has become overly crowded Competition Predation Parasitism and disease Resources in short supply eventually become depleted as a population grows Examples: food and water

Density-independent limiting factors Environmental resistance that affects a population regardless of population density Unusual weather Natural disasters Human activities Mosquito populations increase in the summer while the weather is warm, but decrease in the winter

Succession occurs following a disturbance in an ecosystem Sequence of biological changes that regenerate a damaged community or start a community in a previously uninhabited area

Succession The replacement of one type of community by another at a single location over a period of time Species replacement

Pioneer Species A species that colonizes an uninhabited area and starts an ecological cycle in which many other species become established Occurs when a volcano forms a new island, a glacier recedes and exposes bare rock, or a fire burns all of the vegetation in an area… Pioneer species tend to be small, fast-growing plants They make the ground more hospitable for other species

Primary Succession Succession that begins in an area the previously did not support life

Secondary Succession The process by which one community replaces another community that has been partially or totally destroyed