What Shapes an Ecosystem?

Review of Biotic and Abiotic Factors Ecosystems are influenced by a combination of biological and physical factors. Biotic factors –include all the living things with which an organism might interact. Abiotic Factors –Physical, or nonliving, factors that shape ecosystems.

Habitat and Niche Habitat –all aspects of the area in which an organism lives (includes both biotic and abiotic). –Habitats may change or disappear due to natural causes or interference by man.

Habitat and Niche Niche –the role or place and position a species has in its environment. An ecological niche includes all of the factors that a species needs to survive, stay healthy, and reproduce. –food –abiotic conditions –behavior

Habitat and Niche Why do you think no two species can share the same niche. One species is better suited to the niche and the other will either be pushed out or become extinct.

Community Interactions When organisms live together in ecological communities, they interact constantly. Community interactions include: –Competition –Predation –Symbiosis

Community Interactions Competition: –occurs when two organisms fight for the same limited resource. –Direct competition in nature often results in a winner and a loser—with the losing organism failing to survive.

How species avoid Competition The distribution of these warblers avoids direct competition, because each species feeds in a different part of the tree.

Community Interactions Predation: –occurs when one organism captures and eats another. Predator Prey

Community Interactions Symbiosis: –Any relationship in which two species live closely together –Includes: –mutualism –commensalism –parasitism

Community Interactions Mutualism: –both species benefit from the relationship.

Community Interactions Commensalism –one member of the association benefits and the other is neither helped nor harmed. Human Our eyelashes are home to tiny mites that feast on oil secretions and dead skin. Without harming us, up to 20 mites may be living in one eyelash follicle. Demodicids Eyelash mites find all they need to survive in the tiny follicles of eyelashes. Magnified here 225 times, these creatures measure 0.4 mm in length and can be seen only with a microscope. + Organism benefits + Ø Ø Organism is not affected Commensalism

Community Interactions Parasitism –one organism lives on or inside another organism and harms it. Organism benefits 0 _ Organism is not affected Hornworm caterpillar The host hornworm will eventually die as its organs are consumed by wasp larvae. Braconid wasp Braconid larvae feed on their host and release themselves shortly before reaching the pupae stage of development. _ Parasitism + 0

Ecological Succession Succession occurs following a disturbance in an ecosystem and regenerates or creates a community after a disturbance. –a sequence of biotic changes –damaged communities are regenerated –new communities arise in previously uninhabited areas

Ecological Succession There are two types of succession. primary succession — started by pioneer species

Ecological Succession There are two types of succession. –secondary succession — started by remaining species

Population Ecology

Population Dynamics Population: –All the individuals of a species that live together in an area Demography: –The statistical study of populations, allows predictions to be made about how a population will change

Population Dynamics Three Key Features of Populations –Size –Density –Dispersion

Three Key Features of Populations Size: number of individuals in an area

Three Key Features of Populations Growth Rate: –Birth Rate (natality) - Death Rate (mortality) –How many individuals are born vs. how many die –Birth rate (b) − death rate (d) = rate of natural increase (r)

Density: measurement of population per unit area or unit volume Pop. Density = # of individuals ÷ unit of space Three Key Features of Populations

1.Immigration: movement of individuals into a population 2.Emigration: movement of individuals out of a population 3.Density-dependent factors: Biotic factors in the environment that have an increasing effect as population size increases (disease, competition, parasites) 4.Density-independent factors: Abiotic factors in the environment that affect populations regardless of their density (temperature, weather) How Do You Affect Density?

Immigration Emigration Natality Mortality Population Factors That Affect Future Population Growth

Population Dispersion

Dispersion: describes the spacing of organisms relative to each other –Clumped –Uniform –Random Three Key Features of Populations

Population density = number of individuals in a given area or volume Count all the individuals in a population Estimate by sampling Mark-Recapture Method How Are Populations Measured?

Idealized models describe two kinds of population growth: 1.Exponential Growth 2. Logistic Growth How Do Populations Grow?

Carrying Capacity Carrying Capacity (k): –The maximum population size that can be supported by the available resources –There can only be as many organisms as the environmental resources can support

Figure 35.3A Exponential Growth Curve - J curve

Logistic Growth Curve – S curve

Declining birth rate or increasing death rate are caused by several factors including: –Limited food supply –The buildup of toxic wastes –Increased disease –Predation Factors Limiting Growth Rate

“Booms” and “Busts”

R Strategists  Short life span  Small body size  Reproduce quickly  Have many young  Little parental care  Ex: cockroaches, weeds, bacteria Reproductive Strategies

K Strategists  Long life span  Large body size  Reproduce slowly  Have few young  Provides parental care  Ex: humans, elephants

Age Distribution Distribution of males and females in each age group of a population Used to predict future population growth

Human Population Growth J curve growth (exponential growth curve) Grows at a rate of about 80 million yearly –r =1.3% Why doesn’t environmental resistance take effect? –Altering their environment –Technological advances The cultural revolution The agricultural revolution The industrial-medical revolution

Doubled three times in the last three centuries About 6.1 billion and may reach 9.3 billion by the year 2050 Improved health and technology have lowered death rates The Human Population

History of the Human Population