Interactions in Populations Chapter 14

Habitat and Niche Habitat Niche All the biotic and abiotic factors in an area where an organism lives Niche All the physical, chemical, and biological factors needed to survive Habitat is where an organism lives Niche is how an organism survives A niche includes food, abiotic conditions, and behavior (reproduction activities)

Habitat and Niche Competitive Exclusion Principle Two species competing for the same resources One will be better suited than the other One species will be pushed into another niche The reason you have this is because of the fact eventually there will be a winner and a loser One species will somehow have an ever so slight advantage over the other species and will either go extinct or evolve. This is also known as Gause’s law.

Habitat and Niche Secondary Outcomes of Competitive Exclusion Niche Partitioning Dividing the niche so two species can share Evolutionary Response Divergent evolution could take place to allow two species to survive

Habitat and Niche Ecological Equivalants Similar species with similar niches in different geographical regions Sign of convergent evolution Emerald Tree Boa – South America Convergent evolution – similar species must adapt to environments in different areas – kit fox and red fox Green Tree Python - Australia

Community Interactions Competition – when organisms try to use the same ecological resources Resources – any necessity of life Interspecific Competition Intraspecific Competition Direct competition will often result in a winner and a loser – eventually Resources – water, nutrients, light, food, space Interspecific – two different species compete for a resource - space Intraspcific – members of the same species compete for a resource – water, birds with mates

Community Interactions Predation – one organism captures and feeds on another Predator Prey

Community Interactions Symbiosis – any relationship where two species live closely together There are different types of symbiosis mutualism commensualism parasitism Symbiotic relationships are essential to any ecosystem

Community Interactions Mutualism – both species benefit Flowers and bees Clownfish and anemones Tangs and cleaner shrimp

Community Interactions Commensalism – one species benefits the other is unharmed Sharks and ramoras Barnacles and whales

Community Interactions Parasitism – one species benefits and the other is harmed One organism lives in or on another organism harming it along the way Tapeworms, fleas, ticks, lice

Population Density and Distribution Characteristics of Populations Geographic distribution – the area inhabited by a population Population density – the number of individuals per unit area Population – a group of individuals of the same species living in the same area Four main characteristics of a Population – geographic distribution, population density, growth rate, and a population’s age. Geographic distribution can range from a few centimeters to millions of square kilometers.

Population Density and Distribution Population Dispersion The amount populations are spread out in relation to one another Clumped Uniform Random Clumped – live close together in groups-facilitates mating, gains protection, access to food resources Uniform – territoriality and intraspecies competition leads to this; specific distances from one another Random – Random distribution around an area

Population Density and Distribution Survivorship Curves Number of individuals surviving over time Type I Type II Type III

Population Density and Distribution Type I Common among large mammals Low infant mortality Generally long life

Population Density and Distribution Type II Birds, small mammals, some reptiles Constant threat of death

Population Density and Distribution Type III Invertebrates, fish, amphibians, plants High infant mortality rate

Population Growth Patterns Population Growth – birth rate, death rate, or migration Immigration – the movement into an area Emigration - the movement out of a area Populations may stay at or near the same amount for some time or they may fluctuate greatly over many years. There are three factors that can affect the population size: 1. Births 2. Deaths 3. Movement into or out of the population. Basically, a population varies based upon the number of individuals added or removed from the population.

Population Growth Patterns Exponential Growth – individuals reproduce at a constant rate Under ideal conditions, a population will grow exponentially. Suppose a bacteria has a doubling time of 20 minutes – 1 will be come 2 in 20 min. etc. In one hour there will be 64 bacteria, in one day there will be 4.7 x 1021 bacteria present This is how you get infections that can be extremely serious. If this were graphed out (number vs. time), the graph would look like a J Due to the constant reproduction of individuals, the growth initially is very slow but eventually it will grow infinitely.

Population Growth Patterns Logistic Growth – populations growth slows or stops following a period of exponential growth Carrying capacity – the largest number of individuals that the environment can support Population Crash Exponential growth would result in the bacteria discussed covering the earth – obviously this hasn’t happened. After a period of exponential growth, the population growth will start to slow due to resources not being as abundant. This leads to an S-shaped curve which signifies logistic growth – exponential growth followed by logistic growth. This is not to say there are not fluctuations in the population – the losses and additions just tend to average out. There will be a point at which the number of individuals within an ecosystem is at a max – carrying capacity. Population crash – a dramatic decline in the population due to a sudden drop in carrying capacity – could be due to a sudden drop in food amounts

Population Growth Patterns Limiting Factors – something that causes population growth to decrease Limiting factors can be food, pressure from predators, availability of shelters. These particular factors can affect the long term survival of a species.

Population Growth Patterns Patterns of Population Growth Demography – the scientific study of human populations Scientists have figured out that the population will not grow forever, but what will limit the growth or keep it in check? There are certain criteria that that scientists look at to determine the growth – birth rates, death rates, age of the population

Population Growth Patterns Demographic Transition – a dramatic change in the birth and death rates U.S., Europe, and Japan China and India Because of advances in medicine and health, birth rates are starting to far outweigh the death rates – this leads to rapid increases in populations. Eventually, as societies modernize, increase their education levels, and raise the standard of living then they have less children – this causes the birth rate to fall until it meets the death rate – this is when the demographic transition is complete.

Population Growth Patterns Age Structure What does it mean if there are lots of older people? What does it mean if there are lots of younger people? Age structure diagram The graph in the middle suggests that a slow steady growth will occur The graph on the left suggests that the population may double in the futures

Population Growth Patterns Future Population Growth Is the human population increasing? Will the human population continue to increase forever? What factors will cause the human population to slow? The population is currently growing and may be over 9 billion by 2050

Population Growth Patterns Density-dependent factors – limiting factor that depends on population size This may include competition, predation, parasitism, and disease These factors only come into play when the population reaches a certain size.

Population Growth Patterns Density-independent factors – factors that affect all populations regardless of size Weather Natural disaster Seasons Human activities Human interactions such as hunting, damming rivers and streams, or cutting down forests.

Ecological Succession Often times when we view an ecosystem we look at it has always been the way it appears However, every ecosystem is always changing – in response to human intervention, and natural occurences. Not every thing dies at the same time or at the same rate. This is what we call ecological succession - a series of predictable changes in the physical environment

Ecological Succession Primary Succession – new species grow where no soil exists This is the type of succession that occurred after Mt. St. Helens – the land was covered with volcanic ash and lava, there was no dirt. The first species to populate an area under primary succession is called the pioneer species. Often these are lichens – organisms made from fungus and algae that are closely related to bacteria and can perform photosynthesis. As these grow they will break up rock and create soil.

Ecological Succession Secondary Succession – a disturbance changes the existing community without removing the soil Land cleared by plowing for farming and then left abandoned Also occurs when wildfires burn down forrests Some seeds have even evolved to the point that they will not sprout unless exposed to fire