Chap 54

• Ecology is the study of how organisms relate to one another and to their environments.
• The key elements of the environment are temperature, water, sunlight and soil.
• Homeostasis is when Individual must maintain a steady state internal environment regardless of external environment. Their insides stats alway have to stay the same.
• Conformers is any organism whose internal environment is highly influenced by external factors (adopt temperature, salinity of their surroundings).
• Responses to environmental variation can be short or long term.

  Short term - From a few minutes, to an individual’s lifetime, variety of ways to cope.

  Long term - Natural selection can operate to make a population better adapted to the environment.
• Coping Mechanisms for organisms in environmental change (short term)

  1. Physiological responses - Sweating, increased erythrocyte production, making “antifreeze”.

  2. Morphological capabilities - Endotherms (animals that maintain constant internal pressure) have adaptations that minimize energy expenditure like Thick fur coats during the winter.

  3. Behavioral responses - Moving from one habitat to another.
• Natural selection leads to evolutionary adaptation to environmental conditions.

  • We can see this in closely related species that live in different environments.
  • Allen’s rule of reduced surface area: Mammals from colder climates have shorter ears and limbs.
  • Desert frogs: evolved a greatly reduced rate of water loss through skin. (cause they live in the desert)
• Populations - groups of individuals in one place and time. (same species)
• 3 characteristics of population ecology

  1. Population range - area throughout which a population occurs.
  2. Pattern of spacing of individuals.
  3. How population changes in size through time.
• Range (Characteristics of Population Ecology)

  • Most species have limited geographic range.
  • Ranges change through time because of environment changes, humans activity, and when animals overtake/colonize previously inhospitable habitats.
• Range (Characteristics of Population Ecology)

  • Northward Expansion of Trees - The environment changed after the glaciers retreated and plant/animal population expanded northward.
  • The cattle egret expanded its range across an ocean, from Africa to South America, and continues to expand its range northward.
• Range (Characteristics of Population Ecology)

  Dispersal Methods

  1. Lizards colonized distant islands due to individuals or eggs floating or drifting on vegetation
  2. Seeds of plants disperse in many ways (Windblown, Adherent, Fleshy)
• Pattern Spacing (Characteristics of Population Ecology)

  Individuals in populations exhibit different spacing patterns

  • Random spacing - individuals do not interact strongly with one

  another; not common in nature.

  • Uniform spacing - behavioral interactions, resource competition.

  • Clumped spacing - uneven distribution of resources; common in nature
• Pattern Spacing (Characteristics of Population Ecology)

  • Metapopulations - Occur in areas in which suitable habitat is patchily distributed and is separated by intervening stretches of unsuitable habitat (butterflies moving)
  • Dispersal of Organisms-
  • Interaction may not be symmetrical.
  • Populations increase and send out many dispersers.
  • Individual populations may become extinct.
  • Population bottlenecks may occur
  • Small populations have few dispersers.
• Pattern Spacing (Characteristics of Population Ecology)

  Metapopulations can have two implications for the range of a species

  • Continuous colonization of empty patches prevents long-term extinction.

  • In source–sink metapopulations, the species occupies a larger area than it otherwise might

  Source–sink metapopulations

  • Some areas are suitable for long-term habitat, others are not.

  • Populations in better areas (source) bolster the population in poorer areas (sink) by dispersing healthy organisms.
• Population Demography/Size (Characteristics of Population Ecology)

  Demography - Quantitative study of populations.

  (How size changes through time)

  Whole population: increasing, decreasing, remaining constant. (Population broken down into parts)
• Population Demography/Size (Characteristics of Population Ecology)

  • Population growth can be influenced by the population’s sex ratio • Number of births directly related to number of females.
  • Generation times: average interval between birth of an individual and birth of its offspring
  • Populations with short generations can increase in size more quickly than populations with long generations.
• Age Structure Determined by the numbers of individuals in a different age group

  • Cohort: group of individuals of the same age
  • Fecundity: number of offspring produced in a standard time
  • Mortality: death rate in a standard time
• Population Demography/Size (Characteristics of Population Ecology)

  • Survivorship - percent of an original population that survives to a given age.
  • Survivorship curve - Express some aspects of age distribution.
• Survivorship Curves

  Survivorship curves can be classified into three general types

  Type 1: low death rates during early and middle life and an increase in death rates among older age groups (Humans)

  Type 2: a constant death rate over the organism’s life span (Rodents)

  Type 3: high death rates for the young and a lower death rate for survivors (Oysters)

  Many species are intermediate to these curves
• Life History

  Natural selection favors traits that maximize the number of surviving offspring left in the next generation by an individual organism

  Two factors affect this quantity.

  1. How long an individual lives.

  2. How many young it produces each year.
• Life history - Complete life cycle of an organism.

  Trade-off: limited resources vs increased reproduction

  Would you rather have more resources for you or more babies?
• Survival of Offspring

  • In terms of natural selection, how many offspring themselves survive to reproduce is more important than the number of offspring produced.
  • Balance between number of offspring and size of offspring
  • Larger offspring have a greater chance of survival because producing many small offspring may result in very low survival rates.
• Age at First Reproduction

  Age at first reproduction correlates with life span

  • Long-lived species delay reproduction
  • Advantage: juveniles gain experience before high cost of reproduction.
  • • Short-lived species reproduce early
  • • Time is important; delay may mean no offspring.
• Environmental Limits to Population Growth

  • Populations often remain the same size regardless of the number of offspring born
  • Exponential growth model applies to populations with no growth limits:
  • r = (b − d) + ( i − e)
  • r = rate of population increase
  • b = birth rate
  • d = death rate
  • i = immigration
  • e = emigration
• Biotic Potential (the unrestricted growth of populations resulting in the maximum growth of that populatio)

  • Biotic potential: e = i
• Biotic Potential (the unrestricted growth of populations resulting in the maximum growth of that population)

  • Biotic potential: e = i
  • dN/dt = riN
  • N - number of individuals in the population
  • dN/dt the rate of change over time
  • ri is the intrinsic rate of natural increase for the population
• Carrying Capacity

  • The biotic potential of any population is exponential, even when the rate of increase remains constant
  • Result of unchecked exponential growth is a population explosion.
  • • Carrying capacity: symbolized by K, is the maximum number of individuals that the environment can support
• Logistic Growth Model

  • Logistic growth model: applies to populations as they reach K (carrying capacity)
  • dN/dt = rN (K - N)/K
  • dn/dt is equal to intrinsic rate of natural 𝑑𝑡 increase, adjusted for the amount of available resources
  • r = rate of population increase
  • N = the number of individuals in the population
  • K = Carry Capacity
• Logistic Growth Model

  • As N approaches K, the rate of population growth begins to slow If N = K the population growth rate is zero
  • If the population size exceeds K, the population size will decline until it reaches K.
• Density

  • Density-dependent (K-selection) • Factors that affect the population and depend on population size.
  • Density-independent (r-selection) • Other factors, such as natural disasters, affect populations regardless of size.
• Density-Independent Effects (r - selected)

  • Rate of growth of a population at any instant is limited by something unrelated to the size of the population
  • External environment aspects: cold winters, droughts, storms, volcanic eruptions
  • Populations display erratic growth patterns because of these events
• Resource Availability

  Resource availability affects life history adaptations

  • When resources are limited, the cost of reproduction is high
  • Selection will favor individuals that can compete and utilize resources efficiently.
  • • K-selected populations: adapted to thrive when population is near its carrying capacity
• r-Selected Populations

  • Populations far below carrying capacity, resources abundant
  • Costs of reproduction are low
  • r-selected populations: selection favors individuals with the highest reproductive rates.
  • Most natural populations show life history adaptations that exist along a continuum of rand K-selected traits.
• Human Population

  • Growth K-selected life history traits
  • Small brood size.
  • • Late reproduction.
  • • High degree of parental care.
  • Changes since the 1700s allowed humans to escape logistic growth
  • Human populations have grown exponentially
  • • Birth rate has remained unchanged
  • • Death rate has fallen dramatically
• World Population Growth Rate

  World population growth rate is declining

  • High of 2.0% in 1965–1970.

  • 1.1% in 2015.

  • Still an increase of 75 million people per year.
• Consumption

  Consumption in the developed world further depletes resources

  • Wealthiest 20% of the world’s population accounts for 86% consumption of resources and produces 53% of CO2 emissions. •
  • Poorest countries: 20% is responsible for 1.3% consumption and 3% CO2 emissions.
• Which of the following explains why you might expect the number of individuals in a population to increase exponentially but you should expect the number of tables that a carpenter produces to increase linearly?

  Organisms can make more organisms, but tables cannot make more tables.
• Which environment would most likely support a metapopulation?

  A series of nearby caves
• Human population growth was slow and gradual before the 1800s, but since then has been exponentially increasing.