Human Ecology I Flashcards
Human Ecology 1: Roadmap
What is human ecology?
Relationship of ecology to evolution?
Macro human changes in relationship with environment
(hominin evolution/speciation)
Responses to environments: levels & variation (adaptation, acclimation & acclimatization)
Following lectures will explore principles & examples of ecology / evolution interface
Today: relationship of ecological processes to early human
evolution
What is ecology?
What is ecology?
Relationship of organism to its environment
physical biological
social environment
“Study of factors determining the numbers and distribution
of organism or organisms”
Why is ecology important?
The day-to-day workings of natural
selection
Review: Natural selection (= individual selection)
“THE CHANGE IN FREQUENCY (therefore RELATIVE) OF GENOTYPES WITHIN A POPULATION FROM ONE GENERATION TO THE NEXT, RESULTING FROM DIFFERENCES IN THE ABILITY OF THEIR PHENOTYPES TO PRODUCE SURVIVING OFFSPRING” NOT THE SPECIES *
How did individuals with that behaviour survive and reproduce better than other individuals in same population (same time in the same environment) without that behaviour?
What is human ecology?
Inter-relationships between humans and their environment
In an evolutionary context (aspects of the environment as selective pressures)
Biological ecology - how the environment has shaped/shapes
our biology
Evolutionary ecology : evolution of behaviour and morphology relative to environmental change & variation (biological ecology over evolutionary time scale)
Cultural ecology: environmental shaping of socially transmitted information (e.g. social structure, political structures, economy, etc) an extension relevant to organisms with social learning.
Adaptation (across generations)
Adaptation as a Process (verb):
“The process of successful interaction between an environment and a population”
Result of the process (noun):
“Cultural or biological traits that offer an advantage in a given environment”
Average fitness over generations in a stable environment
Via Natural selection from 1 generation to the next.
Acclimation
Very short term response (minutes to hours) to environmental stressor
adrenalin response to threat male testosterone surge in response to physical confrontation sweating to increase evaporative cooling
Usually physiology is species-wide but can also vary quantitatively by
population or developmental stage
These are genetic adaptations that allow phenotypic change in individuals in response to environment and reversal of that change.
Ecological processes: interface of humans with environment
Natural selection is differential replication of genotypes by different phenotypes (i.e. individuals) in a particular environment
Result: populations change over time in response to ecology during each generation’s lifetime! particularly in changing environment (use of
resources), or changing levels of competition (ability to acquire resources)
Adaptation (genetic)
Competition: not all individuals are able to grow, survive and reproduce equally well
Some of these inequalities are due to their different abilities to convert resources into biomass and reproduction
When a particular resource is limiting; those better able to acquire/use it will survive, grow, repro more than those less able (natural selection)
Summary: Types and examples of genetic adaptation
Species - wide
very old = stereoscopic vision, opposable thumb, bipedality, voice, reduced body hair) variation but not geographically clustered clines
Population-specific more recent (since out of Africa dispersal)
since dispersion into various habitats genetic variation
(e.g. body shape, lactose tolerance; sickle cell; 02 saturation that Dr. Gaudieri told you about) more likely to be geographically clustered
Ecology & Adaptation
To persist over evolutionary time, an organism must:
Survive & Reproduce
Need: Food & water shelter
Mates
What makes that hard?
Environment
Hostile
Changing: adaptation to one condition may be negative when
condition changes
I
ncludes: Competitors
Most important competitors have same needs… i.e. conspecifics
Responses to the environment
Within an individual:
Acclimation = very short time scale within lifetime
Acclimatization = medium time scale within lifetime
Across generations:
Adaptation = intergenerational time scale
The ability to acclimate & acclimatize are adaptations.
The ability to respond to short term environmental stimuli evolved via selection when/where environments
are more variable on short time scales
Aclimatization
Slightly longer term (days to weeks) responses to short-term threats to homeostasis (= maintaining stability of physiological processes)
Phenotypic plasticity (change the phenotype)
Reversible physiological changes
e.g. skin tanning changes skin color and reduces damage from UV
Response doesn’t change genotype
Most are species-wide
Some are population-specific
Mechanisms are genetic adaptations that allow phenotypic change in individuals in response to environment cue
Population-specificPopulation-specific
Due to population-specific environments
More recent (within Homo sapiens)
Body shape (cold temperature)
Skin color variation (latitude, light, vitamins)
Post-weaning lactose tolerance (dairy husbandry)
Genetic variations associated
So, variations among populations are more recent than homogeneous traits of humans that vary from other species
(revise derived and ancestral traits)
There is much more variation within population than among populations!
More migration means less geographical differences
Humans over the planet are more are more genetically similar to each other than are populations of chimpanzees to each other within sub-Saharan 21
Africa.
A history of responses to environments
Largely, species wide adaptations to environment until 100-70 KYA
within Africa & response to climate changes.
Out of Africa: Some population wide & serial adaptations to differing environments (H. erectus
as well as e.g.
1) before humans arrive in western hemisphere, first experience environment of north Asia
2) moving north & south => seasonal environs
Also: Acclimatization and acclimation = plastic response to
varying environments (reversible physiological responses)
Recap
We have defined the concept of ecology.
We have linked the processes of ecology to evolution of populations through ecological effects on survival and reproduction.
We have reviewed the timing of human evolution to note that much of human evolution occurs during a geological period of much environmental variation over time & space.
We have reviewed our knowledge that populations evolve such that ancestral traits are the traits we all share due to common evolutionary history and derived traits within the species evolve as populations disperse and experience different conditions.
We established that humans respond to changes in their environments on varying timescales (within and across generations) via both genetic
change and plasticity
Adaptation is a genetic process that results in phenotypic traits that are better suited to an environment in accomplishing survival and reproduction.
A history of responses to environments
Largely, species wide adaptations to environment until 100-70 KYA
within Africa & response to climate changes.
Out of Africa: Some population wide & serial adaptations to differing environments (H. erectus as well as e.g.
1) before humans arrive in western hemisphere, first experience environment of north Asia
2) moving north & south => seasonal environs
Also: Acclimatization and aclimation = plastic response to
varying environments (reversible physiological responses)
Ecology 2: Roadmap
Humans are organisms who conform to laws of physics and the same basic requirements of most other living organisms
- particularly mammalian organisms with whom we share
millions of years of evolution.
Energy obtained from the sun via photosynthesizers (plants).
Laws of thermodynamics
Energy transformation
Entropy (organization requires energy)
Heat production through metabolism
Examples of adaptation to abiotic factors
Survival requires the transformation of energy and use of energy
Organisms transform energy into biomass (metabolism, biomass, offspring)
Transformation requires energy & specific resources that vary e.g.
plants require CO2, minerals, water and light to photosynthesize
animals require 02, water, minerals, carbon source (fixed energy), etc
Physics and Ecology
1st law of thermodynamics: conservation of energy in the conversion of energy from one form to another, energy is neither lost nor gained from a system
Think of biomass as standing stocks of energy
Can’t make new energy except through capture of solar energy.
Energy is fixed via photosynthesis by plants
2nd Law of Thermodynamics: energy conversions result in a loss of free energy in the system (increased entropy) or: it costs energy to maintain organization of systems because they naturally go toward a state of disorder….
Conversions of biomass cost energy: e.g. more energy arrives from sun than is converted by photosynthesis to plant biomass, plant biomass to herbivores, herbivores to carnivores, etc…
e.g. conversion of foods to animal biomass requires energy for metabolic processes to occur
it takes energy to maintain biomass organization
Resources restrain organisms’ rates of increase
LEIBIG’S LAW OF THE MINIMUM:
Distribution of a species is controlled by that environmental factor for which the organism has the lowest range of adaptability or control
E.g. No water => no human occupation (unless provided artificially) even if food IS somehow available.
Related: Numbers will decline with decrease in levels of required nutrients.
Leibig’s Law of the Minimum (graphic):
Distribution of a species is controlled by that environmental factor for which the organism has the lowest range of adaptability (how well can it do with low or no levels) or control (ability to acquire resource)
If you supplement that lowest factor, then the next lowest becomes limiting
E.g. Hierarchy of limiting factors in nutrition also depends on environment, lifestage, activity, reproduction
LAW OF TOLERANCE
No organism can live under every condition :
Geographical distribution is determined by upper and lower bounds of physical tolerance
Shelford 1913
Outside of these boundaries don’t find the organism;
Obvious example: no oxygen => no human habitation
Biological adaptation (e.g. body size to cold)
Humans: Cultural adaptation (e.g. clothing is a cultural adaptation that increases tolerance to cold environment)
Population numbers are limited by resources
CARRYING CAPACITY (K) = maximum population size of a
biological species that can be sustained by that specific environment.
LIMITING FACTOR & K: Change in level of resource results in change
of carrying capacity (individuals per square area)
REGULATING FACTOR: Change in level of factor changes vital rates (birth rate, death rate) as population density increases (e.g. death due to cholera or Covid-19 increases with population density)
Selection and adaptation
Selection tends to occur near the edges of tolerance or minimums
e.g. tolerance for starvation
Selection for ability to survive on less food to slow growth, to reduce reproductive rate, migrate out of area where food is scarce
Abiotic factors (density independent) and human adaptation
Many species wide adaptations clearly responses to abiotic environment
e.g. Temperature
e.g. body size, fur & underfur
UV Radiation
skin coloration
hair ?
body coverings
Body form and cold temperature
Bergmann’s Rule: Larger bodies (trunks) evolve in colder temperature
Why?
Produce our own heat
Require body temp near 37 degrees
Ambient equilibrium = 29 degrees
In cold temperatures need to conserve heat to maintain body
temperature
Lose heat from surface
Larger body has less surface area per volume for heat dissipation
Human body size and temperature
Local adaptation: Body size & temperature
Bergmann’s rule
- Body size of homeotherms increases with decreasing mean
temperature
Humans better adapted to tropical than to temperate or arctic environments
longer evolution in warm climates
Hot climate
The problem is excessive heat build-up core burns energy producing heat which must be dissipated hot environment -> little thermal gradient
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Adaptations
Large surface area : volume
Small trunk and elongated appendages
Higher surface area / volume ratio
Body form and climate
(English / cold temperate latitude) anthropologist Colin
Turnbull with Mbuti people from the
Ituri forest (hot, humid)
Reduced expression of Growth
Hormone Receptor
Many exceptions and complications
- Different ways to adapt
- Dry versus humid heat
- Diet and energy requirements
- Recent migrations
Is climate the only reason for body size and shape variation?
Allen’s rule: appendages & temperature
Length of appendages of mammals decreases with decreasing mean
temperature
Cultural adaptation to UV & heat
Layers of loose clothing (insulation) reduce exposure to UV and
reduce water loss
Summary
Patterns of adaptive responses to some abiotic selective pressures are relevant to some inter-population variations.
These adaptations must have occurred since dispersal out of Africa (within last ~70KYA)
The selective pressures result in clines of variation related to the environmental gradient of the relevant selective pressure
Body size, size of extremities, and skin colour demonstrate clinal variation correlated with environmental variation
These adaptations are specific applications of “laws” of ecology and biological adaptation that apply to most homeotherms
