Human Ecology I

Question 1

Human Ecology 1: Roadmap

Answer 1

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

Question 2

What is ecology?

Answer 2

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

Question 2

Review: Natural selection (= individual selection)

Answer 2

“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?

Question 2

What is human ecology?

Answer 2

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.

Question 3

Adaptation (across generations)

Answer 3

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.

Question 3

Acclimation

Answer 3

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.

Question 4

Ecological processes: interface of humans with environment

Answer 4

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)

Question 4

Adaptation (genetic)

Answer 4

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)

Question 4

Summary: Types and examples of genetic adaptation

Answer 4

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

Question 4

Ecology & Adaptation

Answer 4

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

Question 5

Responses to the environment

Answer 5

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

Question 5

Aclimatization

Answer 5

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

Answer 6

Question 7

Population-specificPopulation-specific

Answer 7

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

Answer 8

Answer 8

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.

Answer 8

Answer 8

Answer 9

Answer 10

Answer 11

Question 11

A history of responses to environments

Answer 11

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)

Question 12

Recap

Answer 12

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.

Question 13

A history of responses to environments

Answer 13

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)

Answer 14

Question 15

Ecology 2: Roadmap

Answer 15

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

Question 16

Survival requires the transformation of energy and use of energy

Answer 16

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

Question 16

Physics and Ecology

Answer 16

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

Answer 16

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

Answer 17

Question 18

Resources restrain organisms’ rates of increase

Answer 18

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.

Question 19

Leibig’s Law of the Minimum (graphic):

Answer 19

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

Question 20

E.g. Hierarchy of limiting factors in nutrition also depends on environment, lifestage, activity, reproduction

Answer 20

Question 21

LAW OF TOLERANCE

Answer 21

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)

Question 21

Population numbers are limited by resources

Answer 21

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)

Question 22

Selection and adaptation

Answer 22

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

Question 22

Abiotic factors (density independent) and human adaptation

Answer 22

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

Answer 23

Question 23

Body form and cold temperature

Answer 23

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

Question 23

Human body size and temperature

Answer 23

Question 23

Local adaptation: Body size & temperature

Answer 23

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

Question 23

Hot climate

Answer 23

The problem is excessive heat build-up core burns energy producing heat which must be dissipated hot environment -> little thermal gradient

You don’t have any content yet.
Adaptations

Large surface area : volume

Small trunk and elongated appendages

Higher surface area / volume ratio

Question 24

Body form and climate

Answer 24

(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?

Question 25

Allen’s rule: appendages & temperature

Answer 25

Length of appendages of mammals decreases with decreasing mean
temperature

Answer 26

Answer 26

Answer 26

Answer 27

Answer 28

Question 28

Cultural adaptation to UV & heat

Answer 28

Layers of loose clothing (insulation) reduce exposure to UV and

reduce water loss

Question 29

Summary

Answer 29

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