Lec 15 slides and reading Flashcards
Physiological ecology as a way of thinking about organisms
Can view an organism a library of information, bearing detailed sets of genetic info written in DNA
Necessary to direct the assembly of a complex organism
It’s heritable and connects that organism to other organisms in a family tree of relatedness
How environmental factors determine distribution and abundance
All organisms have restricted spatial distributions
-if environmental factors in a particular habitat are too harsh for a particular species, it won’t be able to persist there
Environmental factors classified in 2 ways: abiotic and biotic factors
abiotic and biotic factors
Abiotic factors are manifestations of the non-living, physio-chemical world, whereas biotic factors arise from the actions of other organism
abiotic factors divided into:
conditions and resources
resources
Resources are necessary physical entities that organisms use up and can be depleted
conditions
Conditions are physical states that can’t be depleted, such as temp or pH
limiting factors
Factors that are important in determining whether a species can or can’t persist in an area are called limiting factors
At the broadest possible level, the 2 factors that are most likely to limit the distributions of terrestrial species are temp (condition) and water (resource) → considered “the Big 2”
why is altitude considered a complex gradient
Altitude considered a complex gradient because many simpler factors vary with altitude in nature: temp, amount of precip, type of precip, partial pressure of oxygen, depth of winter snow
Any particular species is likely to be restricted to only a portion of an ecological gradient, if the factor that varies along the gradient is a …
limiting factor
-that portion constitutes the range of tolerance for that particular factor, and it can also be considered as defining part of the niche of that species
-range of tolerance classically graphed as curves that show how an organism’s ability to function changes along the gradient
-if the gradient is long enough, there’s usually a peak at some point, where the environ is optimal for the organism to THRIVE
death zones
At increasing distances from their optimum, organisms find the environment increasingly stressful
First, they become unable to grow well enough to reproduce, then they become unable to grow at all and finally they become unable to live → death zones
why is water important
Water is important because it affect the concentrations of chemical rxns, but especially because cells and tissue depend on membranes to compartmentalize chemical processes and reactants
Proper functioning depends on osmotic balance
If cells get too dry, the concentrations of dissolved salt increase
Chemical rxn are slowed and changed
If too much water enters cells, rxtnt gets diluted and fail to combine as needed
Organisms can also be in danger of overheating, overcooling, drying out and getting waterlogged
Environments typically contain a far broader range of physical conditions than the much narrower ranges of tolerance that characterize organisms (death zones)
Things tend to equilibrate
Objects, whether organisms or inanimate objects like rocks, will tend to reach the same temp as their environ.
In the hot sun, things heat up
In dry environ, objects will lose water and become saltier
Environments are much larger than organisms, so equilibration is asymmetrical
Generally, organisms are intrinsically vulnerable, environments are intrinsically implacable
homeostasis
They must be able to keep their internal states constant (or at least within narrow bounds), a process known as homeostasis (“staying the same”)
2 categories of homeostasis
thermoregulation (maintaining temp)
osmoregulation (maintaining saltiness)
Organisms vary hugely in their capabilities for thermoregulation and osmoregulation
Much of this depends on…
body size and shape
The most important aspect of body structure is the ratio of surface area to volume (SA/V)
Consider a tiny, aquatic, single celled Paramecium in a freshwater pond. Because it is so small, its SA/V ratio is high: any miniscule amount of heat that it could generate in its tiny body would almost instantly be sucked away by the overwhelming mass of water
active regulation
refers to the continuous and dynamic process of monitoring, adjusting, and controlling certain conditions, behaviors, or activities to achieve a desired outcome or maintain a specific standard
in biological systems, active regulation refers to how organisms maintain homeostasis (stable internal conditions) despite external changes
For example, the human body actively regulates temperature, blood pressure, and glucose levels
-mechanisms such as sweating, shivering, and the release of insulin are part of active regulation
The organisms most capable of homeostasis have _______ bodies and complicated metabolisms
large
warm-blooded animals exhibit very active regulation of heat balance to keep their body temperatures almost constant, despite great fluctuations in ambient temperature
cold blooded animals
In contrast, the “cold-blooded” animals (fish, amphibians, reptiles and virtually all invertebrates) tend to be thermoconformers whose body temperatures more closely track ambient temperatures
“homeothermy versus poikilothermy”
stresses the constancy of body temperature, as opposed to variability
“Endothermy versus ectothermy”
emphasizes that temperature is primarily determined by physiological processes acting within the body, as opposed to being determined by the external environment
conduction
Conduction is the direct transfer of heat between two bodies that are in contact
If there is a temperature differential, heat will flow from the warmer object to the cooler
Given enough time, the two objects will equilibrate at the same temperature
convection
Convection is heat transfer that is facilitated by a moving fluid—typically air or water. If you stand in an icy flowing stream, the cold water not only extracts heat from your feet in a conduction-like process, but the current sweeps the slightly heated water away, so local equilibration is minimal
Convective flows therefore tend to increase rates of heat transfer
Water is a much more effective medium for heat exchange than air is
true or false: radiative heat transfer involves molecules bashing into each other and transmitting their kinetic energy
false
applies only to conduction/convection
homeostasis and heat balance
Remember that the active vertebrates we are considering generate considerable amounts of heat from their internal metabolic functions, especially muscle contractions
Shivering is an effective way to increase internal heat production
In a cold environment, animals need to conserve that heat or generate more of it, but in a hot environment, they need to dump it or make less
The most basic adaptations—if not necessarily the most effective—for controlling these balances concern the size and shape of the animals
bergmann’s rule
If one examines a number of closely related homeothermic species that occur in habitats with different temperatures, there is a tendency for the species from cold environments to have larger body sizes
Because larger bodies translate to lower SA/V ratios, they retain heat better and lose less of it to their cold surroundings
In a tropical environment, an animal the size of a polar bear would have a hard time shedding heat, and tropical bears are gratifyingly small
allen’s rule
He claimed that animals from hotter environments had longer and thinner appendages: legs, tails, ears, sometimes horns or frills
That difference in shape will increase the surface area, given a constant volume
Rabbits are a group in which this trend is nicely shown
The comically large, almost paper-thin ears of rabbits are classic cases of maximizing surface area
Aside from affecting SA/V relationships in purely geometrical ways, extremities can be further specialized for dumping heat from the body core by managing blood circulation
how do rabbits follow allen’s rule
Rabbit ears are heavily vascularized, and the flow of blood to them is regulated.
Sphincter muscles around arterioles are especially effective in regulating how much blood is pumped into ears, for example
An overheated rabbit that needs to reduce its body temperature can pump hot blood to the ears, where the large surface area allows quick equilibration
Rabbits can also position their ears to increase or decrease heat exchange
Homeothermic vertebrates achieve insulation with…
layers of body fat, or as layers of fur or feathers
In the case of fur and feathers, the real insulation is provided by dead air spaces within the material
Countercurrent circulation in extremities
In a cold environment, that loss of heat would be a liability
Imagine a whale’s flipper. To fulfill its primary function—powerful swimming strokes—it must (1) stick out into the water, (2) have a large surface area, and (3) be thin
These mechanical constraints all make the flipper a terrible liability with respect to heat loss. However, this liability can be reduced by an arrangement of blood vessels called countercurrent circulation
This simply entails direct contact between the arteries that send warm blood out to the flipper and the veins that bring cooled blood back to the body
With these vessels closely appressed, heat exchange can occur between the arterial and the venous blood
This means that the cooled returning venous blood captures warmth from the outgoing arterial blood before that warmth can be lost to the environment
Instead, the returning venous blood carries that heat right back into the animal’s core
Furthermore, because the blood flows are going in opposite directions (countercurrent), there is a continuous temperature gradient between the two vessels (see schematic diagram in lecture slides)
Therefore, the transfer of heat continues along the entire appressed length of the paired vessels
evaporative cooling
Because of water’s great heat of evaporation, exposing moist surfaces to air flow is a very effective way to cool a body
Sweating works best with bare skin, so it is particularly effective for humans
Mammals that are mostly covered with fur, such as familiar cats and dogs, sweat from exposed skin such as paw pads
They also achieve evaporative cooling through panting, which draws air over wet surfaces of the tongue, pharynx, and lungs
Birds achieve most of their evaporative cooling through their respiratory system, which includes a system of air sacs that provides a more continuous flow, rather than the less efficient in-and-out airflow of mammals
Environments that would be dead zones for humans and many other animals are comfortable homes for species with appropriate …
adaptations
physiological ecology
-physiologists study how organisms acquire energy and nutrients and tolerate physical conditions
-ecologists study how organisms deal with their environ and how the environ limits where they live
-physiological ecology or “ecophysiology” is simply the study of physiology in the context of an organism’s ecology
ranges of tolerance limit..
distribution
maintenance of homeostasis requires energy and is often limited by …
constraints and tradeoffs
-e.g. homeotherms have to eat more
an organisms physiology reflects …
the climate and other conditions to which the organism is adapted
why do temperate animals in high latitudes have more variation
bc of tolerance
seasonal temp variation is ____ near the equator and ______ with latitude
low; increases
poikilotherms and heat balance
cold blooded animals that eat less (dont need to stay warm)
-lack physiological means to deviate from environ temp, their temps fluctuate
homeotherms and heat balance
mammals, birds
-must regulate heat balance to keep internal temp within a narrow range: many traits contribute
why do poikilotherm have LOWER energy requirements than homeotherms
maintaining a constant internal temp requires energy (they eat less+ dont need to eat to stay warm)
radiation
heat transfer by electromagnetic radiation
conduction
transfer by direct contact with substrate (e.g. feet lose heat to ground)
redistribution
circulatory system redistributes heat among body parts
-esp core to appendages
size and heat
-size matters to heat balance
-homeostasis and surface area:volume ratio
-volume provides the inertia
surface area determines…
equilibration rate
radius:1, SA/V:3 (smallest)
equilibrates quickly
-shed heat quicker
-better for hot environ
radius:3, SA/V:1 (biggest)
equilibrates most slowly
-shed heat slower
-retains heat
-better to
bergmann’s rule
homeotherms tend to be larger at higher latitudes (colder)
-low sa –> retain heat better
allen’s rule
homeotherms tend to have smaller appendages at higher, colder latitudes
e.g. big ears facilitate heat loss
how does countercurrent circulation to limbs conserve heat
-arteries and veins should be appressed in appendages to conserve heat; separated in appendages designed to shed heat
-countercurrent flow maintains gradient, so heat is always flowing from outgoing blood to incoming blood
example of a trade-off
skinny weasel in cold climates
-being long and thin makes weasels subject to thermal stresses (costly)
-but allows them to be better predators (beneficial)
-bc they are long and thin, we infer that the fitness gains of being a good hunter offset the fitness costs of an expensive metabolism
-if they can’t get enough prey, they can stay warm despite their heat-wasting shape
benefits outweigh the cons
2 reasons why natural selection produces deeply imperfect organisms
1) trade-offs
-being good at x may not necessarily imply being bad at y
2) constraints
-selection builds on whats already there, especially existing developmental programs
-more like tinkering
