Ecology Flashcards
what is ecology?
the science of biodiversity:
- how organisms interact with each other and with their environment
- distribution and abundance of species
- structure and function of ecosystems
how many species are there?
globally, too many to count. many (>85% are still unknown to science). one estimate, extrapolated from rates at which new taxa are described is 8.7 million (just eukaryotes)
is biodiversity equally distributed across the tree of life?
no, 70-90% of species are bacteria
define a populations
all the individuals of the same species in one place at one time
define an ecological community
all the species living together in one place at one time
define an ecosystem
all the species plus the non-living environment
why do we care about species range?
- to understand where plants and animals can grow because they give us food, clothing, wood, medicine, etc
- predict what will happen to biodiversity as the climate changes
- predict how biodiversity will respond to habitat destruction, pollution, invasive species, etc
- to understand disease risk of microbes
what determines where species live?
- dispersal
- abiotic conditions: climate, nutrients
- species interactions: competition, predation, mutualism
what limits a species’ range?
- dispersal
- climactic or other inexhaustible conditions, eg temperature/salinity
- food or other exhaustible resources, eg nutrients/space
- species interactions eg competition/predation/mutualism
the sixth extinction
- ongoing mass extinction, mainly as a result of human activities
- 32% of known vertebrate species (8,851/27,600 species) are decreasing in population size or range
- North American birds have declined in abundance by 29% since 1970
Margulis
Lynn Margulis was an American biologist whose serial endosymbiotic theory of eukaryotic cell development revolutionized the modern concept of how life arose on Earth.
Malthus
English economist and demographer who is best known for his theory that population growth will always tend to outrun the food supply.
Draw and describe a general graph for the performance of species against an environmental gradient
label:
- lethal zones
- where growth occurs
- where reproduction occurs
- where survival occurs
species have ranges of tolerance along environmental gradients
define the ecological niche
- the combination of physiological tolerances and resource requirements of a species
- more casually, a species’ place in the world - what climate it prefers what it eats, etc
draw a graph and describe the Hutchinsonian niche
the niche is an ‘n-dimensional hypervolume’ shaped by the environmental conditions under which a species can ‘exist indefinitely’. Each axis is an ecological factor important to the species being considered
factors determining biomes
- temperature is mostly a function of latitude
- higher latitudes colder; seasonality a function of temperature (summer-winter)
- lower latitudes warmer; seasonality a function of rainfall (dry-wet season)
- rainfall mostly depends on atmospheric circulation, offshore ocean currents, rain shadows
Intertropical convergence
- shows a line of rain clouds across the pacific
- ITCZ shifts seasonally, producing rainy and dry seasons in some parts of the tropics
how does the ITCZ form?
When the northeast trade winds from the Northern Hemisphere and the southeast winds from the Southern Hemisphere come together, it forces the air up into the atmosphere, forming the ITCZ.
Coriolis effect
the earth’s rotation deflects winds: objects (including hurricanes) appear to be deflected eastwards as they move away from the equator and deflected westwards as they move towards the equator
general trends of terrestrial vegetation with climatic variables
- vegetation growth (primary productivity) increases with moisture and temperature
- vegetation stature also increases so region with certain combinations of moisture and temperature develop predictable, characteristic types of vegetation (biomes)
- seasonality is secondarily important
draw a Whittaker’s diagram
—– mostly determines terrestrial biomes
latitude
changes in temperature within basic latitudinal belts
land changes temperature more readily than water; maritime climates are moderate, continental climates are extreme; oceans provide thermal inertia
changes in precipitation within basic latitudinal belts
- evaporation high from warm bodies of water, low from cold
- prevailing winds
- orographic precipitation (air forced up mountainsides undergoes cooling, precipitates on upper windward slopes)
- rain shadows created on leeward slopes of mountain ranges
- seasonality of moisture also important
leeward slope
slopes that are oriented away from the wind
draw diagram of orographic precipitation
latitudinal patterns are complicated by
the distribution of landmasses
how do ocean currents affect precipitation?
driest deserts occur inland of cold-water upwellings as cold water -> dry air
when would animals’ geographical ranges not correspond to biomes (i.e. limited by climate or vegetation)
- transcend biomes (ecological versatility, super generalists)
- not at limits because of recent history (eg limited dispersal)
- limited by other organisms
describe ecological niche modelling
- also called species distribution modelling
- uses data from a species’ present distribution to predict where a species can live
- usually relies on climate data; more rarely on other niche axes, such as resources
what is ecological niche modelling useful for modelling for?
- biological invasions
- how species’ ranges may shift as climate changes
- spread of vector-borne diseases
describe Dengue
a virus vectored by Aedes mosquitoes
observed range shifts
- estimated that species are moving polewards
- although many factors influence a species’ range, there is considerable evidence that numerous species are moving polewards to track recent changes in climate
how are ranges of tolerance related to homeostasis?
reactions occur (enzymes function) best at optimum temperature and osmotic conditions where fitness is maximised.
what does an animal’s physiology reflect?
the climate and other conditions to which the organism is adapted
compare the tolerance of temperate animals to tropical animals?
- temperate animals withstand colder temperatures than tropical animals
- temperate animals also tolerate a wider range of temperatures than tropical animals
trends in seasonal temperature variation
low near the equator and increases with latitude
heat balance in poikilotherms
most reptiles, amphibians, fish, invertebrates
- lack physiological means to deviate from environmental temperature (although they use behavioural means): their temperatures fluctuate
heat balance in homeotherms
must regulate heat balance to keep internal temperature within a narrow range: many traits contribute to this
why do poikilotherms have lower energy requirements than similarly sized homeotherms?
maintaining a constant internal temperature requires energy
list the 5 modes of heat gain or loss
radiation
conduction
convection
evaporation
redistribution
radiation
heat transfer by electromagnetic radiation
conduction
transfer by direct contact with substrate (eg feet lose heat to ground)
convection
heat transfer mediated by moving fluid (usually air or water)
evaporation
efficient cooling from wet surfaces
redistribution
circulatory system redistributes heat among body parts, esp. core to appendages
how does size matter to heat balance?
- surface area determines equilibration rate
- volume provides the inertia
draw a diagram for radius vs SA:V and equilibrium
Bergmann’s rule
homeotherms tend to be larger at higher latitudes (colder)
if a sphere has the smallest SA:V, why aren’t homethoerms always spheres in cold climates?
- sometimes SA is needed for function
- sometimes particular shapes are needed for function
- tradeoffs and adaptive compromises
who has the maximum SA:V ratio?
Chrysopelea gliding snake, Borneo; restricted to warm tropics
who has the minimum SA:V ratio?
American Pika, Ochotona princeps: alpine tundra rabbit; restricted to cold habitats; spherical shape, reduced ears for a rabbit
Allen’s rule
homeotherms tend to have smaller appendages at higher, colder latitudes
what other factors matter other than shape and size?
- insulation
- convective cooling enhanced by vascularisation
- evaporative cooling
- countercurrent circulation to limbs conserves heat
describe how countercurrent circulation to limbs conserves 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
draw a diagram for countercurrent circulation
how is the skinny weasel in cold climates an example of a trade-off?
- being long and thin makes weasels subjects to thermal stresses (costly) but allows them to be better predators (beneficial)
- because 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 get enough prey they can stay warm despite their heat-wasting shape
two reasons why natural selection produces deeply imperfect organisms
- tradeoffs: being good at x may necessarily imply being bad at y
- constraints: selection builds on what is already there, especially existing developmental programs.
anther
bears pollen
stigma
receives pollen
why is physiological ecology different for plants?
- sessile, with little scope for behaviour; animals can escape adverse conditions, but plants must tolerate them
- autotrophic; they make their own food through photosynthesis
- all plants need the same few things to grow; light, CO2, water, and soil nutrients (esp NPK)
describe photosynthesis
CO2 + H2O –(light)–> carbohydrate + O2
- plants must bring together CO2, water, and light in functioning photosynthetic tissues
- enzymes also require a certain temperature
- for growth, plants have to acquire more carbon through photosynthesis than they lose through respiration; carbon balance is thus key
Net Primary Productivity (NPP)
C gained via photosynthesis - C lost via respiration
what happens in synchrony with photosynthesis?
- photosynthetic (green) structures are usually leaves (but can be stems)
- plants take in CO2 through stomata
- but plants also transpire; they lost water through stomata
how do photosynthetic structures embody adaptation to environmental stresses?
- leaf size and shape: SA:V ratio important
costs and benefits of large leaf SA
- benefits: good fro harvesting light, CO2
- costs: bad for overheating, water loss by transpiration through stomata
why and how have plants evolved to overcome the shortcomings of C3 photosynthesis?
- most plants fix carbon by C3 photosynthesis:
- rubisco is the enzyme that accepts CO2
- but at high temperatures, rubisco often captures O2 instead of CO2, which is bad for plants (photorespiration) - some plants have evolved:
- C4 photosynthesis: the enzyme PEP carboxylase first accepts CO2, reducing photorespiration
- CAM photosynthesis: plants close stomata during the day to reduce water loss, open stomata at night to let in CO2; photosynthesis still needs light, so they store CO2 as malate until daytime
how do plants with large leaves combat overheating?
- growing in shady habitats
- evaporative cooling by opening stomata
evaporative cooling needs plentiful water, which is not always available. Plants with large leaves combat water loss by:
closing stomata
fundamental trade-off between water conservation and rapid growth
- closing stomata shuts off all gas exchange, including CO2 input, so photosynthesis shuts down.
- the plant stops growing and risks overheating and tissue damage
in what plants are the consequences of the water conservation/growth trade-off most obvious?
desert plants
Palo Verde (Parkinsonia sp)
= green stick
- microphylly
- photosynthetic bark on trunks and branches makes up for this
- can grow without incurring heat load and water loss through leaves
- deciduous tree in response to drought (drops leaves)
leaves in tropical rainforests vs deserts
- tropical rainforests: warm and wet
- leaves very big
- deserts: hot and dry
- leaves very tiny
this is because rainfall is abundant in tropical rainforests, so plants can afford to have very big leaves and lots of transpiration
Santa RIta prickly pear (Opuntia Santa-rita)
Microphylly taken to extremes: no leaves
Saguaro cactus (Carnegiea gigantea)
restricted to Sonoran desert and adapted to episodic rains
- grows to 15m, 200yr, 5+ tonnes
- CAM photosynthesis
- extensive, shallow roots
- accordion-pleated trunk allows expansion
- can absorb 800L water from one storm, use it gradually for growth
describe cactus roots
extensive but shallow
- when it rains in the desert, the water moistens just the top few cm of soil but never penetrates any further
describe tropical tree roots
extensive but shallow
- have a shallow layer of nutrient-rich soil due to rain leaching
- extensive, shallow roots are an adaptation to acquire scarce nutrients (phosphorous, nitrogen, etc)
Root foraging
plants grow their roots in soils where nutrients are abundant
Rebecca Doyle and Legume species (Medicago truncatula):
split root experiment
- low N vs high N
- good vs bad NF bacteria
- legumes forage for both soil nitrogen and nitrogen-fixing bacteria
- legume roots grow larger in more nitrogen and make more nodules with good bacteria
can plants evade stress through behaviour?
deciduous habit:
- dropping leaves during dry or cold seasons reduces water stress and tissue damage
how does leaf shape influence gas exchange?
through laminar vs turbulent air flow over surfaces
- laminar: airflow unimpeded, moves in smooth fashion over a surface
- causes stagnant layer of air called a boundary layer to build up, preventing gas exchange
morphological plasticityL sun and shade leaves from one red oak tree
shade leaf: smooth surface, no bumps
- more laminar flow, less cooling
sun leaf: bumpy leaf
- more turbulence, better cooling
Monstera deliciosa
- dissected outlines cause turbulent air flow (sun leaf)
- fewer holes in shade leaves to promote laminar flow
recursive digression
convective cooling aided by turbulence
- small snow bunny has smooth surface to promote laminar air flow and keep it warm
what type of evolution are cacti an example of?
convergent
can plants in rainforests be water stressed?
yes, if they’re epiphytes
what are epiphytes?
plants than grow on trees, so they aren’t able to put their roots into the soil, leading to water stress and nutrient shortages
- some cacti grow epiphytically on trees
population size symbol
N
population density symbol
N/area
why do we care about understanding population size, N?
- natural resources management (eg size of fish stocks in the ocean, abundance of outbreaking insect pests in forests)
- conservation: population decline of a species
- health: monitoring populations of viruses or bacteria in humans
- understanding and predicting human population growth
- basic science question of what limits population growth
Population declines in Myotis lucifugous bats due to white nose syndrome (WNS)
- novel pathogen (fungus) emerged in bat population, causing a disease caused white nosed syndrome and really high mortality.
- steep decline in no of over-wintering bats
HIV population dynamics in humans - draw graph of CD4 cells over time
Malthus’ essay on population growth
in 1798, Malthus published an essay on the principle of population, arguing that the human population cannot grow faster than food production
Paul Ehlrich
published The Population Bomb, arguing that explosive growth in the human population would have catastrophic social and environmental consequences
how is the human population expected to change in the future?
demographers project that human population is soon going to peak, then fall dramatically (depopulation)
goals of most population models
- predict the trajectory of population growth through time, i.e. N as a function of t
- how many individuals are in the population now? Nt
- how many individuals are in the population one step later? N(t+1)
- so the general model is N(t+1) = fN(f)
- challenge: choosing simple but realistic parameters for f
when using differential equations, time steps are
infinitesimally small: use concept of limits and calculus; growth is smooth; best suited for species with continuous reproduction
when using difference equations, time steps are
discrete units (days, years, etc); use iterated recursion equations; growth is stepwise and bumpy; best suited for episodic reproduction
two types of time step approaches
continuous-time and discrete-time
how do we pick between the two time-step approaches?
different organisms might be better fit by one or the other
simple bookkeeping model: how can N change from Nt to Nt+1
D = number who die during one time step
B = number born during one time step
E - number who emigrate during one time step
I = number who immigrate during one time step
Nt+1 = Nt - D + B - E + 1
what variables can we consider to be equivalent?
- birth and immigration (ie individuals added to the population)
- death and emigration (ie individuals that disappear from the population)
geometric growth model
- assume no immigration or emigration
- treat birth and death during one time step as per capita rates that are fixed constants
- then, population changes by a constant factor each time step: N(t+1) = λNt
- λ is a multiplicative factor by which population changes over one time unit = ‘finite rate of increase’
- λ = Nt+1/Nt
if λ>1,
birth exceed deaths and population grows
if λ<1
deaths exceed births and population shrinks
N1 =
λN0
N2 =
λN1 = λλN0
N3 =
λN2 = λλN1 = λλλN0
so how can geometric growth be generalised
Nt = N0λ^t
exponential growth
- instantaneous, fixed per-capita rates of birth and death (b and d)
- instantaneous, per-capita rate of population change = b-d=r (a constant)
- r = intrinsic rate of increase
- differential equation is dN/dt = rN
- this model is exponential growth
draw a table comparing discrete-time and continuous time growth models
find the relationship between r and λ
lnλ=r
regardless of which model is adopted, the important consequence is the same
- in both models, the growth rate (λ or r) is a constant that simply reflects biology
- but a constant positive growth rate produces a population growth size that is not constant, but rather exploding in an exponential way
all species…
- have the potential for positive population growth under good conditions (λ>1.0, births exceed deaths)
- have the potential for negative population growth under bad conditions (λ<1.0, deaths exceed births)
- but no species has ever sustained λ>1 or λ<1 for a long period
why is exponential growth a bad model of reality over the long term?
- some factors use tend to keep populations from exploding or going extinct
- two kinds of factors may be acting: density dependent regulation (growth depends on N) or density-independent reduction
how can we model the classically, density-dependent growth?
the logistic equation; an exponential growth with a new term added for brakes
dN/dt = rN(1-N/k)
use bacteria as an example of two types of growth
The logistic braking term models… (draw graph)
the simplest form of density dependence
K
carrying capacity of the environment
logistic trajectories are truly
S-shaped only when
starting from low numbers
label an N vs t graph
logistic model pros
- Mathematically tractable model of intraspecific competition for resources
- Simple (only one extra parameter, K, beyond exponential)
- Can be expanded to consider multispecies competition
logistic podel cons
- Too simple: specifies one particular kind of
density dependence - Always a gradual approach to carrying
capacity - In reality, density-dependence is likely
to be non-linear, may see overshoots of K
possible ways to add more complexity or reality to exponential or growth models
- different forms of density dependence (allee effects)
- time lags
- incorporate species interactions (eg effects of competitors, predators, mutualists)
per capita growth rate is fastest when… what is an exception to this?
population is near zero; sometimes more density may be beneficial
what are Allee effects?
negative effects of low density, arising from social benefits such as mate finding, group living, group defence
meerkats
cooperate to avoid predators and rear young, so their populations require a minimum population density to grow
when Allee effects are in force
- populations may fluctuate between carrying capacity, K, and another, lower limit
- dropping below the lower limit goes to extinction
- very important in conservation
age-structured populations
- exponential and logistic models of population growth treat all individuals in a population the same
- but in real populations, not all individuals have the same probability of giving birth or dying
- fecundity and survivorship depend on age
- how these depend on age varies among species; species have different life history strategies
key components of a life history strategy include
lifespan, the timing of reproduction, number of offspring, and parental investment in offspring
typical life history for many plant and animals
- start life at small size
- grow for a period without reproducing (for resource accumulation)
- when have enough resources, become mature, start spending resources on reproduction
- organisms show various lifestyles after sexual maturity
- some expend all resources at once, see spread them out
- need to consider age structure of population to better predict population trajectories
elephants
low fecundity
long lifespan
late 1st reproduction
big investment in each individual offspring
pika
high fecundity
medium lifespan
fast first reproduction (within 1st year of life)
1-13 babies per reproduction cycle
salmon
very high fecundity
medium lifespan
late first reproduction
return to natal rivers at end of lives to have offspring then die right after
female can lay 1000s of eggs when she spawns
variation in fecundity and survivorship with age is summarised by
life tables of age-specific rates
life tables have important implications for
- evolution of life histories
- conservation of populations
- understanding the changing structure of human populations (human demography)
age-sex pyramid
males left, females right, height of bar Indicates how many individuals there are of that population
demographic transition undergone in Canada
pyramidal shape -> stable age structure with similar number at each age class
