Flashcards in CiE - End-of-Year Exam Revision Deck (18)
Describe 2 models to explain how multiple species coexist.
Either based on equilibrium or non-equilibrium.
INTERMEDIATE DISTURBANCE HYPOTHESIS
> Non-equilibrium model
- treats ecosystems as dynamic and evolving
> Disturbance prevents competitive exclusion and therefore doesn't allow for domination of K-selected sp
> Promotes diversity
> At a point between r- and k-selected sp. will be highest diversity and stability
- never constant, always changing
STORAGE EFFECT HYPOTHESIS
> Aren't synced, but are separated temporally
> Fluctuating environmental conditions will result in fluctuating reproduction rates
- I.e. Some years will be good for some species, and not others, and vice-versa
> sp. either need to have adults that are able to survive over poor years in order to reproduce when conditions are favourable, OR for short lived sp., they need to be able to store their genetic material to be able to recruit when conditions are favourable.
> that's what allows for multiple species to co-exist: fluctuating environmental conditions favouring some species over others;
- storage effect allows for sp to survive when conditions aren't favourable
Explain 2 mechanisms that can lead to ecological complexity
> Suppress abundance/alter behavior of one sp. level
> Releases next trophic level from predation/grazing changes
> Multiple interactions of cause-and-effect in ecosystems
- e.g. Darwin and cats in towns
- by adding effect of cats on mice and mice on bees you can measure observed effect
> Chain indirect effects
- sp. C changes the abundance of sp. A
- e.g. feral pigs and goats and vine on pacific island.
> Uneven distribution of concentration of variables in a landscape or population
- Multiple sp. of plants and animals (biological)
- Multiple terrain formations (geological)
- Multiple environmental characteristics (rainfall, T, wind)
> all these factors create different habitats which accomodate a greater amount of sp.
> Leading explanation - when organisms finely subdivide a landscape into uniquely suitable habitat
- More sp. can coexist without competition
- "niche partitioning"
Why are there so many types of fruits and dispersal patterns in plants?
> To overcome herbivory
> To maximise dispersal and therefore reproductive success
> Patterns of seed dispersal are determined by the dispersal mechanism
- gravity (apples)
- wind (many weed seeds)
- ballistic (explosive)
- water (something)
- animals (poop, horehound (fleece)
- serotinous (environmental stimulus; e.g. fire and Aus natives)
> Incr. in dispersal distance = incr. chance of seedling survival
- less predation, pathogens, fungi, competition
- these target [high] of seeds beneath adult trees (of the types that drop fruit/seeds using gravity)
> Plants can also change their fruit to adapt to a different/changed environment
- e.g. White Campion
- Changed fruit wall thickness and seed size after invading new territory with limited/no grazing pressure
Describe 3 hypotheses to explain why some species are aggressively invasive
RESOURCE GAPS EXPLOITED BY INVADER
> Newly opened gaps in resource use "allow" invasion; e.g.
- a change in land use that results in decreased abundance of native sp.
- introduction of new disturbance regime free up resources
- increased resource base (e.g. ag runoff, effluent)
- climate change
> This theory accepts "empty niche" idea
- assumes there are unused resources
- often the case in low diversity ecosystems
POORLY ADAPTED NATIVE SPECIES
> Especially in rapidly changing environment (e.g. climate change), invaders might be better adapted to habitats than endemic native sp.
- e.g. recent evolution of Mediterranean conditions in Aus has enabled some sp. to adapt better
- e.g. olives
- able to extract soil water at high negative MPa
- ecophysiological adaptions to avoid H2O loss
- leaves display vertically and are small, waxy, waxy, highly reflective, and have stomata only on one side
- root network is extensive and only grows in winter and summer when the water content is high.
ESCAPE FROM ENEMIES
> Introduced sp. have no known predators or parasites in new area
- Little evidence, but probably true if specialist herbivores or pathogens
- e.g. White Campion - a roadside ag. weed in N. US
- Transported in dry balast from Eur.
- No grazing pressure in new location
= decr. seed defense (fruit wall thickness)
= incr. seed mass - a direct measure of reproductive fitness
INCREASED REPRODUCTIVE CAPACITY
> More similar to r selected sp.
> Able to colonise areas quickly after disturbance
- Aus natives mostly K sp.
- Introduced sp. able to outcompete and become invasive
Define inducible and structural defenses, and explain the benefits and disadvantages.
> Co-evolution between plants and herbivores. plants evolve:
- STRUCTURAL DEFENSES
- permanent, constitutive defenses;
- toxins (e.g. tobacco and nicotine)
- thorns (e.g. raspberry cane)
- doesn't hinder growth - not a drain on resources
- allows for adaption by predator sp.
- e.g. goats being able to eat tin cans
- e.g. monarch butterfly sequestering toxins
- e.g. possums eat to toxic threshold, then go eat something else while their bodies process the toxin.
- INDUCIBLE DEFENSES
- perception of attack/herbivory triggers defense mechanism (synthesis of chemical or structure)
- e.g. radish releases glucosinolates when under attack by cabbage looper caterpillar which decreases pupation rates in the next generation.
- e.g. Camels and acacia (tough leaves)
- acacia makes leaves tough and spikey.
- somehow measures the height of the camel and only changes leaves below that height
- decr. chance of herbivore adapting to the plant defense
- community benefit
- talking trees (acacia example)
- DISADVANTAGE: high cost involved
- e.g. broadleaf dock, grazed by green dock beetle
- induces an increase in cell wall-bound peridoxase
- the reallocation of resources = decrease in new leaf and root growth
An increase in the likelihood of encountering herbivores = increase likelihood of investing resources in defense.
What is an 'evolutionary' vs 'climatic' relic?
> Once dominant, not able to compete with newer life forms.
> out competed and out evolved by evolutionary superior sp.
> not able to regain historic range, even if conditions changed
-e.g. magnolias and fast-growing trees
> More widely distributed in the past, may once again expand
- declined as a result of climate changes (glaciation, sea level rise, geologic separation due to plate tectonics)
> If favourable conditions returned, may be able to regain historic range
- e.g. Northofagus Antarctic Beech
- Used to occupy large area of Gondwana, now confined to confined to cool, wet locations - Tas, NZ, Chile
Using an example, explain the paradox of invasion
> Not really a paradox - easily explained
> Plants should thrive *best* in their natural environment (that they evolved in)
Paradox because many species that perform better in their new environment than in their native environment
e.g. Brushtail possum
- In Aus, declining
- In NZ, pest
New Lox =
- No predator/grazer
- Lack of pathogens
- Decr. defense
- Incr. breeding]=
What are some temporal effects on ecosystem functioning?
> Population responds to independent variable, but not right away
- i.e. abundant food on yr = incr. birth rates in the following yr and low food (= the opposite but even larger delayed response if animal has the ability to store fat)
- Also impacts predator/prey through delayed effect of incr/decr birth/death rates
Impact one sp. has on community development by prior arrival
> Inhibitory priority effect = decr. resources or space
- possum example
- pine/coniferous trees
> facultative priority effect = alter biotic conditions to increase suitability for future sp.
- mushrooms that can digest hydrocarbons
- pioneering sp. that can start cycling nutrients
Understanding priority effects helps devise cost-effective strategies to increase survival and persistance of certain sp.
> especially sp. of inferior competitive ability
- e.g. Forbs and Bunchgrasses
- Plant F -----> B = live together 3-4 yrs
- Plant B -----> F = no F survive
Explain 'indirect effect' and provide an example
> Multiple interactions of cause and effect in ecosystems
> Can't generalise behaviour of an animal and make assumptions
- e.g. feral pig and goat eradication on Pacific Is.
> Important for management of ecological systems
- imperitive to know what indirect effects may result from specific management options/actions
- e.g. corn grown in Nicaragua and introduction of widespread herbicide use
What is a niche?
> Where a sp. lives
> What it does (i.e. how it interacts with the local environment)
> What space it occupies in the landscape
> Within the environment:
= range of conditions, resource levels, and sp. diversity
- all affect reproduction/survival/growth
> what resources it uses
> what interactions it has
Compare niche concepts and describe how they're relevant to species distribution modelling
> "empty niche to be filled" or "cubby hole a sp. fits in to"
> determined by habitat characteristics and food types
> e.g. Spinifex Hopping Mouse and Saharan Jerboa
- occupy the same niche, pretty much
> doesn't consider sp. interactions
> assumes the niche is there regardless of whether the sp. is there or not.
POPULATION-PERSISTENCE NICHE (N-dimensional)
> focus on sp. of interest and
> multidimensional space of resources (e.g. light, nutrient, structure, etc) and availability to organisms (and use by them)
> divides niches into fundamental niches and realized niches
- fundamental = largest area where can persist with no competition or predation
- realized = actual area of fundamental niche actually occupied by a sp.
> a niche is a description of resource use
> sp. that are too similar cannot coexist
> similarity expressed as niche lox proximity vs niche width
- generalists have large niche width
ENVIRONMENTAL NICHE MODELLING
> enables sp. distribution modelling using elements from all 3 concepts to predict potential future sp. range, combining info from:
- overlaps of dundamental niches (population-persistence)
- lox with right characteristics and absent competitors (recess role)
- niche similarity between sp. (resource-utilisation)
- e.g. pygmy bluetongue lizard
Can grazing improve productivity?
> increaser plants overcompensate when defoliated
> avoid grazing as low to ground and can be unpalatable
> physiological mechanisms to recover from grazing
In a system where the dominant plant is palatable
- some grazing will decr. relative abundance
= decr. in population of dominant sp.
= incr. in system diversity
- also enables niche partitioning of competing sp.
Grazing changes soil composition
- e.g. in arid lands, destroys crusts, breaks down mosses
= incr. niche for dispersing seeds
= decr soil crust = incr. emergence
- source of OM (nutrients) and microbes
Grazing can keep plants in the most productive phase (phase 2)
- if change to reproduction, putting energy into creating seeds, not more biomass (which is what productivity is a measure of)
Describe the Latitudinal Biodiversity Gradient and global patterns of distribution of sp.
> Range size of new world birds was investigated
> Majority of sp. with smallest ranges lives @ 17deg. N of Eq.
- shouldn't have to travel far to find resources
> lies @ point of vegetation transition between grassland and mid-atlantic forests (thin band of rare and specialised habitat)
- not replicated outside of Americas
In Australia, there's no latitudinal pattern of distribution with eucalypts (only 6% of sp. cover > 1% of Aus)
- largest range size close to largest/widest region but not quite, as this latitude is not as habitable as others
- sp. richness doesn't follow pattern
- SW WA (biodiversity hotspot)
Higher latitude sp. must survive an incr. range of extremes.
Randing behaviours are dynamic and based on resource availability
- decr. resource = incr. range
What are the impacts of climate change on distribution, behaviour and phenology?
> change in sun/solar radiation
> incr. in temp and decr. in rainfall = further melt ice caps
= sea level rise (i.e. future warming most dramatic in Arctic)
> further drying of dry regions (e.g. Oz and Goyder's Line)
> Cool temp animals more (e.g. Cod and anglerfish in UK move N)
> Change in phenology:
- emergence of insects affects deciduous trees (leaf furl and fruiting), the arrival of birds to breeding grounds, and the dates of 1st breeding
- plants that require vernalisation to initiate flowering
cherries, cabbage, carrots, kale
> if break from phenology and breed at wrong time then decoupled from "right conditions" for later life stages
Link "propagule pressure" to small population conservation
> Also called "introduction effort"
> underlies the success of introduced sp. as it refers to *how many* of a sp. are introduced
> introduction of birds in NZ
- if introduced >100, they would be able to self-populate
> Critical in small population conservation
- sp. introduction in large numbers and consistant numbers = incr. chance of survival
- several factors are key:
- size and frequency of introduction
- pathway of introduction
- characteristics of sp involved
- rate of immigration
> Effective population size (number of males vs females)
> Inbreeding coefficient
> small populations succumb more easily to:
- environmental variation
- inverse density-dependence
> declining populations can be sustained through constant immigration (i.e. source population + sink population)
> a population is less likely to go extinct if individuals are spread spatially so adverse conditions in one lox (a 'sub-population') will not negatively affect individuals in another.
Explain how herbivore behaviour evolved to avoid toxic plant compounds.
How can animals take advantage of plant defenses to increase fitness?
Why do insects have specialised diets and not mammals?
Plant defense mechanisms:
> chemical compounds (tannins, toxins, allergens)
> morphological (tough leaves, spines/hairs/thorns, resin/latex production)
Non specialist herbivores
> consume toxic sp. to threshold, then move to new sp. and accumulate diff toxic compounds while metabolising old in liver
- e.g. possums in eucalypt forest
- "avoid effect of toxic compounds"
> take advantage of plant defenses to increase their own fitness
- e.g. Monarch butterfly larvae locate high pressure latex tubule in plants.
- if they consume the latex = glued mandibles
- so they make small cuts/incisions in the plant, drain the latex, and munch away
> aphid digestive tract adapted so incr. [carb] not present for long periods, therefore not absorbed at incr. rate
> Monarch butterfly fat tissue/cells
- re-allocate/accumulate toxins in wings = poison wings
> Tobacco leaf caterpillar
- sucks sugar and carbs from phloem
- too many carbs ---> special digestive system allows large amount H2O + sugars to circumvent digestive system
- therefore concentrated A.A. and *some* sugars go through
= very efficient absorption
* Increased generation interval of mammals vs. insects allows for insects to specialise and adapt
- can also clear toxins faster due to no liver
Describe the basic principles of Species area Relationships using the theory of island biogeography
SAR = correlation between species richness and habitat characteristics (larger and less isolated a habitat = incr. sp. richness)
> Other factors influencing SAR
- sp. pool of source population
- level of isolation
- diversity of habitat (heterogeneity)
THEORY OF ISLAND GEOGRAPHY
= # of sp. found on island is determined by the balance of immigration and extinction
> affected by *distance* from source of colonists (mainland)
> rate of extinction once sp. colonises is (SAR/curve/effect)
> balance of forces = equilibrium level of both sp. richness and rate of sp. change
*Isolation increases extinction as no 'source' population to 'rescue'
Island size also effect
- large size = more immigration