biogeography & biodiversity Flashcards
& parasitism, herbivory
key factors shaping diversity
- location / isolation (for island sp)
- habitat size / area
effects of location/geography on biodiversity
grad in biodiversity associated with latitude -> these shaped by climate (water & sunlight)
examples:
-
tree diversity:
-> ~100 sp in 1 Ha of Malaysian forest
-> ~50 sp in all of W. Europe (2 million km²) -
ant diversity:
-> over 200 sp in Brazil
-> 73 sp in Iowa
-> 7 sp in Alaska
Climate is likely the key driver of latitudinal diversity gradients…
- ACTUAL EVAPOTRANSPIRATION
-> determined by solar radiation & water - POTENTIAL EVAPOTRANSPIRATION
-> measure of solar radiation independent of water availability)
One of the 1st general patterns of biodiversity described?
SPECIES-AREA relationship
-> lots of potential reasons
e.g. larger areas contain…
- ↑ habitat diversity
- support larger pops
- ↓ likelihood of local extinction
island equilib model
describes diversity as resulting from…
equilib between rates of sp gain (via immigration) & sp loss (via extinction)
herbivory (and herbivores)
- exploitative interaction: +/-
- +ve outcome for herbivore: food
- -ve outcome for plant/alga – loss of reproductive organs, food synthesis
- key diff from predation is that herbivory is usually not lethal -> eats part of a plant/alga
- diff herbivores generate diff effects
- herbivores are 1º consumers
herbivory: effects on plants
- depends on timing of attack relative to development (e.g. Plant age or leaf age)
-> if young more likely to be fatal - plant usually remains alive in short term
- effects dependent on response of plant
-
catastrophic grazing is rare (unless plants attacked early in development)
-> opportunity for plants to respond / plant defences to act
types of effects on plants that suffer herbivory
-
UNDERCOMPENSATION
-> grazed plants have lower fitness than ungrazed plants -
OVERCOMPENSATION
-> some grazed plants have GREATER fitness than their ungrazed: e.g. ↑ fruit & seed production
plant compensation
degree to which plants can tolerate grazing
fitness
organism’s ability to pass its genetic material to its offspring
-> can be measured in various ways, inc…
- no. fruits or seeds
- probability of survival
- growth rate
in overcompensation in grazed plants, how can they have a greater fitness than ungrazed?
- may evolve in plants where there is predictable amount of herbivory e.g. in path of herbivore migration
- keep dormant tips in reserve to be used after herbivory has occurred
- tradeoff: the cost is that…
-> plants have ↓ flowers
-> ↓ reproduction in absence of herbivory
COULD ALSO BE DUAL STRATEGIES…
- with low herbivory: plants are ↑ competitive and grow small no. of shoots rapidly
- with high herbivory: rapid growth
is less of an adv and it’s better to overcompensate and have lots of branching and flowering for higher fitness
defensive adaptations of plants
-
toxins & secretions
-> morphine & other alkaloids, digitoxin, agrostemmic acid -
spines & stings
-> num-num plant thorns occur at ↑ densities at heights where herbivores graze -
abscission (dropping) of leaves
-> leaf miner mortality much ↑ in leaves that have been shed
Some toxins are bad for herbivores but not toxic to humans.
give examples
valuable crops eg…
- curry
- rosemary
- cannabis
- tobacco
Constitutive defences
of plant
present before a herbivore attack (e.g. thorns)
Induced defences
of plant
take place only when attacks occur
example of mutualism against herbivores
acacias & ants
- plants provide refugia (hollow thorns) for ants
- ants attack & kill small herbivores & discourage large grazers (e.g. elephants)
BUT…
- in absence of herbivores: acacia stopped producing ant houses in hollow thorns & stopped excreting sweet nectar that bodyguard ants eat
adaptations of herbivores
Chemosensory apparatus
- chemical sensors on feet to identify toxic & most nutritious plants.
-> sense of smell e.g. goats
Digestive systems
- mutualists with cellulase activity
- multiple chambered stomachs
- coprophagy (eating faeces)
- grinding teeth, trunks, tongues, stylets (piercing mouth part)
symbiosis
- when 2+ sp live in direct & intimate contact
- interactions may be harmful, beneficial or neutral
parasitism
- where symbiont derives benefit from another organism (host)…
- to that organisms cost
- each parasite attacks few individs (rarely more than 2) during its life
- this intimacy distinguishes parasitism from true predators & grazers
parasites are starting to be conserved (conservation plans).
why?
- essential for healthy functioning communities
- major contributor to mortality and can impact abundance of organisms
- 5-10% of 450 parasite sp studied are committed to extinction by 2070 from climate-driven habitat loss
- up to 30% of parasitic worms committed to extinction
endoparasites
live within host’s body
eg. hookworm, tapeworm, liver fluke
ectoparasites
feed on external surface of
the host
eg. copepods, lice, ticks, fleas
parasitoids
one type of paratism
- Insects (usually small wasps) lay eggs inside host
- larvae develop inside living host, feeding on it & eventually killing it
- numerous eg.s, some developed as biological controls
parasitic plants
E.g. Rafflesia sp. (corpse flower, no stems, leaves or roots), and many Orchids
- plant that derives some / all nutritional requirements from another plant (holoparasitic)
- Rafflesia are holoparasitic
-> obligate parasite -> cannot complete life cycle without host
parasite life cycles are often complex.
give example and describe
5 steps
eg. blood fluke -> 2 free-living stages & 2 hosts
-> causes schistosomiasis
- mature flukes live in blood vessels of human intestine -> female fluke lives on males larger body
- flukes reproduce sexually in human host. Fertilised eggs exist host via faeces / urine
- if faeces / urine reaches water source: eggs develop into ciliated larvae -> larvae infect snails (intermed. host)
- asexual reproduction in snail => motile larva -> escapes snail
- larvae penetrate skin & blood vessels of humans exposed to water contaminated with fluke larvae
schistosomiasis
blood fluke causes this
caused by parasitic flatworms (schistosomes)
- urinary tract / intestines may be infected
- symptoms inc abdominal pain, diarrhea, bloody stool / blood in urine
with every required transmission to new host, parasite risks not infecting the next host & dying before reproducing.
why do parasites often have complex life cycles?
experiement done with 973 parasite sp
- found that parasite growth & reproduction highest in large hosts – parasite fecundity (fertility) higher as they can grow bigger
- but large hosts typically only accessible via small intermed. hosts
-> small hosts facilitate transmission as more abundant - so complex life cycles arise because best hosts for growth & transmission are not the same
(to get to big host: need to go to small host first for improved transmission)
Parasites can alter behaviour of hosts.
example?
Succinea snails & Leucochloridium paradoxum (parasite)
- L. paradoxum is endoparasitic flatworm of both Succinea snails & various birds, inc crows, sparrows & finches
- when on snail host: it needs to get to bird host. To do this…
-> causes drastic deformity in its intermed. host, (Succinea snail)
-> also provokes behavioral changes that ↑ suicidal tendencies in snail - parasite causes both snail’s tentacles to be occupied by a broodsac -> mimics appearance of insect larva e.g. caterpillar, ↑ likelihood snail will be eaten by parasite’s next host: birds
what are the suicidal tendencies shown by Succinea snail after parasite?
- snail more likely to stay in well lit places
- sits on higher vegetation
- more mobile
mutualism
interaction that benefits both parties
eg…
- Mycorrhizae & plants (nutrient exchange)
- Cellulose digesting microbes
- Leguminous plants
mutualism in Microbes
- in hindgut of a termite
- break down cellulose into more easily digested sugars & short-chain fatty acids
mutualism in Mycorrhizas
^beneficial fungi growing in association with plant roots
exist by taking sugars from plants ‘in exchange’ for moisture & nutrients gathered from soil by fungal strands
mutualism in Rhizobium
^genus of Gram-negative soil bacteria that fix nitrogen
- form endosymbiotic nitrogen-fixing association with roots of legumes & other flowering plants
- these bacteria colonise roots of leguminous plants that in response produce set of new organs called ‘nodules’ on their roots
key processes driving community dynamics
- competition
- predation
- herbivory
- symbiosis
- facilitation
most important ecological relationships on earth
Plants: nitrogen fixing, nutrient uptake
Corals: largest biological structures on earth
Madagascar Orchid sp & Hawk
moths mutualism
- moths enormous tongue can uniquely reach bottom of nectar tubes of Madagascan star orchid
-
+ve for moth:
-> if insect is only one that can access nectar it is guaranteed food others are denied -
+ve for orchid:
-> further ↓ risk of misdelivered pollen and can cut back on its investments
Cnidaria & algae
mutualism
- host coral gets energy from algal p/s
- algae get nutrients (N / a.a) from host
Mutualisms are susceptible to exploitation – each sp could gain more & give less.
give examples
- moths can chew into nectaries and gain food without pollinating Orchid - ‘nectar robbers’
- Cnidarians enslave their algae massively ↓ growth & ‘grabbing’ up to 95% of photosynthetic production
commensalism
- interaction that benefits 1 sp
- but neither harms nor helps other
commenalism example
Atlantic puffin
-> these puffins use burrows for nesting that were made by rabbits
facilitation
Like mutualism (but without direct contact) & typically involves plants
eg. Chondrus crispus:
- suffers desiccation at low tide
- survival ↑ in presence of fucoids, since canopy provides shelter
3 levels of biological diversity
- within sp
- within community/ecosystem
- within landscape – how diff are communities in sp composition?
landscape diversity
- ⍺ diversity – sp diversity in location / habitat patch
- β diversity -> how diff sp composition is among locations
- ɣ – species diversity at landscape level
Biophilia / love of nature
what does it lead to?
- biased towards ‘charismatic’ sp
- might be seen as a luxury, not necessity
why preserve biodiversity?
utilitarian
utilitarian: useful to humans, now / in future
- sources of genetic diversity for crop breeding
- new medicines
- ecosystem services in agriculture
-> e.g. pollination, pest control - carbon sequestration (capture and storage)
-> ecosystem functioning: we depend on local & global ecosystem processes
^more diverse ecosystems function better
