Week 8: Island Biogeography

Question 1

character displacement (*)

Answer 1

evolutionary divergency of a character shared by similar species when their ranges overlap

Question 2

ecological release (*)

Answer 2

tendency of a population in a species-poor environments to occupy a broader range of their fundamental niche

Question 3

island syndrome

Answer 3

• COMMUNITY LEVEL: biotas depauperate; ecological interactions simplified/atypical; large/isolated/old islands are often hotspots of speciation, diversity, endemicity
• POPULATION LEVEL: demographic and ecological release, expand their niches
• INDIVIDUAL LEVEL: changes in body size; defenses against predators; increase tameness; woodiness in herbaceous plants; lost or highly reduced dispersal capacities

Question 4

species abundance relationship (SAD)

Answer 4

Relative abundances of species often fit a lognormal (bell-curve) distribution because: only few species are extremeley common, most are rare. And, as progressively larger areas are sample, you get more individuals and more species.

Question 5

species area relationship

Answer 5

species diversity…
- increases with area (species area relationship)
- increases less rapidly for larger islands
- mathematical generalization

Question 6

how species abundance distribution (SAD) and species area relationship are linked

Answer 6

Isolated islands have fewer species per unit area; slope of species-area relationship is much steeper for isolated islands than single large landmass (if species becomes too rare, it becomes extinct; can’t be sustained by exchange between local areas)

Question 7

species isolation relationship

Answer 7

species diversity decreases with isolation
(relationship is less clear)

Question 8

equilibrium and turnover

Answer 8

• equilibrium dynamic
• relative turnover rates (immigrators replacing species becoming extinct) tend to be lower for organisms with longer generation times

Question 9

importance of history of islands

Answer 9

• if fragments (broken off from mainland): get relaxation and paleo-endemism
• if formed de novo: get colonization and adaptive radiation

Question 10

equilibrium theory of island biogegraphy (ETIB)

Answer 10

Equilibrium between opposing rates of colonization (immigration) and extinction.
- equilibrium stable at point of intersection of curves
- equilibrium is dynamic because species turnover remains above zero as species new to the island continue to replace those that go extinct

Question 11

assumptions of ETIB

Answer 11

• ETIP is a neutral theory (differences between members of an ecological community is irrelevant to their success) –> point is to find a minimal but common set of processess that can satisfactorily explain observed phenomena.

(1) Area of an island affects extinction rate only – greater area allows more individuals to persist
(2) Isolation of an island affects the immigration rate only – rate decreases with isolation
(3) Does not consider speciation

Question 12

challenges to ETIB (target effect, rescue effect, speciation)

Answer 12

(1) Target effect: area affects not just extinction, but also colonization – larger islands provide larger targets to colonists
(2) Rescue effect: distance affects not just immigration, but also extinction rates – near islands have immigration that reduces chance of extinction
(3) on very isolated islands, speciation can out-pace immigration

Question 13

speciation and endemicity on islands

Answer 13

more remote islands = less frequent immigration = lower gene flow from mainland = hotspot of endemicity

Question 14

radiation zone

Answer 14

near the outer limit of the dispersal range of a given taxon; speciation within an archipelago can outrun immigration

Question 15

adaptive radiation (??)

Answer 15

–

Question 16

nonadaptive radiation (??)

Answer 16

related ecologically similar species that are allopatric or parapatric replacements of one another

Question 17

endemicity related to island area and age

Answer 17

(a) Area – effects of area on total resources; habitat diversity increases with island area, so more niches and barriers to gene flow (mountains, rivers); larger islands = larger populations = persist longer = in situ speciation
(b) Threshold area – minimum area below which the island is too small to produce endemics (due to resource requirements)
(c) Age – speciation takes time

Question 18

taxon cycles & evolutionary traps

Answer 18

driven by colonization of generalized species which evolves to become more specialized.

Stage I: widespread, undifferentiated species colonized from mainland.
Stage II: widespread form with well-differentiated subspecies on different islands.
Stage III: species with well-differentiated subspecies on only a few islands.
Stage IV: narrowly endemic species

Question 19

community assembly hypothesis

Answer 19

nonrandom patterns in the structure of communities and biotas.

Question 20

nestedness

Answer 20

• islands in the Atlantic and Pacific Oceans tend to form regular subsets of mainland biota
• disrupted by evolution/adaptive radiation
• selective immigration

Question 21

relict pattern

Answer 21

capacity to persist, given limited insular resources, may differ predictably among species; orderly loss of species

Question 22

alpha diversity

Answer 22

local diversity

Question 23

beta diversity

Answer 23

turnover diversity: distinct species

Question 24

niche conservatism

Answer 24

tendency of species to retain ancestral ecological characters

Question 25

organisms in a community may be:

(a) Phylogenetically and phenotypically clustered ()
(b) Phylogenetically and phenotypically over-dispersed ()
(c) Phylogenetically clustered and phenotypically over-dispersed (*)
(d) Phylogenetically over-dispersed and phenotypically clustered

Answer 25

(a) due to environmental filtering. species in each community are all closely related (phylogenetically clustered) and exploit the same niche (phenotypically clustered).

(b) due to how species interactions/competition shape species composition in the community. Species in each community are NOT each other’s closest relatives (phylogenetically overdispersed) and exploit different niches (phenotypically overdispersed)

(c) due to evolutionary change in traits associated with (for ex) adaptive radiation. species in each community are each other’s closest relatives (phylogenetically clustered) yet exploit different niches (phenotypically overdispersed); this can happen when close relatives come together and diverge through character displacement.

(d) due to extreme environmental filtering. species in each community are NOT each others closest relatives (phenotypically over-dispersed) yet exploit the same niche (phenotypically clustered). Not common, but could arise from filtering.

Question 26

convergent evolution

Answer 26

distantly related organisms may evolve similar adaptatioins to occupy similar niches.

can happen at many levels: marsupials vs placentals, anolis lizards on different islands, cichlids in different lakes

*repeated evolution of ecomorphs

Question 27

loss of dispersal

Answer 27

derived insular flightlessness associated with: loss of predators, energy conservation, loss to gene pool. currently high levels of extinction

Question 28

convergence of lineages (*)

Answer 28

–

Question 29

body size: island rule

Answer 29

Individuals tend towards size extremes (gigantism in smaller, and dwarfism in larger). Factors involved:
- climate conditions (cooler climates favoring larger body size)
- island area (larger islands can support larger individuals)
- island isolation (immigrant selection favoring larger individuals)
- ecological interactions play a larger role

Question 30

gigantism and woodiness in plants

Answer 30

Woodiness, arboresence occurred repeatedly on islands – assocated with ecological shifts from herbaceous ancestors.
- woodiness suggests greater longevity
- associated with shift from r-selected strategies to k-selected strategies

Question 31

changing rate of colonization (recent invasions)

Answer 31

• decline of mammal diversity associated with arrival of humans
• antropogenic loss and transformation of native environments proceed in geographically nonrandom fashion, spreading from sites of human colonization toward remote sites.
• impact on the islands of remote Oceania: Polynesia colonization (warefare = loss of native species); Cook (brought disease)
• rate of extinction on islands extraordinarily high