1. Birds on Islands Why have islands always fascinated biologists?
Allow for tests of evolutionary and ecological theory
Simplified community assemblages
Lower diversity
Fewer predators
Emigration/immigration
Source/sink models
Isolation
Divergence/speciation
Species-area relationships
i.e. how does island size, distance between islands, correlate with diversity and/or species loss?
Important applications in conservation biology of habitat fragments

2. What is life like on islands?
Mild climate (mediated by stable temperature of oceans)
Lower predation and parasitism rates
All of this leads to:
Improved survival
Higher population densities
Greater competition for resources
What does this mean for reproductive strategy, as compared to continental populations?
Produce fewer, but higher quality offspring (K-selection)
Larger eggs
Greater parental care
Long-term pair bonds
Lower EPC’s, increased paternal care
Lower habitat availability, and possibly greater cooperation?

3. Covas et al. 2012
Do reproductive life history traits and associated behaviors of island birds differ predictably from their closest mainland relative?
Do islands follow the same life history trends as continents with respect to latitude (tropical vs. temperate)?
Compared 153 species pairs of island species and closely related continental species
Passerines make up 2/3 of sample and non-passerines 1/3.

4. Mating system and parental care on islands
Found significant increase in frequency of cooperative breeding
No change in incubating sex or rate of male incubation
(females more likely to incubate or spend more time incubating rather than more equal investment as predicted)

5. Clutch Size More influenced by latitude than insularity M = mainland
Clutch size increases greatly with latitude on the mainland, but not on islands
At high latitudes islands have a stronger effect on clutch size (more likely to be smaller than on mainland)
M = mainland
I = island

6. Egg Volume
For the majority of species pairs, eggs are bigger in island species than in
corresponding mainland species.

7. Developmental periods
Significantly longer on islands
- Incubation period longer for island birds

8. Nestling period:
For the majority of species pairs, nestling period is longer on islands than in
corresponding mainland species.
Less nest predation? More R selection?

9. Further evidence for K-selection strategy

10. Conclusions
Island colonizers usually have bi-parental care (uni-parental care less successful on islands) and often switch to cooperative breeding
Lower fecundity on islands
But exaggerated by latitudinal gradient, because clutch size increases rapidly with latitude on mainland
Larger eggs and longer time in nest suggests release from nest predation
Compare to tropical birds which want to reduce time in and around nest due to high nest predation
Island birds demonstrate K-selected reproductive strategy (long life span and saturated habitats = high competition of space and resources), invest in quality over quantity
Low clutch size
Large eggs
Long incubation period
Long time in nest
Long post-fledgling care phase
Milder climates on islands leads to increased adult survival, which has important consequences for competition and lifetime breeding strategies—Note: Many of these hypotheses are speculative and need more testing, but this study (Covas 2012) is a nice test of some of them.

11. Evolution on islands: Founder effects
Serial founder effects, or serial bottlenecking effect leads to
more and more reduction in allelic diversity as a subset of
each founding population founds a new population.

12. If a species makes it through initial bottlenecking, allelic
diversity will increase again in long run.

13. Increased body size with length of time of isolation: why?
PC 1 (bird size)
R2=.62
Isolation time (years)
Data from Manacus manakins in Bocas del Toro

14. Island Biogeography Theory
MacArthur and Wilson
Species diversity is a function of:
Island area
Smaller islands more subject to species loss and inbreeding
True for real islands and habitat fragments
Distance to next island
Isolated islands subject to species loss and rarely gain new species
True for real islands hand habitat fragments
Quality of dispersal corridor between islands
More applicable to habitat fragments
Edge effects (shape of island and amount of interior space as opposed to edge).
This has more to do with application to habitat fragments. Fragments with edges are vulnerable to infiltration by predators, for example. In the case of birds, habitat fragments with lots of edge are vulnerable to cowbird nest parasitism.