Avian Ecology (Animal Ecology 516)

Study Guide


Contents

Schedule | Guidelines | Ecological Survey | Foraging Theory | Habitat Selection | Migration | Territoriality | Social Behavior | Mating Systems | Population Biology | Life-history Traits | Community Ecology


Schedule

Date and Topic

13 Jan. Introduction to Avian Ecology

15 Jan. Survey of Avian Diversity

20 Jan. Foraging Theory/Habitat Selection

22 Jan. Mike Schiavone leads discussion on Habitat Selection

27 Jan. Migration

29 Jan. Erika Severaid leads discussion on Migration

3 Feb. Territoriality

5 Feb. Liessa Thomas leads discussion on Territoriality

10 Feb. Social Behavior

12 Feb. Jessamine Fung leads discussion on Social Behavior and Molecular Ecology

17 Feb. Mating Systems

19 Feb. Meg Holt leads discussion on Mating Systems

24 Feb. Population Biology

26 Feb. Brian Anderson leads discussion on Habitat Fragmentation and Conservation

3 Mar. Population Regulation

5 Mar. Mid-term Exam

10 Mar. Life-history Traits

12 Mar. Gian Dodici leads discussion on Life-history Traits

Spring Break

24 Mar. Community Ecology

26 Mar. David Horn leads discussion on Community Ecology

31 Mar. Field Methods

2 Apr. Discussion of Field Methods

7 Apr. Data Analysis

9 Apr. Optional Field Trip

14 Apr. Student Presentations

16 Apr. Student Presentations

21 Apr. Student Presentations

23 Apr. Molecular Ecology

28 Apr. Conservation Applications

30 Apr. Future Directions in Avian Ecology

7 May Final Exam (9:45 - 11:45 AM)


Study Guidelines

AEcl 516 students are responsible for understanding the points covered in this outline. They should review this outline and make sure they understand it, including points that were not mentioned in class. They should pay special attention to underlined items, which denote terms, expressions, and concepts that should be part of the vocabulary of every avian ecologist. If students are not absolutely sure they understand these points or underlined items, they should ask for explanation(s) in class or during the instructor's office hours.


Ecological Survey of Major Groups

I. Overview of ecological categories

Families are generally morphologically similar and thus similar in diet and foraging behavior.

Some groups (e.g., Order Passeriformes and Family Emberizidae) quite diverse.

A. AQUATIC

1. Seabirds

Capable of ranging across oceans.

Distinctly tropical and temperate subdivisions.

All adapted to water-air interface.

2. Coastal and interior waterbirds

More diverse than seabirds because they are adapted to more complex water-land interface.

Feed in water column or on bottom or shore.

B. TERRESTRIAL GROUPS DIVIDED PRIMARILY BY DIET

Carnivores and scavengers

Insectivores -- Gleaners can be branch, twig, and leaf gleaners

Frugivore -- Mainly tropical

Nectarivores

Others -- Such as Ratites (Superorder paleognathae)

II. Seabirds

A. GENERAL ECOLOGY

1. Feed on fish or plankton in oceans.

2. Some always forage within a few miles of shore; others capable of life on the open ocean.

3. All breed on land; most use small islands.

- E.g., "guano" islands off South America, where millions of seabirds breed and many tons of excrement are mined and exported each year.

4. Mostly in four Orders: Order Procellariiformes (Tube-nosed swimmers), Order Sphenisciformes (Penguins), Order Pelicaniformes (Totipalmate Swimmers), Order Charadriiformes (Shorebirds, gulls, auks, etc.).

5. Diversity of foraging behavior among families.

- dipping, aerial pursuit, aerial piracy, skimming, pattering, hydroplaning, surface filtering, surface seizing, scavenging, surface plunging, deep plunging, pursuit plunging, pursuit diving (wings), pursuit diving (feet), and bottom feeding.

6. "Aerial piracy" called kleptoparasitism.

7. Diversity among sympatric species.

- E.g., Galapagos Islands have 3 boobies and 1 tropicbird that all catch fish by plunging:

- The tropicbird is much smaller, feeds far from land, and specializes on flying fish.

- Blue-footed Booby near shore.

- Masked Booby offshore, between islands.

- Red-footed Booby away from islands.

8. Mostly widespread distributions, perhaps because land barriers that exist today (like South America) are fairly recent.

- Exceptions: 3 families restricted to cold temperate waters: Alcids (auks, puffins, murres) of northern hemisphere, Penguins (Spheniscidae) of southern cold seas, and Diving petrels (Pelecanoididae).

9. Convergence?

a. Storer (1960) pointed out the possible convergence between:

- the southern Hemisphere penguins (submarine flight only), diving petrels (submarine and aerial flight), and petrels (aerial flight only) and

- the northern hemisphere great auk, razor-bill, and gulls.

- convergence not perfect: small-bodied species in the north, fewer, larger-bodied species in the south.

B. PROCELLARIIFORMES

1. One of the (two) families most completely adapted to life on the sea.

2. Tube noses and well developed salt glands.

3. Feed on plankton, small fish, etc. from the surface.

4. Albatrosses--dynamic soaring capabilities.

5. Shearwaters--propel themselves with their feet while cutting the surface with their bills.

6. Storm petrels ("sea swallows") flutter across the surface and feed on plankton.

7. Reproductive rates low, usually 1 egg per year and 1 every other year in larger forms.

C. PELICANIFORMES

1. Totipalmate feet--all 4 toes connected by webbing to produce a large paddle.

2. Large body size, generally, and feed on large fish.

3. Boobies, gannets, and tropicbirds plunge dive.

4. Tropicbirds specialize on flying fish.

5. Pelicans--ocean forms plunge dive about 1 body length, using pouch as a net; coastal and interior forms filter-feed for fish and plankton while swimming on the surface.

6. Frigatebirds are avian pirates.

7. Cormorants--more temperate than other Pelicaniformes, more often associated with coastal environments.

- Catch fish while diving underwater, starting from a swimming position.

- Used commercially in Japan.

D. OTHER OFFSHORE BIRDS IN TROPICS ARE GULLS AND TERNS

1. Eat fish and plankton picked from the surface or obtained by plunge diving.

2. In winter, jaegers and phalaropes, which pick plankton from surface and may spin to concentrate prey.

III. Coastal and interior waterbirds

A. SWIMMING BIRDS

Feed on or in the water (or bottom) by swimming on it or diving in it.

1. Cormorants and anhingas (both Pelicaniformes) have feathers that get wet; wings must be spread to dry.

- Feed primarily on fish.

2. Duck-like birds.

- Loons and grebes are highly specialized for diving.

- Eat fish (smaller forms also eat aquatic invertebrates).

- Breed primarily in temperate lakes and ponds and winter on coasts.

3. Ducks and geese (Family Anatidae) belong to one of the most diverse families of birds.

B. AERIAL FORAGERS

Mostly of the Family Laridae are aerial foragers

C. LARGE WADERS

e.g., herons, egrets, and bitterns, storks, ibises, spoonbills, flamingos, cranes, limpkins.

D. SMALLER SHORE AND MARSH BIRDS

Many shorebirds and Gruiformes (rails, coots, moorhens, etc.).

E. CARNIVORES AND SCAVENGERS

Hawks, eagles, owls, shrikes, roadrunners, hornbills.

F. INSECTIVORES

1. aerial insectivores, such as swifts, swallows (passerines).

2. flycatching insectivores, such as flycatchers (New and Old World passerine families), barbets, bee-eaters (Old World), motmots (New World), rollers (Old World), puffbirds (New World), and todies (West Indies).

- The passerines tend to have smaller bills and be mor active foragers than the non-passerines.

3. nocturnal insectivores, such as potoos, frogmouths, nightjars, and owlet frogmouths.

4. bark insectivores such as creepers, woodcreepers, nuthatches, and woodpeckers.

5. ground insectivores.

6. gleaning insectivores.

G. FRUGIVORES

1. Can be divided into:

- granivores, which eat hard seeds and usually destroy them, and

- frugivores, which eat soft fruits and may disperse the seeds.

H. NECTARIVORES

Hummingbirds, honeycreepers, bananaquits, flower-piercers, honey-eaters, flowerpeckers, and sunbirds.

I. OTHERS

Ratites (cassowaries, rheas, emus, ostriches), Galliformes, haziness, honeyguides, corvids, kiwis.


Foraging Theory

Difficult to draw distinct lines between foraging behavior, migratory and other movements, and habitat selection.

Better to show how these relate, not to worry about lines.

Primary researchers: John Krebs (Oxford), Steve Lima (Indiana State)

I. Foraging ability is important

A. VITAL TO SURVIVAL AND REPRODUCTION--probably strong selection to forage efficiently and safely.

B. EXAMPLES OF IMPORTANCE OF FORAGING

1. a small sparrow wintering in Arizona needs to find a seed every 1-2 seconds for 10 hours/day.

2. a wintering titmouse needs an insect every 3 seconds

3. tropical insectivores must forage over 90% of the day to survive.

C. TIME BUDGETS (tremendous time spent foraging) show importance of foraging.

II. Determinants of foraging behavior

A. CONSTRAINTS

1. Anatomy and physiology.

2. These are themselves selected and so should enhance, rather than limit, ability to forage.

3. Being tied to an area limits availability of foraging areas

-nest site.

-territory.

-roost site.

B. WHERE SHOULD FORAGING BE DONE? Distribution of food is important.

1. May be important in settling after migration and habitat selection.

2. Even, predictable resource distribution favors foraging in a relatively small area and defending it (territoriality or dominance).

3. Irregular, patchy resources favor wider movements, lack of resource defense, possibly flocking.

C. HOW SHOULD FORAGING BE DONE?

1. Importance of efficiency suggests maximizing some indication of benefits while minimizing costs.

2. Benefits can be calories, nutrients, either of these per unit time--the currency.

3. Costs can be handling or processing time, risk of predation, energy and risk expended on interference competition.

4. Optimal foraging models have been developed.

- not optimum in the sense of the best that can be, but maximizing benefit/cost ratio subject to constraints.

5. Models predict outcomes, not mechanisms.

- essentially treating individuals as decision- or choice-makers.

- solution may be an optimal "strategy."

- need not require consciousness on the part of individual birds, but it does raise research. questions about mechanisms.

- outcomes can be tested in field and lab.

6. Group foraging.

- more eyes to find food, move to productive sites.

- young birds learn form older ones.

- where resource patches are not rapidly renewed, extreme depletion of a patch allows flock to assess patch quickly.

- information centers.

- mixed-species flocks in tropics.

7. Individual behavior.

- searchers tend to be generalists, consume prey types that don't require pursuit.

- e.g., insect gleaners.

-pursuers tend to be specialists (including sit-and-wait strategy).

-e.g., flycatchers.

8. Switching indicated if items avoided when rare, preferred when common.

-could be because of a search image.

III. Optimal foraging models

Experimental tests of small questions, hoping to fit these together into a big picture.

Optimal foraging models are popular, despite problems, because they help organize thoughts and lead to good questions.

A. GREAT TITS (John Krebs) offered a variety of food items on a treadmill

1. Tended to selected larger items, which were optimal in terms of energy consumed/unit time.

2. Wider spacing of food items on treadmill led to consumption of all sizes

B. REDSHANKS (Goss-Custard) feed on marine worms--field study

1. When variety of sizes present, large ones selected, small ignored.

2. When large ones rare, more small ones taken.

C. PIED WAGTAILS (Nick Davies) obtained greatest energy/time from medium-sized dung flies

D. MARGINAL VALUE THEOREM

1. Leave a patch when net intake of food falls below average of the habitat in general.

2. Giving up times (GUT) as originally formulated.

- Giving up Densities (GUD) in some models.

E. PITFALLS

1. Cannot capture all realities without becoming too complex.

2. Criteria for rejection often fuzzy.

3. Many models don't allow for birds' sampling of the environment -- sometimes invoked to explain data that don't quite fit.


Habitat Selection

Important to fitness, useful information for managers.

Habitat Selection different from Habitat Utilization.

Primary researchers: Martin Cody (UCLA), Fran James (Florida State)

I. Generalists and specialists

A. CHICKADEES are generalists, found in many forest types

B. KIRTLAND'S WARBLER

- a specialist; nests in stands of jack pine around 8 years old.

II. Birds have evolved cues to appropriate habitat--hard to identify

A. QUANTITATIVE APPROACH to identifying preferred habitat.

1. Fran James used multivariate statistics to identify habitat preference, critical requirements.

-15 measurements of vegetation within a 0.1-acre circle, usually centered on a singing perch.

B. COUNTS OF BIRDS BY HABITAT REFLECT PREFERENCES, often show differences .

III. Proximate vs. ultimate factors

IV. Proximate factors favoring use of an area

A. TRADITION

B. PREVIOUS REPRODUCTIVE SUCCESS

C. SOCIAL ATTRACTION

D. AVOIDING COMPETITION OR PREDATION

E. ASSESSING RESOURCE (FOOD OR HABITAT) PREFERENCE

V. Assessing resource (food or habitat) preferences

Habitat preferences inferred from comparison of use and availability.

A. COMPARISON results in list of habitats preferred and avoided.

B. PITFALLS

1. Measured use of foods may not reflect actual preference--some may be ingested incidentally.

2. Habitat studies may assess availability within a home range or territory, but this ignores habitat selection involved in initial placement of the home range.

C. JOHNSON (1980) POINTED OUT CONDITIONAL NATURE OF RESOURCE SELECTION, importance of scale

1. First-order selection is of geographical range.

2. Second-order selection is individual or group home range.

3. Third-order selection is usage of habitat components.

4. Fourth-order selections of particular food items at a foraging site.

D. Testing

1. Neu et al. (1974) give chi-square approach to testing use-availability.

2. Johnson (1980) recommended using ranks.

VI. Selected references for assessing resource preferences

Alldredge, J. R., and J. T. Ratti. 1986. Comparison of some statistical techniques for analysis of resource selection. J. Wildl. Manage. 50:157-165.

Alldredge, J. R., and J. T. Ratti. 1992. Further comparison of some statistical techniques for analysis of resource selection. J. Wildl. Manage. 56:1-9.

Byers, C. R., R. K. Steinhorst, and P. R. Krausman. 1984. Clarification of a technique for analysis of utilization-availability data. J. Wildl. Manage. 48:1050-1053.

Johnson, D. H. 1980. The comparison of usage and availability measurements for evaluating resource preference. Ecology 61:65-71.

Neu, C. W., C. R. Byers, and J. M. Peek. 1974. A technique for analysis of utilization-availability data. J. Wildl. Manage. 38:541-545.

Pietz, P. J., and J. R. Tester. 1983. Habitat selection by snowshoe hares in north central Minnesota. J. Wildl. Manage. 47:686-696.

Thomas, D. L., and E. J. Taylor. 1990. Study designs and tests for comparing resource use and availability. J. Wildl Manage. 54:322-330.


Migration

Arctic tern annually travels from Arctic to Antarctica.

Ruby-throated hummingbirds, which weigh 3-4 g, crosses the Gulf of Mexico but hawks and vultures don't.

Primary researchers: Ken Able (SUNY Albany), Sid Gauthreaux (Clemson), Frank Moore (Univ. Southern Mississippi), and Susan Skagen (USGS)

I. Definition

A. HOW SHOULD IT BE DEFINED?

1. Seasonal movement by a population.

- distinct from dispersal, a one-way movement.

- irruptive or invasive movements involve wandering.

2. Any movement.

- Faaborg (1988 text) uses this definition, which would include dispersal and wandering.

B. KINDS (under restrictive definition)

1. Breeding grounds to place of non-breeding (e.g., wintering grounds) and vice versa.

2. Molt migration of waterfowl.

3. Altitudinal migration.

II. Why of interest?

A. REQUIRES AMAZING ABILITIES to navigate, orient, and select suitable habitat in which to settle.

B. PROMINENT FEATURE OF AVIAN ECOLOGY, particularly of temperate areas.

C. OF ECOLOGICAL INTEREST ARE PROXIMATE AND ULTIMATE FACTORS leading to:

1. migration and

2. settling.

III. Terms

A. LONG-DISTANCE MIGRANTS have complete shift between breeding and wintering ranges.

Neotropical or Nearctic-Neotropical migrants in New World.

B. SHORT-DISTANCE MIGRANTS travel a shorter distance (e.g., altitudinal movement) and breeding and wintering ranges may overlap.

- Some defined as "Neotropical migrants" by PIF.

C. PARTIAL MIGRANTS -- some leave, others don't

D. WINTER RESIDENTS, SUMMER RESIDENTS reflect a temperate bias

E. DISTINGUISHED FROM PERMANENT RESIDENTS

F. LEAP-FROG MIGRATION

- Highest-latitude breeding populations winter at lowest latitudes.

- e.g., fox sparrows along western coast of U.S.

G. SITE FAITHFULNESS OR SITE FIDELITY can occur on breeding or wintering grounds

H. PHILOPATRY -- natal or breeding

1. Breeding philopatry usually shows sex bias (different for passerines and ducks).

2. Why are female ducks philopatric and males not?

I. NOMADIC

J. FLYWAY

K. STOPOVER areas used during migration

L. STAGING AREAS used prior to migration

IV. Habitat associations with migration pattern.

A. GRASSLAND SPECIES

1. Northern species more likely to migrate that southern-U.S. species.

2. Most winter in southern U.S. and Mexico.

3. presumably because of limited availability of grasslands farther south--llanos of Venezuela and pampas of Argentina.

-exceptions are upland sandpiper, Swainson's hawk, bobolink.

B. FOREST SPECIES

1. 80-100% leave northern coniferous forests, which have severe winters.

2. Most move to tropics or southern deciduous forests.

C. WATER BIRDS

- sandpipers and birds that summer on interior marshes and lakes leave.

V. Food habits affect migration pattern of a species.

A. TEMPERATE-BREEDING BIRDS AND INSECTS AND OTHER INVERTEBRATES

1. Majority of temperate birds feed on insects.

2. Terrestrial insects become inactive during cold weather.

- Many insects overwinter as pupae.

- Abundance of adults and pupae decline over the winter.

3. Insect eaters are the largest group if temperate migrants.

- Parids (chickadees and titmice), insect gleaners, add seeds to diet in winter, have heavier bills than similar-sized warblers, which have thin, sharp bills.

4. Aerial and aquatic insectivores are forced to migrate.

B. TEMPERATE-BREEDING BIRDS AND FRUIT

1. Most fruit gone by fall.

- thrushes and robins can winter in southern U.S., where moderate climate allows access to food.

C. TEMPERATE-BREEDING BIRDS AND SEEDS

1. Generally don't have to go very far south.

- crossbills and finches that feed on pine seeds don't have to deal with snow cover.

2. Tropics dominated by fruit-producers, so seeds not very available.

D. TEMPERATE-BREEDING BIRDS AND OTHER RESOURCES

1. Fish-eaters require open water.

2. Raptors face declining or inaccessible prey populations.

- Temperate owls benefit from longer winter nights, don't migrate as much as diurnal hawks.

3. Nectar-feeders leave, may move to areas with winter rains (e.g., some deserts, California).

4. Resources may be limited even if available.

- Productivity may decline during winter.

- Large concentrations of migrants in limited areas (like coasts).

E. TROPICAL SPECIES

1. Altitudinal migration presumable related to availability of fruit or other food.

F. PROMIXATE OR ULTIMATE CONTROL?

1. Many species initiate migration long before resources become limiting on the breeding grounds.

- may indicate that they are not driven away by resources in short supply (thus, innate, evolved mechanisms responsible), although declining levels of resources could be a cue.

2. There may be advantages to arriving on wintering grounds early.

VI. Settling on breeding or wintering grounds

A. GEOGRAPHIC DIFFERENCES

1. Few North American migrants go to the Amazon Basin

- Warbler densities highest in Central America and West Indies.

2. Many European and Asian migrants go to savannahs of tropical Africa or rainforests of southeast Asia.

3. Other forested habitat available--no need to go farther.

B. IDEAL FREE DISTRIBUTION -- spatial distribution of individuals after settling

1. Distribution responds exactly to distribution of resources.

- e.g., higher densities at rich resource patches.

2. Assumes all individuals get same amount of equivalent, and have perfect knowledge of the distribution.

3. Concept introduced by Fretwell and Lucas (1970)

C. DESPOTIC DISTRIBUTION of individuals

- Some individuals get more resources than others, by using aggression to restrict access of others to resources.

VII. Age and sex differences

A. MALES SOMETIMES WINTER FARTHER NORTH THAN FEMALES - WHY?

1. Males, needing to compete for territories on the breeding grounds first, are getting a head start.

2. Males have larger surface-to-volume ratios and can live farther north.

- Supported by observation of female raptors wintering farther north than males.

3. Dominant sex forces the subordinate sex to move farther south.

4. Difficult to distinguish these hypotheses, since males are often larger and dominant.

5. Paper by Ellen Ketterson and Val Nolan (Indiana University) in 1983 developed a model that takes all of these into account.

B. AGE DIFFERENCES may be related to same factors.

- Young males unlikely to compete successfully for territories, so winter with females, where survival is presumably higher.

VIII. Timing of migratory movements

A. MOLT USUALLY DOES NOT OVERLAP MIGRATION.

1. Energetic costs of both.

2. Waterfowl become flightless.

B. CLIMATE AND WEATHER

1. Snow and ice can affect movements.

2. Long movements timed to coincide with tail winds--associated with fronts.

C. PHOTOPERIOD may be proximate cue, causing Zugunruhe (pre-migratory restlessness).

IX. Migration pros and cons

A. MIGRATION FAVORED IN SOME SPECIES

1. Temperate zone could have

- more food.

- lower nest predation.

2. Interference competition could force birds to leave.

B. PERMANENT RESIDENTS IN TEMPERATE ZONE

1. suffer survival risks of overwintering.

2. gain access to nest cavities (50-70% of hole nesters are residents) and have good reproductive success.

C. PERMANENT RESIDENTS IN TROPICS

1. small clutches, low reproductive rate.

2. high survival.


Territoriality

I. Setting the stage: Competition

A. WHAT IS COMPETITION?

"when many individuals exploit the same limited resources, they are competitors" -- Krebs and Davies' textbook

1. Both (or all) competitors are affected negatively

- Concept from general ecology--intraspecific comp.

- Can result in winners and losers, but even winners are affected negatively

2. Many kinds of resources can be limited

- food, water, shelter, space, mates

B. WHEN IS COMPETITION EXPECTED?

- When resources are in short supply

- If resources are abundant, no negative effects

C. SIMPLEST KIND: SCRAMBLE OR EXPLOITATION COMPETITION

1. No behavioral interaction

- no fighting, displaying, defense

2. Efficiency favored

- first access, good searching ability, rapid consumption

3. Expected spatial distribution of individuals: ideal free distribution

D. INTERFERENCE COMPETITION--RESOURCE DEFENSE

1. Aggressive behavior or displays

a. Behaviors reduce access of competitors to area

b. Aggression is costly--energy, risk

c. Example: Great Tits in Wytham Wood, studied by John Krebs (Oxford)

- oak woodland fills first, then hedgerows, where food is less abundant, breeding success lower

- fewer ind. in oaks than expected under ideal free distribution

2. Despotic distribution of individuals

- some ind. get more resources than others

3. When is resource defense expected?

- When benefits of behavior exceed costs

- Idea developed by Jerram Brown (SUNY Albany) with respect to territoriality: economic defensibility

II. Territoriality

A. A TERRITORY IS A "DEFENDED AREA"

- Simplest definition, although defense is problematic

- Usually provides exclusive access to resources

B. ESPECIALLY COMMON AMONG BIRDS

- Because birds are visual creatures, facilitating displays, and resources not highly clumped?

C. EXAMPLES

- Type A (all-purpose) in birds

- Nesting territories in colonial species (Type C)

- Leks

D. EXPECTED TO OCCUR WHERE RESOURCES ARE OF INTERMEDIATE ABUNDANCE AND ARE DISTRIBUTED FAIRLY EVENLY

- No benefit to defending super-abundant resources

- Clumped resources too costly to defend from competitors

E. SIZE OF TERRITORY REFLECTS RESOURCE DENSITY

- Could do so by individuals adjusting size for foraging efficiency or for economics of defense.

- J. P. (Pete) Myers (now with W. Alton Jones Foundation) and colleagues studied Sanderlings in California, found that size reflected intruder pressure

F. SIZE OF TERRITORY REFLECTS ENERGY NEEDS

Example: Golden-winged Sunbird

III. HOW IS TERRITORIALITY RECOGNIZED BY OBSERVERS?

A. Territorial defense observed

- Advertisement, bird song, chasing

B. Individuals evenly spaced--uniform, regular, or overdispersed dispersion (spatial distribution at a given time)

a. One alternative: random--all individuals have equal probabilities of occurring at all locations, independent of locations of other individuals

- e.g., buzz bombs on London, slugs in garden

- Quantifiable with Poisson Distribution or nearest-neighbor analysis

b. Another alternative: clumped or aggregated--individuals are closer to each other, on average, than expected under a random distribution

- e.g., herding, flocking, attraction to rich patch of resources (as in ideal free distribution)


Social Behavior

Social behavior refers to interactions between or among individuals, which may or may not be in a group.

Social organization refers to the general patterns that structure social behavior in a species or population and may include spacing, foraging, and mating.

Social species are those that live in groups.

I. Kinds of groups

A. AGGREGATIONS, ROOSTING GROUPS

1. attraction to a resource

B. FLOCKS

1. inconsistent membership

- waterfowl

- Pete Myers asked, "Do Sander lings have friends?" and found that the answer was no.

- Dickcissels winter in flocks of hundreds of thousands

C. ORGANIZED GROUPS

1. Breeding colonies

2. Small groups

- individual recognition, more complex social interactions

3. Cooperative, or communal, breeding

- group includes non-breeding adults (helpers)

D. HAVE ALL KINDS BEEN FAVORED BY SIMILAR SELECTIVE PRESSURE?

- No. Breeding colonies, other social behavior seen by Wynne-Edwards as evidence for reproductive restraint

II. Selective advantages of group living

A. MORE EYES

- less time scanning means more time to forage

B. DILUTION OF PREDATION

- might work unless predators seek out groups

C. SELFISH HERD

W.D. Hamilton's "geometry for the selfish herd"

- examples may include colonial nesting, lekking

D. GROUP DEFENSE

- mobbing

E. INFORMATION CENTERS COULD FACILITATE FINDING FOOD

F. COOPERATIVE HUNTING, GROUP FORAGING

- Harris' hawk

G. GROUP SELECTION unlikely

1. Promoted by Wynne-Edwards (1962) as an additional level of selection, provoking controversy.

2. Selection has occurred among groups and weeded out individuals that do not behave in ways that promote the group's long-term survival and reproduction.

3. Many group displays (e.g., communal roosting) explained as means to assess population density so density could be regulated at a level that would not over-exploit the resource base.

4. Would explain altruistic behavior, floaters, reproductive inhibition.

5. Often recognizable by the statement, "...for the good of the species."

6. Criticized by George Williams (1966), John Maynard Smith, Richard Dawkins, and others, who carried the day among behavioral ecologists.

-Individual selection would be expected to be stronger, resulting in the spread of behaviors that benefitted individuals but not the group, i.e., cheaters.

III. Costs of group living

A. INCREASED CONSPICUOUSNESS

B. COMPETITION FOR FOOD, OTHER RESOURCES

- disturbance of prey: Individual Redshanks foraging in mudflats cause their prey to burrow in

C. INCREASED RISK OF CARING FOR UNRELATED OFFSPRING

- For males, risk of being "cuckolded"

- For males and females, risk of intraspecific (or conspecific) brood (or nest) parasitism--cliff swallows

D. ECTOPARASITES

- cliff swallows

E. TOTAL COSTS HARD TO QUANTIFY, but presumably do not outweigh the advantages of group living

IV. Parental behavior--definitions

A. PARENTAL CARE

- any form of parental behavior that appears likely to increase the fitness of a parent's offspring

- some ambiguous behaviors--territorial defense, courtship feeding

B. PARENTAL EXPENDITURE

- expenditure of parental resources (including time and energy) on parental care -- i.e., energy cost

C. PARENTAL INVESTMENT

- extent to which parental care reduces parent's future reproduction--usually refers to each individual offspring--fitness cost

D. PARENTAL EFFORT

- parental investment on all progeny

- component of reproductive effort, along with mating effort

V. Types of parental care

A. BIPARENTAL CARE

- common in altricial birds

B. UNIPARENTAL FEMALE CARE

- dabbling ducks

C. UNIPARENTAL MALE CARE

- polyandrous birds, such as some shorebirds

D. FACTORS INFLUENCING TYPE

1. Unequal parental investment in endotherms is associated with female care as the prevalent pattern

- Robert Trivers suggested that anisogamy (unequal size of gametes in the sexes) led to greater costs to females, committing them to continue investing to avoid wasting their investment

- Criticized as the Concorde fallacy

2. Internal fertilization in birds

- Means that males can have higher certainty of paternity than if fertilization were external. This may favor biparental care.

3. Payoff for desertion--a game-theory model developed by John Maynard Smith

a. Best decision depends on what partner does

b. Find pair of strategies that is an ESS

c. Pair's reproductive success depends on

-amount of parental care

-number of eggs laid

d. For females, trade-off between eggs and care

e. Assign survival probabilities with 0, 1, and 2 parents, respectively

f. Deserting male mates again with assigned probability

g. Deserting females lay an assigned number of eggs, females that care for their offspring lay an assigned, smaller number

VII. Parent-offspring conflict

A. PARENTAL INVESTMENT (PI) DETERMINED BY TRADE-OFF between increasing fitness of current offspring and decreasing future reproduction

B. THE PI DEMANDS OF AN OFFSPRING ARE INFLUENCED BY SAME TRADE-OFF, but relatedness to future offspring (0.5 or 0.25) is less than to itself (1.0)

C. OFFSPRING MAY DEMAND MORE FOOD THAN PARENT IS WILLING TO SUPPLY

D. PARENT AND OFFSPRING MAY DISAGREE OVER TIME OF TERMINATION OF PARENTAL CARE

- may explain parental aggression at this time, e.g., aggression toward fledglings

E. OFFSPRING MAY FAVOR SIBLICIDE MORE THAN PARENT(S)

- Observations usually indicate few parental attempts to control aggression between nestlings


Mating Systems

I. Mating Systems Are Shaped By Sexual Selection

A. SEXUAL SELECTION

1. A distinct kind of natural selection.

2. Selection for traits and behavior(s), related to mating, that have increased the number or quality of offspring produced by individuals with the traits or behavior(s).

3. Intra-sexual selection is competition for access to mates (or fertilizable gametes).

- Usually by males

- Aggressive behavior (e.g., territoriality, dominance mate guarding) favored

- Morphological adaptations (larger size, sperm competition)

- Singing, displays directed at members of own sex

4. Inter-sexual selection, or mate choice.

- Usually by females

- "Coy" behavior favored, because evaluation of mate quality takes time

- Can be based on resources controlled by male

- Can be based on likely parental contribution of male

(e.g., courtship feeding some birds)

- Can be based on size or age of male

- Can be based on male ornamentation (e.g., Peacocks, birds-of-paradise) or mating structures (bowerbirds). Brighter coloration may indicate greater disease resistance, according to W.D. Hamilton (Oxford) and Marlene Zuk (Univ. California, Riverside)

- In lekking species (no parental care, no resources held by males) females are free to choose on basis of good genes or something indicating good genes

5. Inter- and intra-sexual selection often work together (e.g., leks, inciting behavior of female ducks)

II. Why are males usually brightly colored and competitive, and females usually choosy?

A. ANISOGAMY--sperm smaller than egg

1. Unequal size of gametes means that, for the same amount of energy, males can produce more gametes, and thus more potential offspring, than can females.

B. FEMALES GENERALLY HAVE HIGHER PARENTAL INVESTMENT

C. MALE REPRODUCTION LIMITED BY NUMBER OF EGGS THAT CAN BE FERTILIZED

1. Fertilizable eggs usually related to access to females, i.e., females in short supply relative to demand--hence male competition.

D. FEMALE REPRODUCTION LIMITED BY NUMBER OF OFFSPRING THAT CAN BE PRODUCED, HENCE BY RESOURCES

1. Laying, parental care increase the females' investment relative to males.

E. EXCEPTIONS THAT PROVE THE RULE:

- If males care for the eggs and young, females would be expected to be competitive, more brightly colored than males

- Jacanas, phalaropes, and painted snipes support this prediction

III. Avian mating systems

Traditional classification based on number of mates.

A. MONOGAMY--ONE MATE

1. Pair bonds lasting for much of nesting season are characteristic of over 90% of avian species.

2. Both sexes must benefit for monogamy to be selectively advantageous.

3. Both sexes presumably needed for high reproductive success.

4. Often assumed to be the ancestral condition for evolution of other systems.

B. POLYGAMY--ONE SEX HAS MULTIPLE MATES

1. Polygyny--one male, multiple females.

2. Polyandry--one female, multiple males.

- Occurs in 2-3 dozen species

- Serial or simultaneous

C. POLYGYNANDRY--MULTIPLE MALES, MULTIPLE FEMALES

1. E.g., Acorn woodpeckers, which live in groups.

2. Promiscuity also refers to this system, generally connnoting a lack of lasting bonds between the sexes (e.g., leks).

E. IN ABOUT 3% OF AVIAN SPECIES, CLUTHES ARE ATTNEDED BY MORE THAN TWO ADULTS

1. Groups may include non-breeders.

2. Breeders may be monogamous, polygamous, or polygynandrous.

F. BONDED INDIVIDUALS MAY MATE OUTSIDE OF BONDS

1. Extra-pair copulations (EPCs).

- Can lead to extra-pair fertilizations (EPFs)

- Originally postulated by Robert Trivers (Univ. California, Santa Cruz) as a male tactic.

IV. Evolution of polygyny

A. POLYGYNY THRESHOLD MODEL

1. Classical explanation, developed in 1960's by Gordon Orians (Univ. Wahington), Jared Verner (USFS, California), and Mary Willson (USFS, Alaska).

2. Females must be able to raise young without males' assistance. This was later (1977) called the Environmental Potential for Polygamy (EPP) by Steve Emlen (Cornell Univ.) and Lew Oring (Univ. Nevada, Reno). Orians et al. worked primarily with Red-winged Blackbirds, which inhabit highly productive marshes.

3. In heterogeneous environment, male territories vary in richness of resources.

4. Females settle on rich territories first, form monogamous bonds.

5. As more females arrive, there comes a time when newly arriving females can have higher fitness by becoming the second female on a rich territory than by being the sole female on a poor territory. This is the polygyny threshold.

6. This is a form of resource defense polygyny (Emlen and Oring 1977).

B. PREDICTION OF POLYGYNY THRESHOLD MODEL

1. Many polygynous species occur in productive, heterogeneous habitats (marshes, grasslands), which would be expected if polygyny in these species evolved acording to this model.

C. MALE DOMINANCE POLYGYNY

1. Leks occurs in some species with precocial young. Males usually defend a small territory (Type D) used only for displaying and mating.

2. In any tropical frugivores, females can raise altricial young alone (manakins and cotingas in New World, birds of paradise and bowerbirds in Old World).

3. Most nectarivores, such as hummingbirds and sunbirds, are polygynous.

4. Highly polygynous species can have highly ornamented males, delayed maturation of plumage, and secondary tactics for mating.

D. HAREM DEFENSE POLYGYNY

1. Rare in birds.

V. Evolution of polyandry

A. MOST POLYANDROUS SPECIES ARE SANDPIPERS

1. Frank Pitelka (Univ. California, Berkeley), Lew Oring, and Don Jenni (Univ. Montana) have tried to understand its evolution.

B. HIGH ARCTIC ENVIRONMENT

- Short breeding season

- Distant from wintering grounds

- Abundant, accessible insects for precocial sandpiper young

- Most sandpipers monogamous

- Sandpipers lay 3 or, usually, 4 large eggs

C. PREADAPTATIONS:

1. Females have depleted energy reserves after laying, need to replenish them by feeding.

2. Males, who take over incubation, develop strong attachment to nests.

D. IF EPP IS HIGH,

1. Double-clutching can evolve, with both parents caring for a clutch.

2. Female can lay a clutch for another male, resulting in serial polyandry.

3. Simultaneous polyandry occurs when females defend a territory and males subdivide the territory.

E. POLYANDROUS SYSTEM MAY VARY WITH LATITUDE

-Spotted sandpipers, jacanas exhibit serial polandry farther north and simultaneous farther south

VI. Breeding in groups

A. COOPERATIVE (OR COMMUNAL) BREEDING

1. Monogamous pairs with helpers.

- Florida scrub jay (Glen Woolfenden, Univ. Southern Florida).

- Green woodhoopoes (David and Sandra Ligon, Univ. New Mexico).

- Several tropical wrens

2. Acorn woodpeckers range from monogamous pairs to groups exhibiting polygynandry. Studied by Walter Koenig (Univ. California, Berkeley) and Peter Stacey (Univ. New Mexico).

3. Groups consisting mostly of monogamous pairs are typical of groove-billed anis (Sandra Vehrencamp, Univ. California, San Diego) and Mexican jays (Jerram Brown, SUNY Albany).

4. Cooperative polyandry in Galapagos hawk.

B. RHEAS AND TINAMOUS HAVE A SYSTEM THAT IS SEQUENTIAL POLYANDRY FOR FEMALES, HAREM DEFENSE POLYGYNY FOR MALES

1. Groups form with one male, multiple females.

2. Females lay in common nest, than move on to another male, leaving the original male to incubate the eggs and raise the young.

C. OSTRICHES

1. Males pair with a major female. Other females in the group lay also, but most of these eggs are rolled away by the major female.

D. TASMANIAN NATIVE HENS

1. Polyandrous group, with related males.


Population Biology

I. What is Population Ecology?

A. STUDY OF FACTORS THAT CONTRIBUTE TO CHANGES IN POPULATION SIZE, namely:

1. Birth

2. Death

3. Immigration: only affects population growth if arriving individuls breed and leave offspring

4. Emigration

B. Dispersal includes immigration and emigration

II. Terms

Population -- Organisms living in a defined area -- often used in wildlife ecology to indicate population density

Population density -- number of individuals per unit area

N -- Population size

r -- Intrinsic rate of increase (Malthusian parameter)

K -- Carrying Capacity

Source Habitat -- Habitat in which reproduction exceeds mortality

Sink Habitat -- Habitat where population density can only be maintained by immigration

e -- Base of natural logarithms

-- (lambda), Finite rate of increase

Productivity

Survival

Survivorship

Discrete generations

Overlapping generations

Geometric growth

Exponential growth

Logistic growth

Limit cycles

Key factor analysis

Limiting factors

Population regulation

Density independent

Density dependent

Optimum sustained yield

Deterministic model

Stochastic model

Population viability analysis

Semelparity

Iteroparity

Age-structured population

Life table

Cohort

Stable age distribution

Stationary age distribution

Generation time

Net reproductive rate

III. Population Regulation

A. DENSITY-INDEPENDENCE

1. Density-independent factors operate independently of the density of the species (i.e., a density-independent mortality factor would result in a similar percentage of the population dying, regardless of population density)

2. Climatic factors are examples

- Cold weather

- Rain

- E.g., cold, rainy weather in the spring is associated with high mortality of juvenile grouse

3. Density-independent factors cannot regulate population density

B. DENSITY DEPENDENCE

1. Density-dependent factors result in population effects that vary with population density

- Regulating factors have little effect at low density, greater effect (lower reproduction and/or survival) at high densities.

- Anti-regulating factors result in higher reproduction or survival at higher densities (not many examples in birds; perhaps Allee effect and Fraser Darling effect)

2. Most prominent factors:

- shortage of resources

- predation, parasitism, disease

- increasing intraspecific social interaction

IV. Calculating population growth rates

A. GEOMETRIC

1. Discrete time, non-overlapping generations

B. EXPONENTIAL

1. Continuous time, overlapping generations

C. LOGISTIC

D. AGE-STRUCTURED POPULATION GROWTH

1. Reproduction and mortality vary with age

2. Life tables provide standard way to summarize data

3. Usually females only

4. Follow a cohort

- Ages (x) specified (usually years, starting with 0)

- Fertility schedule [b(x) or m(x)]

- Survivorship schedule [S(x)]

- Calculations for:

-- Proportion of cohort that survives to age x

-- Probability that an individual of age x survives to age x+1

-- Mean number of offspring produced in a lifetime [l(x)b(x)]= Net Reproductive Rate

-- Generation time (sometimes designated T), or average age of the parents of a cohort

Population projection

Leslie matrix good for age-structured populations

Incorporates age structure by using age classes (starting with 1)

Vector n indicates numbers of individuals in each age class at a given time, t

n1, n2, n3, etc.

Matix A contains information on survival and reproduction of each age class

Simplest case: birth-pulse model, in which all mothers give birth on the day they leave an age class and a post-breeding census just after the time of birth

More generally, a population projection matrix is used, which may or may not be a Leslie matix.

Stage-based populations can be analyzed with population projection matrices.

IV. Estimating population persistence time

A. ENVIRONMENTAL STOCHASTICITY (e.g., weather)

B. DEMOGRAPHIC STOCHASTICITY (e.g., sex ratio)

C. ANALYTICAL MODELS

1. Dan Goodman found that most important factors were:

r and the variance of r

D. SIMULATION MODELS

1. Spotted owls, Acorn woodpeckers

V. Population viability analysis

A. DEFINITIONS & HISTORY:

"A viable population is a population capable of maintaining itself without significant manipulation"

- over an agreed-upon time frame and

- with an agreed-upon level of certainty

Impetus: The National Forest Management Act (1976) required that all forests maintain viable populations of all vertebrate species on their lands.

Small populations are fragile because of chance events, or stochasticity.

PVA is the study of the ways in which habitat loss,environmental uncertainty, demographic stochasticity, and genetic stochasticity interact to determine extinction probabilities for an individual species.

All factors are important, and interactions among factors are especially important in small populations.

Note: all populations go extinct; the question is whether they are going extinct due to natural or human-caused factors

B. SPECIES/AREA RELATIONSHIPS - THE ROOTS OF PVA

1. Rate of decline in S (# Species) depends on:

- area

- degree of isolation

- time since isolation


Life-history Traits

I. General Concepts

A. LIFE-HISTORY TRAITS ARE BASIC FEATURES THAT AFFECT FITNESS, such as those dealing with growth, reproduction, and adaptations for survival.

B. TRADEOFFS PROBABLY EXIST such that evolving to put more time or energy into one thing (e.g., reproduction) may result in less time or energy for other things (e.g., adaptations promoting survival).

C. LIFE-HISTORY STRATEGIES, OR TACTICS, ARE PATTERNS INVOLVING SUITES OF TRAITS.

1. Tropical species, living in a relatively stable enviroment, often have long lives and low reproductive rates. Seabirds also exhibit this pattern.

2. Temperate species, living in a relatively unstable enviroment, often have short lives and high reproductive rates.

3. r- and K-selection postulated.

D. HOW HAVE THESE TACTICS EVOLVED?

1. Long-lived species should keep costs associated with reproduction low, living to "fight another day."

2. Short-lived species have little to lose by incurring high costs to reproduce.

II. Eggs and Broods

A. EGGS

1. Egg size

- Varies among species, representing a smaller proportion of female's body mass in species with larger body mass.

- Precocial species usually have larger (10-15% of female's body mass) eggs than altricial species (5% of female's mass).

2. Clutch size

A. Intensively studied

- discrete entity

- an estimate of annual reproduction in species that nest only once a year.

- varies within and among species (seabirds typically lay one egg; grouse often lay well over a dozen)

- can be experimentally manipulated

B. Optimal size results in most descendents

- Great tit study by Christopher Perrins indicated that nestlings weighed less in larger clutches and that lighter nestlings had lower survival rates.

- Optimal clutch size (most recaptures) was 9-10 eggs, similar to the modal clutch size (8-9 eggs).

C. Optimal clutch size affected by food availability and nest predation

- Precocial species have larger clutches than altricial species, presumably because the parents of precocial young do not have to feed them.

- Larger clutches take longer to lay, resulting in longer exposure of the nest to predation

- Hole-nesting species, which face less nest predation, have larger clutches than open-nesting birds.

III. Number of broods per nesting season

1. AFFECTED BY THE SAME GENERAL FACTORS THAT AFFECT CLUTCH SIZE

2. MAY BE INVOLVED IN A TRADEOFF WITH CLUTCH SIZE

IV. Maturity at hatching

A. PRECOCIAL YOUNG HATCH WITH THEIR EYES OPEN, are covered with down, and can leave the nest within a day or two

They are nidifugous, or nest fugitives.

B. ALTRICIAL YOUNG HATCH WITH EYES CLOSED, have little feathering, and require great amounts of care and feeding.

They are nidicolous, or nest dwellers.

C. SEMI-PRECOCIAL AND SEMI-ALTRICIAL BIRDS ALSO EXISt, but do not share all of the features listed above.

V. Growth, rate of development of individuals

A. AGE OF FIRST REPRODUCTION

1. Some finches in desert environments have been known to breed at just a few months of age.

2. In most birds, first reproduction occurs at about one year of age.

3. In many large birds of prey and seabirds, first reproduction may not occur until nearly 10 years of age.

B. GROWTH WIDELY STUDIED

VI. Survivorship

A. INVOLVED IN TACTICS, BUT HARD TO STUDY


Community Ecology

I. Community structure

A. DIVERSITY

1. Alpha diversity refers to a single habitat or location.

2. Beta diversity refers to the change in diversity between sites.

3. Gamma diversity refers to an area that has multiple habitats.

4. Common indices indicate something about total number of species and their relative abundances. Highest index values are for communities with many species and high evenness.

5. Species richness refers to the number of species.

B. NICHE

1. Rich history of attempts at definition, involving either the ecological role in the community or the range of conditions under which the species can live.

2. Hutchinsonian niche: n-dimensional hypervolume.

a. Concept suggested by G. E. Hutchinson (Yale).

b. Fundamental niche describes conditions that a species could live under in the absence of predators and competitors.

c. Realized niche describes conditions that a species is observed to live under (i.e., in the presence of predators and competitors).

II. Processes leading to community structure

A. COMPETITION

1. Widely seen as the primary force structuring communities (e.g., Cody, Faaborg, MacArthur, Schoener [UC Davis]). See III.

a. Competitive exclusion principle: species with identical ecological traits (niches) cannot coexist for long. Sometimes called "Gause's principle" because of his work testing this idea, published in 1934.

b. Much theoretical work indicating that species must be different to coexist.

- Ratios between adjacent species in a guild often approach 1.3 in length or 2.0 in mass.

- A ratio of this magnitude is sometimes termed a Hutchinsonian ratio because Hutchinson made it famous.

- One example is the Tufted Titmouse (ca. 22 g) and one of two species of chickadee (both ca. 11 g) that coexist in eastern North America.

- Another example is the five species of kingfishers that coexist in tropical America.

c. Character displacement: evolutionary change in a character in part of a species range, in response to competition with another species there.

B. HISTORY

1. Glacial advances, retreats

2. Evolutionary history, speciation

C. PREDATION

D. STOCHASTICITY

III. Evidence for importance of competition in avian communities

A. COMPETITION IMPORTANT IN OTHER KINDS OF COMMUNITIES.

B. PATTERNS CONSISTENT WITH MINIMAL ECOLOGICAL OVERLAP

1. Closely related species may often replace each other along ecological gradients, such as altitudinal gradients.

2. Overlapping species tend to have differing habitat preferences.

3. Species in the same habitats tend to (1) use different foods, (2) have different foraging techniques, or (3) subdivide the habitat in some other way.

4. Robert MacArthur, in a classic study, found that warblers in New England spruce forests tended to forage in different parts of the trees.

C. ECOLOGICAL SHIFTS WHERE COMPETITORS ARE ABSENT

1. Jared Diamond (UCLA) found, among birds of the Southwest Pacific Islands, shifts in altitudinal use, habitat use, and vertical zones used within a habitat.

D. EXPERIMENTAL EVIDENCE

1. Hard to come by.

E. EXCEPTION THAT PROVES THE RULE?

1. John Wiens (Colorado State) studies grassland and shrub-steppe bird communities and found widely overlapping niches.

2. Wiens invoked weather and the unpredictability of these dry systems, and the resultant infrequent nature of ecological "crunches," to explain the apparent lack of competitive exclusion.

IV. Communities on Islands

A. USEFUL FOR UNDERSTANDING COMMUNITIES

1. Communities often smaller, easier to study

2. Islands often very in size but have similar habitats

3. Differing avian communities on islands can provide insights into influences on community structure.

4. One can observe the assembly of a community after a natural disaster.

5. One can observe "relaxation" of avifauna on land-bridge islands.

a. 20% of forest avifauna lost in 70 years on Barro Colorado Island in Gatun Lake, Panama.

B. SPECIES-AREA RELATIONSHIP

1. More species on larger islands

2. Relationship described by power function.

a. S = c * A raised to the z power,

where S is number of species, A is area, c and z are fitted constants.

b. z ranges from 0.2-0.35.

c. linear plot on semi-log paper.

C. EQUILIBRIUM MODEL

1. Proposed by Robert MacArthur and E.O. Wilson (Harvard) in 1963

2. S is an equilibrium between immigration (colonization) rate and extinction rate, since

immigration rate falls, extinction rate increases, as S rises.

3. Immigration line lower for more isolated islands, resulting in lower S.

4. Extinction rate lower for larger islands, resulting in higher S.

D. PATTERN IN WEST INDIES

1. Studied by John Faaborg (Univ. Missouri).

2. Guild analyses revealed linear increases in number of species with either increasing island size or increasing S (relationship better with S because isolation effect contributes to scatter in size plots).

3. Within habitats (dry forest, wet forest), number of species per guild leveled off at an S of about 20. Thus higher S on larger islands is due to greater differences in species composition between habitats and greater number of habitats on large islands.

E. PATTERN IN SOUTHWEST PACIFIC ISLANDS

1. Studied by Jared Diamond.

2. Steeper species-area relationship (i.e., z over twice as large) than in West Indies

3. Size shifts within species are rare.

4. Assembly rules proposed to explain guild structure.

a. Among fruit pigeons, size was the key to coexistence. Similar-sized species coexisted only on the largest islands.

b. Among other guilds, habitat specialization was important.

5. Critics (e.g., Connor and Simberloff, in a 1984 book edited by Strong et al.) said patterns could be due to chance.

V. Large-scale Patterns

A. LATITUDINAL GRADIENT IN SPECIES RICHNESS--What causes it?

1. Ultimate factors that have been invoked:

- Time without drastic ecological disturbance, such as glaciers.

- Higher stability or predictability in tropics.

- Higher productivity of vegetation higher in tropics.

- Higher complexity of vegetation higher in tropics.

2. Proximate factors that have been invoked:

- Closer species packing.

- Availability of wider range of resources, such as fruits, flowers, and large insects.

B. CONTINENTAL COMPARISONS

1. Similar number of avian species in grasslands of North and South America and in shrubby vegetation of Mediterranean climates in California and Chile (Cody).

C. CONVERGENCE


URL: http://www.iastate.edu/~rkoford/avecol.htm

Updated 23 March 1998