Study Questions Exam II

(answers given below)

1.  Honey bees are considered to be advanced (or highly evolved) social insects.  In comparison, wasps and primitively social bees are considered to be "lower" on the evolutionary scale and their behavior is thought to be closer to the ancestral condition.

            Honey bees possess a signal called the vibration signal, which consists of one worker, often a successful forager, rapidly shaking its entire body up and down in a stereotyped and repetitive manner, usually while grasping another bee.  The signal does not release any specific response in recipients.  Rather, vibrated recipients exhibit a non-specific increase in activity, which leads to increased time spent performing the tasks appropriate for their age.  For example, vibrated older bees spend more time foraging, while vibrated younger bees spend more time engaged in brood care and food processing.  Under normal circumstances the vibration signal does not contain elements of aggression in honeybees, and the stinger is never protruded during its performance.

            Several primitive species of social insects also possess vibration-like displays.  In the wasp, Polistes exclamans, dominant females perform a display which consists of rapidly beating the abdomen up and down.  This display is aggressive (although the stinger is not protruded) and is used by dominant females to force subordinate workers to care for brood or leave the nest and forage.  In the carpenter bee (a primitively social bee), the dominant female is the most aggressive female in a nest.  If she finds an idle worker she will grab the bee and rapidly beat her abdomen up and down.  The beating of the abdomen appears to be a preparatory movement for stinging, and often the stinger is protruded in preparation for a sting.  Attacked  workers leave the nest and go forage.

     Based on these descriptions you are justified in thinking that:

a.  The comparative method can be used to hypothesize that the vibration dance of the honey bee is ritualized from an aggressive behavior, which evolved from an intention movement to sting.

b.  the evolution of the vibration dance involved the process of ritualization.

c.  the evolution of the vibration dance involved the process of emancipation (hint:  don't confuse response of the recipient with the motivation of the sender).

d.  the data provided suggest that the vibration signal of honey bees has an external referent, but that the meaning of the signal is uninfluenced by context.

2.  Most primates are highly vocal animals and occupy a wide range of habitats.  When comparing forest and savannah (grassland) species, you would predict that:

a.  forest species would possess calls of higher frequency than savannah species.

b.  the calls of grassland species would have a broader frequency range than forest species.

c.  the calls of all species would consist of rapidly repeated notes.

d.  the calls of the forest, but not the savannah, species would be degraded by unpredictable wind gusts and temperature fluctuations.

3. 

Hummingbirds are nectivorous.  In some tropical hummingbird species, males defend territories during both the breeding and non-breeding seasons.  The energy gained per day, number of flowers per territory, and the amount of time spent feeding on nectar and fighting by individual males for both seasons are given below:

                             E gain (Kcal)             Flowers/Terr.   Time Feed        Time defending

        Breeding              6-12                    450-4000            4.2 hrs                6.8 hrs                       

Non-breeding             17-30                   5000-6500           7.7 hrs                 2.7 hrs

You want to examine if territorial defense is based on Energy maximization or Cost minimization.  Based on estimates of the energy per flower and the energy expended in foraging and fighting, the following predictions were determined for how much energy should be gained per day, how many flowers should be defended, and how much time should be spent foraging on nectar and defending in order to maximize energy or minimize costs for individual males:

                         E gain (Kcal)    Flowers/Terr.   Time Feeding    Time Defending

 E max.             16-32                4500-7000           7.1 hrs               3.0 hrs

Cost min               0                   1500-2100           3.1 hrs                1.2 hrs

Note:  During the breeding season, males help their mates feed the young.  However, young birds are fed insects, not nectar, and all insects fed to the young must be caught in the male's territory.  Both parents must spend considerable time each day gathering insects. 

Based on this information you can conclude:

a.  Male hummingbirds are cost minimizers during both seasons.

b.  The male hummingbirds are energy maximizers during the non-breeding season, perhaps to build up body reserves for future breeding.

c.  A better currency for a foraging model during the breeding season would be "maximize rate of delivery to the nest".

d.  Foraging behavior is not well predicted in either season, because the currency that should have been used is "maximize energetic efficiency".

ANSWERS

1.  a.  True:  the vibration dance does appear to be a ritualized aggressive display.  In the most primitive species, the carpenter bee, the vibration-like behavior is a preparatory movement for stinging, and is an aggressive act that dominant bees use to force subordinates to forage.  In the next species, Polistes, the vibration -like behavior is still used by dominants to cause subordinates to work, but it no longer involves the protrusion of the stinger.  Finally, in honey bees, the vibration dance is non aggressive, is not associated with dominance, and the stinger is not involved.  The display now causes a non-specific increase in activity which enhances many different behaviors.  Thus, the form of the behavior changed during its evolution, from an aggressive, intention movement to sting to a non-aggressive signal to promote activity.  The behavior has therefore become ritualized.

       b.  True, as described above, the form of the display changed during its evolution.

       c.  True, because the motivation for the display also changed during its evolution.  It started as an aggressive act (carpenter bees), but evolved into a non-aggressive signal (honeybees).

       d.  False:  no evidence is provided to indicate that an external referent is involved; the signal does not refer to anything specific in the external world.  Furthermore, context does influence how recipients interpret the signal.  The signal causes increased activity which is expressed in a wide variety of specific tasks, depending upon recipient age.  Thus, the contextual cue of age influence the specific meaning of the signal for recipients.

2.  a.  False:  forest environments favor low frequency sounds, because these are less degraded as they pass through vegetation.  High frequency sounds are the most degraded in forest environments.

    b.  True:  vocal calls in grassland habitats, especially those designed to be broadcast over long distances, use a broad range of frequencies.  In grassland areas, the major source of degradation for sound is unstable air caused by wind gusts and thermal currents.  Animals have brief, unpredictable "window" of time in which the air is stable enough to transmit sound with minimum degradation.  This selects for trying to "fit as much information as possible" into these time periods, and thus song and calls in grassland areas use many frequencies and are complex (lots of trills and repeated notes).

    c.  False:  would be true for only grassland species (see b.)

    d.  False:  the opposite is true.  Main source of degradation in grasslands is unstable air due to wind gusts and thermal currents.  Major source of degradation in forests is echoes caused by vegetation.

3.  a.  False:  A C_min model does not predict a male's behavior during either season.  Cmin predicts no net gain of energy each day, territories that contain only 1500-2000 flowers, and low levels of foraging and defending.  In contrast, males gain 6-30 Kcal per day in both the breeding and nonbreeding season and spend more time foraging and defending than the Cmin model predicts.

    b.  True (maybe):  the energy gained/day, number of flowers defended, and time spent foraging and defending during the nonbreeding season are consistent with that predicted by the Emax model.  This may allow the males to "bulk up" for the next breeding season.  However, while the observed data fit the Emax model, this does not necessarily tell you the ultimate reason for why males are energy maximizers during the nonbreeding season (bulking up is just one possibility).

    c.  True:  neither the Emax or Cmin models predict how males are observed to behave in the breeding season.  This is likely to arise because during the breeding season males are not foraging only for themselves, but are also gathering insects to feed their young.  Under these conditions, males would be selected to maximize rate of delivery to the nest, and they would adjust the number of insects they catch/trip and their sensitivity to handling time and search time with distance traveled from the nest.

    d.  False:  maximize energetic efficiency applies to nectar feeding animals, like honey bees, who have to carry a load of food that is heavy relative to their body size.  Under these conditions, animals are predicted to reduce the load they carry with increasing distance traveled, to reduce wear on the body and extend the life of the insect, thereby maximizing the total amount of food collected for the colony over its lifetime.  Male hummingbirds do collect nectar when feeding for themselves, but they don't have to carry it back to a nest (they feed and digest the nectar where ever they are), and thus travel distance wouldn't affect their foraging decisions when collecting nectar to feed themselves.  When foraging for their young, they collect insects which are lightweight relative to the male's weight.  Under these conditions, they should increase their load of insects as travel distance increases, which is the opposite of what the Max. E Efficiency model predicts.