Chapter 55

1. (a) Mutualism (b) Amensalism (c) Parasitism (d) Competition

2. The conditions that can modify or change a two species interaction include physical conditions, biological processes such as dispersal, and other interacting species.

3. No, it is unlikely that the lionfish prey in the Atlantic have had enough time to adjust in an evolutionary way to their novel predator. This conclusion is supported by the data, which show that some reefs in the Atlantic have suffered a 65 percent decline in small-bodied coral-reef fish.

1. Perhaps the simplest behavior a reef fish might adopt—or that might evolve in reef fish—would be to avoid headfirst capture by the lionfish. This might involve adopting a way to detect a lionfish’s presence and fleeing the encounter before the predator could use jets to create a headfirst capture. Or after being hit by a jet of water, the prey could adopt unpredictable swimming movements to avoid headfirst capture.

2. Both herbivory and parasitism typically involve a symbiosis in which the herbivore or parasite is smaller than, and may live on, the plant or host. This close relationship naturally leads to species evolving specialized mechanisms that counter their effects on one another. In addition, the prey of herbivores are plants, which are immobile, and thus may also evolve special mechanisms in response to the potential for intense herbivory.

3. The number of grass species would be highest when the hare population is highest and lowest when the hare population is lowest.

1. A realized niche is defined by a species’ interactions with other species. The red squirrel’s realized niche has become smaller because of the competition with the gray squirrel.

2. Herbivory by the hares is the interaction that allows the grass species to coexist with one another. By grazing on the dominant grass species, the hares allow more subordinate grass species to thrive.

3. Scenario 1 is an example of exploitation competition because you and your friend are sharing the milkshake resource. Scenario 2 is an example of interference competition because your friend is excluding you from the milkshake resource.

1. An obligate mutualism would evolve when the two species involved in the interaction benefit from each other more than from other partners. A facultative mutualism would evolve when the two species involved in the interaction benefit from partnerships with multiple species. For example, if multiple species can deliver pollen or seeds to their desired locations, then facultative relationships will be more likely to evolve.

2. A-58

   Both species of barnacles are more likely to benefit from positive interactions under the more stressful conditions of the high intertidal where desiccation occurs.

3. Examples include trees, coral reefs, and kelp forests, where the habitat provided by these species facilitates many other species that depend on them.

1. The researchers used both methods to collect data for two different purposes. In the open aquarium trials, they wanted to observe the behavior of the lionfish and its prey in a relatively natural setting to see what strategies the lionfish used to capture and eat the prey. They learned that the lionfish would capture the prey when the prey turned and oriented its head toward the head of the lionfish. This headfirst orientation allowed the lionfish to more easily capture its prey.

   In the container trials, the researchers wanted to observe the behavior of the lionfish, particularly the production of water-jet pulses from its mouth, in a setting where the lionfish could see, but not capture or eat, the prey. In this way the researchers could measure the number of water jets produced and the maximum distance a water jet could travel, to get an idea of what behaviors a lionfish might employ when its prey was hard to catch (in this case, because the prey was in an inaccessible container).

2. Given that fish prey in the Atlantic Ocean are more naive to lionfish predatory behavior than fish prey in the Pacific Ocean, it would make sense that lionfishes would need to produce fewer and closer jets of water to capture their fish prey in the Atlantic Ocean compared with the Pacific Ocean. The Pacific Ocean fish should be harder to catch and thus require more water jets produced from a greater distance from the prey.

3. The field observations suggest that Pacific Ocean lionfishes need to resort to the water jet–blowing behavior to catch their prey more often than Atlantic Ocean lionfishes do. This pattern could be explained by the hypothesis that fish prey in the Atlantic Ocean are more naive to lionfishes and thus easier to catch. Atlantic Ocean fish prey are less likely to take appropriate evasive actions or require the use of the water jet–blowing behavior to confuse or disorient them. In addition, it is likely that the production of water jets is metabolically costly, and that lionfishes would use this behavior only when the cost of producing it is outweighed by the advantages it confers. Presumably this would be more likely to be the case for prey in the Pacific Ocean than for prey in the Atlantic Ocean.

1. Pollination is a positive interaction, or facilitation. Specifically, it is a mutualism, meaning both partners benefit. Bees obtain food (pollen and nectar) from plants. Plants rely on bees for pollination, which is necessary for successful reproduction. For a successful pollination interaction, bees must emerge at the same time that plants flower.

2. Over time, the trend in bee pollination date is slightly downward, indicating that the bees were pollinating slightly earlier in the year. The mean April temperature showed an upward trend, indicating that temperatures rose over the time period. The opposing directions of the trends indicate that as temperatures rose, bees were pollinating earlier in the year. The steeper slope after 1970 on both graphs suggests that temperature has increased faster since 1970. Statistical analysis bears this out; 69 percent of the bees’ advance in pollination activity has occurred since 1970.

3. The recent study (1971–1999) shows plant flowering advancing faster than bee pollination dates, and thus best supports the hypothesis that climate warming is affecting plant-pollinator interactions by creating mismatches in the timing of these events.

4. Specialist plant–pollinator interactions are more likely to be affected by timing mismatches caused by rising temperatures. Generalist species (such as those in these studies) can rely on many species for food or pollination interactions; if one or several species pairs show timing mismatches, other species will likely be present to participate in the interaction. Specialist pairs, which depend on only one or a few species, are far more susceptible to the effects of timing mismatches. If timing mismatches occur, there may be no species available to interact with.

5. There are many possible designs, but more precise information would require analysis of specific plant–pollinator pairs, rather than the generalized groups in the current studies. The study would require seasonal measurements of plant flowering dates and pollinator emergence and pollination activity dates (as opposed to collection dates) for several years, correlated directly with climate data. Ideally studies should focus on pairs for which background information is already available on past emergence and flowering dates. Good candidates would include pollinators of important crop plants, such as apple trees or tomatoes.