Exam 15: Mutualism and Commensalism

Scientists have studied the value of positive interactions in ecosystems by measuring the "relative neighbor effect" (RNE), or the effect that neighboring species have on the growth of a target species. Given the usual purposes of positive interactions, in which ecosystem would the neighboring plant species be most likely to help a target species?

Acacia plants often have ants of the genus Pseudomymex associated with them. Removal of ant colonies from individuals of the bullhorn acacia species results in which change in the acacias?

Cord grass is a major plant in saltmarshes in southeastern United States. It provides habitat for many saltmarsh species, such as snails, crabs, conch, and mullet. Within these species, cord grass could best be described as a

The studies by Pellmyr and Huth on yuccas and yucca moths showed that

Refer to the figure. The figure shows the influence of soil temperature on the interaction between two wetland plants, forget-me-nots and cattails. Cattails have extensive air channels for transporting oxygen in their leaves, stems, and roots. Forget-me-nots lack air channels. Based on the figure, as soil temperature increased, the influence of cattails on the growth of forget-me-nots changed from

An ant colony maintains and farms a species of fungus on which it feeds. The fungus, in turn, is parasitized by a bacterium. The ant/fungus interaction is _______ and the fungus/bacterium is _______.

Refer to the table. The table contains data on the effects of a symbiosis between a bee (host) and a bacterium over 22 years. The table shows the upper and lower bounds for the effects of the association; positive numbers denote net benefits and negative numbers denote net costs. (If zero is between the upper and lower bounds, consider the effect to be zero, since it is statistically indistinguishable from zero.) According to the table, this interaction first become a commensalism in

A seedling begins to grow very close to a leaf-cutter ant colony. What is a possible cost or benefit of growing in that area?

For an ecological interaction to be a mutualism, the net benefits must

Refer to the figure. Medicago truncatula, or barrelclover, is a clover-like legume that has a mutualistic association with mycorrhizal fungi. In the experiment illustrated in the figure, fungi in contact with Medicago had access to either no phosphorus, or to either 35 or 700 ?M of phosphorus. According to the figure, how did Medicago alter the amount of carbohydrate it transferred to the fungi in response to the change in fungal phosphorus levels?

Refer to the figure. The RNE (relative neighbor effect) measures growth of a target plant species in the presence and absence of neighboring species. The figure shows graphs of the RNE at eleven sites around the world. RNE was measured at high and at low elevations at each site. RNE values above zero (blue) indicate that neighboring plants increased the growth of target species; RNE values below zero (red) indicate that neighbors decreased target species growth. -This study showed that the presence of neighboring plants most often benefited the target plants at

In a prairie ecosystem, mycorrhizal fungi form associations with the roots of prairie grasses, such as big bluestem. When the mycorrhizae are removed, the performance of big bluestem decreases, while the performance of other prairie grasses and wildflowers increases. This effect most clearly shows the influence of mutualisms on

What characteristics are found in Pseudomyrmex ants that depend on acacias, compared to species of Pseudomyrmex that are not associated with acacias?

Yucca plants retain 62% of the flowers that contain up to six moth eggs, but only 11% of the flowers containing nine or more eggs. The yucca aborts these flowers before the moth eggs hatch. This process is only effective for reducing exploitation by moths if

Humans have associated with canines throughout history, and this has led to the emergence of domestic dogs. Historically, dogs helped humans defend their livestock and aided in hunting. Create a table (Table 1) that includes the following terms: symbiotic, mutualism, commensalism, parasitic, obligate/facultative, trophic mutualism, habitat mutualism, and service mutualism. Describe each term's applicability and justification in regard to the historic human/dog relationship.

The loss of mycorrhizae-plant associations, in both angiosperms and gymnosperms, would have which effect on the plants?

Grutter tested the effect of cleaner fish on species diversity in the Great Barrier Reef by

You are studying two new species that have a mutualistic relationship. How would you determine if the mutualism is facultative or obligate? What types of observational data would you collect and what type of experiment would you conduct?

Refer to the table. The table contains data on the effects of symbiosis between a fly (host) and a fungus over many years. It shows the upper and lower bounds for the effects of the association; positive numbers denote net benefits and negative numbers denote net costs. (If zero is between the upper and lower bounds, consider the effect to be zero, since it is statistically indistinguishable from zero.) -According to the table, in what year did the relationship between the fungus and the fly first become a mutualism?

Which statement describes the critical distinction between arbuscular mycorrhizae and ectomycorrhizae?