46. El Niño events
(A) occur when the Southern Oscillation index is high.
(B) occur when barometric pressure is lower in the western Pacific than in the eastern Pacific.
(C) include the appearance of warm currents on the Pacific coast of South America.
(D) are always accompanied by La Niña events at the same time.
(E) are accompanied by westward movement of the location of storm generation in the Pacific.

42. ________species are those that, despite low biomass, exert strong effects on community structure. (A) Keystone (B) Cornerstone (C) Dominant (D) Prominent (E) Foundational

43. The equilibrium model of island biogeography explains diversity on islands as a balance between (A) speciation and extinction. (B) immigration and extinction. (C) speciation and emigration. (D) immigration and emigration. (E) speciation and immigration.

44. The study of the relationship between climate and the timing of ecological events is called (A) ecology. (B) phenology. (C) succession. (D) climatology. (E) life history theory.

45. In general, reptiles are considered to be a/an . (A) poikilotherm (B) homeotherm (C) endotherm (D) heterotherm (E) A and D are correct

47. Mycorrhizal fungi (directly) help their plant partners acquire (A) sugars. (B) sunlight. (C) seed dispersal. (D) soil nutrients. (E) pollination.

48. dN/dt = rmaxN [(K – N)/K] represents (A) annual growth rate. (B) geometric population growth. (C) exponential growth rate. (D) logistic growth. (E) none of the choices are correct.

49. Bony marine fish (A) drink sea water. (B) secrete Na+ into the surrounding water. (C) are hyperosmotic compared to the surrounding water. (D) both drink sea water and secrete Na+ into the surrounding water. (E) drink sea water, secrete Na+ into the surrounding water, and are hyperosmotic compared to the surrounding water.

50. Whether during mitosis or meiosis, sister chromatids are held together by proteins referred to as cohesions. Such molecules must have which of the following properties? (A) They must reattach to chromosomes during G1. (B) They must be removed before anaphase can occur. (C) They must be intact for nuclear envelope reformation. (D) They must be removed before meiosis can begin. (E) They must persist throughout the cell cycle.

51. Analysis of the Lotka-Volterra competition model implies that two competitors can coexist only when (A) interspecific competition is stronger than intraspecific competition. (B) intraspecific competition is stronger than interspecific competition. (C) intraspecific and interspecific competition are equally strong. (D) predation or parasitism is stronger than interspecific competition. (E) actually, the model implies that two competitors can never coexist. 

52. Mouse mutations can affect an animal's appetite and eating habits. The ob gene produces a satiety factor (the hormone leptin). The db gene product is required to respond to the satiety factor (the leptin receptor). Most obese humans produce normal or increased levels of leptin without satiety. Which might provide an answer to at least some human obesity if a means to do so is found? (A) overexpression of the leptin receptor gene (B) activation of receptors for leptin (C) supplementary leptin (D) inactivation of leptin (E) mutation of the leptin receptor gene