Passage Reading and English Comprehension

Although numbers of animals in a given region may fluctuate from year to year, the fluctuations are often temporary and, over long periods, trivial. Scientists have advanced three theories of population control to account for this relative constancy.

The first theory attributes a relatively constant population to periodic climatic catastrophes that decimate populations with such frequency as to prevent them from exceeding some particular limit. In the case of small organisms with short life cycles, climatic changes need not be catastrophic: normal seasonal changes in photoperiod (daily amount of sunlight), for example, can govern population growth. This theory—the density-independent view—asserts that climatic factors exert the same regulatory effect on population regardless of the number of individuals in a region.

A second theory argues that population growth is primarily density-dependent—that is, the rate of growth of a population in a region decreases as the number of animals increases. The mechanisms that manage regulation may vary. For example, as numbers increase, the food supply would probably diminish, which would increase mortality. In addition, as Lotka and Volterra have shown, predators can find prey more easily in high-density populations. Other regulators include physiological control mechanisms: for example, Christian and Davis have demonstrated how the crowding that results from a rise in numbers may bring about hormonal changes in the pituitary and adrenal glands that in turn may regulate population by lowering sexual activity and inhibiting sexual maturation. There is evidence that these effects may persist for three generations in the absence of the original provocation. One challenge for density-dependent theorists is to develop models that would allow the precise prediction of the effects of crowding.

A third theory, proposed by Wynne-Edwards and termed “epideictic,” argues that organisms have evolved a “code” in the form of social or epideictic behavior displays, such as winter-roosting aggregations or group vocalizing; such codes provide organisms with information on population size in a region so that they can, if necessary, exercise reproductive restraint. However, Wynne-Edwards’ theory, linking animal social behavior and population control, has been challenged, with some justification, by several studies.

179. The primary purpose of the passage is to

	(a) argue against those scientists who maintain that animal populations tend to fluctuate
	(b) compare and contrast the density-dependent and epideictic theories of population control
	(c) provide example of some of the ways in which animals exercise reproductive restraint to control their own numbers
	(d) summarize a number of scientific theories that attempt to explain why animal populations do not exceed certain limits

180. It can be inferred from the passage that proponents of the density-dependent theory of population control have not yet been able to

	(a) use their theory to explain the population growth of organisms with short life cycles
	(b) reproduce the results of the study of Christian and Davis
	(c) explain adequately why the numbers of a population can increase as the population’s rate of growth decreases
	(d) make sufficiently accurate predictions about the effects of crowding

181. Which of the following, if true, would best support the density-dependent theory of population control as it is described in the passage?

	(a) As the number of foxes in Minnesota decrease, the growth rate of this population of foxes begins to increase.
	(b) As the number of woodpeckers in Vermont decreases, the growth rate of this population of woodpeckers also begins to decrease.
	(c) As the number of prairie dogs in Oklahoma increases, the growth rate of this population of prairie dogs also begins to increase.
	(d) After the number of beavers in Tennessee decreases, the number of predators of these beavers begins to increase.

182. According to the Wynne-Edwards theory as it is described in the passage, epideictic behavior displays serve the function of

	(a) determining roosting aggregations
	(b) locating food
	(c) attracting predators
	(d) regulating sexual activity

183. The challenge posed to the Wynne-Edwards-theory by several studies is regarded by the author with

	(a) complete indifference
	(b) qualified acceptance
	(c) skeptical amusement
	(d) perplexed astonishment

184. Which of the following statements would provide the most of logical continuation of the final paragraph of the passage?

	(a) Thus Wynne-Edwards’ theory raises serious questions about the constancy of animal population in a region.
	(b) Because Wynne-Edwards’ theory is able to explain more kinds of animal behavior than is the density-dependent theory, epideictic explanations of population regulation are now widely accepted.
	(c) The results of one study, for instance, have suggested that group vocalizing is more often used to defend territory than to provide information about population density.
	(d) Some of these studies have, in fact, worked out a systematic and complex code of social behavior that can regulate population size.

TOTAL

Detailed Solution

1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20
21	22	23	24	25	26	27	28	29	30	31	32	33	34	35	36	37	38	39	40
41	42	43	44	45	46	47	48	49	50	51	52	53	54	55	56	57	58	59	60
61	62	63	64	65	66	67	68	69	70	71	72	73	74	75	76	77	78	79	80
81	82	83	84	85	86	87	88	89	90	91	92	93	94	95	96	97	98	99	100
101	102	103	104	105	106	107	108	109	110	111	112	113	114	115	116	117	118	119	120
121	122	123	124	125	126	127	128	129	130	131	132	133	134	135	136	137	138	139	140
141	142	143	144	145	146	147	148	149	150	151	152	153	154	155	156	157	158	159	160
161	162	163	164	165	166	167	168	169	170	171	172	173	174	175	176	177	178	179	180
181	182	183	184	185	186	187	188	189	190	191	192	193	194	195	196	197	198	199	200
201	202	203	204	205	206	207	208	209	210	211	212	213	214	215	216	217	218	219	220
221	222	223	224	225	226	227	228	229	230	231	232	233	234	235	236	237	238	239	240
241	242	243	244	245	246	247	248	249	250	251	252	253	254	255	256	257	258	259	260
261	262	263	264	265	266	267	268	269	270	271	272	273	274	275	276	277	278	279	280
281	282	283	284	285	286	287	288	289	290	291	292	293	294	295	296	297	298	299	300
301	302	303	304	305	306	307	308	309	310	311	312	313	314	315	316	317	318	319	320
321	322	323	324	325	326	327	328	329	330	331	332	333	334	335	336	337	338	339	340
341	342	343	344	345	346	347	348	349	350	351	352	353	354	355	356	357	358	359	360
361	362	363	364	365	366	367	368	369	370	371	372	373	374	375	376	377	378	379	380
381	382	383	384	385	386	387	388	389	390	391	392	393	394	395	396	397	398	399	400
401	402	403	404	405	406	407	408	409	410	411	412	413	414	415	416	417	418	419	420
421	422	423	424	425	426	427	428	429	430	431	432	433	434	435	436	437	438	439	440
441	442	443	444	445	446	447	448	449	450	451	452	453	454	455	456	457	458	459	460
461	462	463	464	465	466	467	468	469	470	471	472	473	474	475	476	477	478	479	480
481	482	483	484	485	486	487	488	489	490	491	492	433	494	495	496	497	498	499	500

Passage Reading Verbal Logic Non Verbal Logic Numerical Logic Data Interpretation Reasoning Analytical Ability Basic Numeracy About Us Contact Privacy Policy Major Tests FAQ

---