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Using 18 years of census data from permanent quadrats, we examined the interactions between spatially coexisting but temporally
segregated winter and summer ephemeral plant communities in the Chihuahuan Desert. The ability of winter and summer annuals
to achieve nearly complete temporal segregation by partitioning the bimodal annual rainfall permits the coexistence of a diverse
flora of annual (and perennial) plants in this unproductive arid environment. Despite the differences in their biogeographical
affinities and temporal segregation, long-term data indicated that at the scales of both the entire 20-ha study site and small
0.25-m2 sample quadrats, abundances of plants were never high in two successive growing seasons, suggesting a negative interaction
between winter and summer annuals. We evaluate alternative hypotheses for this phenomenon.
Received: 22 February 1996 / Accepted: 16 September 1996 相似文献
3.
Sarah H. Peterson Joshua T. Ackerman Mark P. Herzog C. Alex Hartman Rebecca Croston Cliff L. Feldheim Michael L. Casazza 《Ecology and evolution》2019,9(9):5490-5500
For ground‐nesting waterfowl, the timing of egg hatch and duckling departure from the nest may be influenced by the risk of predation at the nest and en route to wetlands and constrained by the time required for ducklings to imprint on the hen and be physically able to leave the nest. We determined the timing of hatch, nest departure, and predation on dabbling duck broods using small video cameras placed at the nests of mallard (Anas platyrhynchos; n = 26), gadwall (Mareca strepera; n = 24), and cinnamon teal (Anas cyanoptera; n = 5). Mallard eggs began to hatch throughout the day and night, whereas gadwall eggs generally started to hatch during daylight hours (mean 7.5 hr after dawn). Among all species, duckling departure from the nest occurred during daylight (98%), and 53% of hens typically left the nest with their broods 1–4 hr after dawn. For mallard and gadwall, we identified three strategies for the timing of nest departure: (a) 9% of broods left the nest the same day that eggs began to hatch (6–12 hr later), (b) 81% of broods left the nest the day after eggs began to hatch, and (c) 10% of broods waited 2 days to depart the nest after eggs began to hatch, leaving the nest just after the second dawn (27–42 hr later). Overall, eggs were depredated at 10% of nests with cameras in the 2 days prior to hatch and ducklings were depredated at 15% of nests with cameras before leaving the nest. Our results suggest that broods prefer to depart the nest early in the morning, which may best balance developmental constraints with predation risk both at the nest and en route to wetlands. 相似文献
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Odour-mediated responses of phytophagous mites to conspecific and heterospecific competitors 总被引:8,自引:0,他引:8
Plants under herbivore attack produce volatiles, thus attracting natural enemies of the herbivores. However, in doing so,
the plant becomes more conspicuous to other herbivores. Herbivores may use the odours as a cue to refrain from visiting plants
that are already infested, thereby avoiding competition for food, or, alternatively, to visit plants with defences weakened
by earlier attacks. We investigated the response of one species of herbivore (the spider mite Tetranychus urticae) to odours emanating from cucumber plants infested by conspecific or heterospecific (the western flower thrips, Frankliniella occidentalis) herbivores. Olfactometer experiments in the laboratory showed that spider mites have a slight, but significant, preference
for plants infested with conspecifics, but strongly avoid plants with thrips. These results were substantiated with greenhouse
experiments. We released spider mites on the soil in the centre of a circle of six plants, half of which were infested with
either conspecifics or heterospecifics (thrips), whereas the other half were uninfested. It was found that 60–70% of the mites
were recaptured on the plants within 5 h after release. Results of these experiments were in agreement with results of the
olfactometer experiments: (1) significantly fewer spider mites were found on plants infested with thrips than on uninfested
plants and (2) more mites were found on plants with conspecifics than on clean plants (although this difference was not significant).
From a functional point of view it makes sense that spider mites prefer clean plants over thrips-infested plants, since thrips
are not only competitors, but are also known as intraguild predators of spider mites. Possible reasons for the slight attraction
of spider mites to plants infested with conspecifics are discussed.
Received: 22 June 1996 / Accepted: 29 September 1996 相似文献
6.
Interference competition by aggressive foraging often explains resource partitioning, but mechanisms contributing to partitioning
have rarely been studied in Asian social bee guilds. Foraging of social bees at canopy flowers of Santiria laevigata (Burseraceae) and honey-water feeders was studied in a lowland mixed-dipterocarp forest in Sarawak, Malaysia. Four stingless
bee species (Apidae, Meliponinae), Trigona canifrons, T.␣fimbriata, T. apicalis and T. melina, aggressively defended flower patches and feeders. At the flowers, T.␣canifrons excluded other bees only in the morning when nectar flow peaked. At the feeders, the aggression resulted in asymmetric interference
competition, which produced a dominance hierarchy among seven social bee species. Interspecific partitioning of the feeders
was detected in time and height but not quality. Only time of the first arrival after feeder presentation was negatively correlated
with the dominance hierarchy: more aggressive species arrived at the feeders later than less aggressive species. This result
suggests that a trade-off between searching ability and defensive ability at flower patches gives rise to resource partitioning
in the social bee guild.
Received: 22 June 1996 / Accepted: 22 November 1996 相似文献
7.
Stephen F. Matter 《Oecologia》1997,110(4):533-538
The relationship between population density and the size of host plant patches was investigated for the red milkweed beetle
Tetraopestetraophthalmus inhabiting unmanipulated patches of Asclepias syriaca. The resource concentration hypothesis proposes that density-area patterns, specifically that of increasing herbivore density
with patch size, are primarily a function of movement between host plant patches. This research investigated the degree to
which movement accounted for density-area patterns. Poisson regression analysis of beetle abundance versus milkweed patch
size revealed that beetle density tended to increase with patch size. The pattern of density and patch size resulted from
local reproduction and residence time. The density of emerging beetles tended to increase with patch size while emigration
rates were unrelated to patch size. Immigration rates were constant with patch size for male beetles, and decreased with patch
size for female beetles. Net flux of beetles (immigration – emigration) did not vary with patch size for male beetles and
decreased with patch size for female beetles. Comparisons are made between this system and previously studied systems where
movement plays a significant role in forming density area patterns. Additionally, several hypotheses are presented which may
account for greater in situ recruitment and residence time in large patches.
Received: 23 February 1996 / Accepted: 8 January 1997 相似文献
8.
John L. Maron 《Oecologia》1997,110(2):284-290
Seedlings suffer high mortality in most plant populations, with both competition and herbivory proposed as being important
mechanisms causing seedling death. The relative strength of these factors, however, is often unknown. Here I ask how interspecific
competition for light and insect herbivory jointly affect seedling survival of bush lupine (Lupinus arboreus), a native shrub common to coastal California. Bush lupine seedlings germinate in grasslands during winter, and throughout
spring potentially compete for light with surrounding fast-growing annual grasses. By early summer, after grasses have died,
seedlings can be defoliated by a locally abundant caterpillar, the western tussock moth (Orgyia vetusta). I examined the relative importance of competition and insect herbivory on seedling survival in two separate experiments.
First, I compared seedling mortality in plots either exposed to or protected from tussock moth larvae. Plants were protected
from herbivory by the judicious use of insecticide; control plants were sprayed with water. Tussock moth herbivory resulted
in significantly greater (31%) seedling mortality. To determine the effects of interspecific competition for light on seedling
survival, I manipulated the density of grass surrounding lupine seedlings. I removed all vegetation surrounding some individuals,
and left intact vegetation surrounding others. Reducing competition resulted in a 32% increase in seedling survival from February
to June, as well as changes in seedling growth. To determine whether there are interactive effects of competition and herbivory
on seedling survival, I enclosed tussock moth larvae on half of all surviving seedlings within each of the two prior competition
treatments, comparing growth and survival of defoliated and undefoliated seedlings. Defoliation in June led to an additional
50% mortality for individuals that had grown with competitors through spring, and a 53% additional mortality for seedlings
that grew without competitors through spring. Thus, although competition and herbivory both caused substantial seedling mortality,
there was no statistical interaction between these factors. Competition-free plants were not less vulnerable to herbivory
than plants that previously grew with competitors. Taken together, these experiments indicate that competition and herbivory
are both important sources of mortality for bush lupine seedlings.
Received: 4 April 1996 / Accepted: 5 November 1996 相似文献
9.
Gregory S. Larsen S. Faith Frazier Sasha N. Zill 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(6):683-700
Many types of sense organs have been demonstrated to show repetitive discharges during walking that could provide informational
cues about leg movements and other parameters of locomotion. We have recorded activities of receptors of the distal (tarsal)
segments of the cockroach hindleg in restrained and freely moving animals while they were videotaped. These recordings show
peaks of activities at the onset and termination of the stance phase. We have morphologically and physiologically identified
a joint angle receptor, the tarso-pretarsal chordotonal organ, that contributes to the discharges seen late in stance, prior
to the onset of leg flexion in swing. This sense organ encodes the angle and rate of change of the most distal leg joint and
specifically discharges when the claws are disengaged from the substrate. Applied displacements of the claws in restrained
preparations elicit reflex activation of the tibial flexor muscle and a crossed extensor reflex in the opposite hindleg. These
reflexes could function to insure that leg flexion in swing does not occur until the claws are disengaged and to enhance support
by the opposite hindleg. Thus, the regular discharges of the chordotonal organ could assure efficient and coordinated muscle
contractions and movements during normal, unperturbed walking.
Accepted: 2 January 1997 相似文献
10.
D. J. Hosken P. C. Withers 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(1):71-80
The thermal and metabolic physiology of Chalinolobus gouldii, an Australian vespertilionid bat, was studied in the laboratory using flow-through respirometry. Chalinolobus gouldii exhibits a clear pattern of euthermic thermoregulation, typical of endotherms with respect to body temperature and rate of
oxygen consumption. The basal metabolic rate of euthermic Chalinolobus gouldii is approximately 86% of that predicted for a 17.5-g mammal and falls into the range of mass-specific basal metabolic rates
ascribed to vespertilionid bats. However, like most vespertilionid bats, Chalinolobus gouldii displays extreme thermolability. It is able to enter into torpor and spontaneously arouse at ambient temperatures as low
as 5 °C. Torpid bats thermoconform at moderate ambient temperature, with body temperature ≈ ambient temperature, and have
a low rate of oxygen consumption determined primarily by Q
10 effects. At low ambient temperature (< 10 °C), torpid C. gouldii begin to regulate their body temperature by increased metabolic heat production; they tend to maintain a higher body temperature
at low ambient temperature than do many northern hemisphere hibernating bats. Use of torpor leads to significant energy savings.
The evaporative water loss of euthermic bats is relatively high, which seems unusual for a bat whose range includes extremely
arid areas of Australia, and is reduced during torpor. The thermal conductance of euthermic C. gouldii is less than that predicted for a mammal of its size. The thermal conductance is considerably lower for torpid bats at intermediate
body temperature and ambient temperature, but increases to euthermic values for torpid bats when thermoregulating at low ambient
temperature.
Accepted: 22 August 1996 相似文献
11.
In this study we used pinfish (Lagodon rhomboides) in field experiments to examine linkages between intertidal saltmarsh and adjacent subtidal habitats. Pinfish are more
than twice as abundant in intertidal marshes adjacent to seagrass beds than in those adjacent to the unvegetated subtidal
bottom. Movement of pinfish between the marsh edge and the adjacent subtidal habitat was greater for fish captured in areas
with both intertidal and subtidal vegetation than in those with intertidal vegetation and adjacent unvegetated mudflats. This
movement provides an important link between habitats, allowing transfer of marsh-derived secondary production to subtidal
seagrass beds and vice versa. Pinfish held in enclosures with both intertidal and subtidal vegetation were, on average, approximately
90% heavier than fish held in enclosures with intertidal vegetation and unvegetated subtidal bottom. Because saltmarshes and
seagrass beds contribute to the production of living marine resources, active measures are being taken to preserve and restore
these habitats. The results from this study have direct application to decisions concerning site selection and optimal spatial
proximity of saltmarsh and seagrass habitats in the planning of restoration and mitigation projects. To maximize secondary
production and utilization of intertidal marshes, managers may opt to restore and/or preserve marshes adjacent to subtidal
seagrass beds.
Received: 31 May 1996 / Accepted: 23 October 1996 相似文献
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In some species of hagfish, the phenomenon of chromosome elimination occurs during embryogenesis. However, only two repetitive
DNA families are known to be represented in chromosomes that are eliminated from somatic cells of the Japanese hagfish Eptatretus okinoseanus. Using molecular analyses, another germ line-restricted, highly repetitive DNA family has been detected in another Japanese
hagfish, Paramyxine atami. The repeat unit of this family, which is 83 bp long, has been designated “EEPa1”, for Eliminated Element of P. atami 1. DNA filter hybridization using EEPa1 as a probe revealed that this family is shared among several species and is conserved
in the germline DNA. Although eliminated, repetitive DNA that is shared interspecifically has not been reported in hagfish
species, cases of chromatin diminution and chromosome elimination processes have been described previously in other organisms.The
patterns and intensities of hybridization signals suggest that members of the repetitive DNA family defined by EEPa1 have
undergone concerted molecular evolution.
Received: 7 January 1997 / Accepted: 13 May 1997 相似文献
14.
B. Hedwig R. Heinrich 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(3):285-294
During courtship sequences male grasshoppers of the species Omocestus viridulus successively perform with their hindlegs three different stridulatory movement patterns: ordinary stridulation, hindleg shaking
and precopulatory movements. Microinjection of acetylcholine into protocerebral neuropil regions can either elicit complete
courtship sequences or evoke one of the three motor patterns. Intracellular recordings and stainings revealed three types
of descending brain neurons: B-DC-3, B-DC-4 and B-DC-5. All three types of interneurons have a medial axon position in the
connectives. They cross the midline of the protocerebrum and exhibit a profuse arborization pattern within the medial dorsal
protocerebral neuropil. Stimulation of each type of interneuron specifically elicits one particular motor pattern of courtship
behaviour. Courtship of the grasshopper O. viridulus may therefore be controlled by successive activation of these descending brain neurons.
Accepted: 27 September 1996 相似文献
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P. Meier J. Zettel 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(4):297-304
In the Swiss Prealps Entomobrya nivalis hibernates in an inactive state, hidden under bark flakes on spruce. For freeze avoidance it relies on thermal hysteresis
proteins (THPs) and polyols (mainly ribitol, with small amounts arabitol and threitol). Polyols are present only during the
inactive state, THPs additionally protect during the transition phase in spring and autumn, when animals are still active
but frosts may occur. Peak values were recorded in February/March for THPs (3.5 °C hysteresis between melting and freezing
point) and for polyols (26 μg mg−1 FW; hemolymph osmolality 680 mosmol l−1). E. nivalis is able to control its hemolymph osmolality independently of body water content. Mean osmolality in summer was 350– 440 mosmol l−1, in winter it was elevated to 650 mosmol l−1, due to a synthesis mainly of ribitol. Body water content varied between 1.8 and 3.3 mg H2O mg−1 DW, depending on humidity conditions. Experiments on triggering of antifreeze synthesis showed the action of temperature
and photoperiod as cues, but there was also evidence for an endogenous rhythm. No clear correlation between antifreeze concentration
and supercooling ability could be established, suggesting that gut content or other parameters also play an inportant role.
Accepted: 18 November 1995 相似文献
17.
Brassica oleracea L. is highly polymorphic and includes varieties which exhibit a headed phenotype (a large preinflorescence): the curd of
cauliflower and `romanesco' (var. botrytis), and the spear of broccoli (var. italica). This headed phenotype results from highly iterative patterns of activity at the primary meristems. Differences in the morphology
of curds and spears are accounted for by three quantitative variables: the rate of production of branch primordia on the flanks
of the apical meristems (RPP); the number of branch primordia produced before the first formed begin producing their own branch
primordia (the iteration interval, ITI); and the duration of the preinflorescence stage (before production of flower primordia).
Relatively stable iteration parameters (RPP and ITI) during curd development lead to the production of semi-spherical curds
with a smooth surface in cauliflower and broccoli, whereas in `romanesco' RPP and ITI increase throughout curd development,
inducing a pyramidal curd with an angular surface. A relatively long preinflorescence stage in cauliflower and `romanesco'
results in the curd surface being composed largely of branch primordia, whereas in broccoli this stage is short and the spear
surface is made up of flower buds. Simplified growth models for these three headed types are presented. The implications for
the genetic control of the B. oleracea L. headed phenotype and the relationships between shoot apical meristem size, phyllotaxis and curd/spear morphology are discussed.
Received: 11 September 1997 / Accepted: 12 November 1997 相似文献
18.
Micky D. Eubanks Kimberly A. Nesci Mette K. Petersen Zhiwei Liu Horacio Bonfil Sanchez 《Oecologia》1997,109(3):454-460
Larvae of a Polyhymno species (Lepidoptera: Gelechiidae) feed on the ant-defended acacia, Acacia cornigera, in the tropical lowlands of Veracruz, Mexico. Polyhymno larvae construct sealed shelters by silking together the pinna or pinnules of acacia leaves. Although larval density and
larval survival are higher on acacias not occupied by ants, shelters serve as a partial refuge from the ant Pseudomyrmex ferruginea (Hymenoptera: Formicidae), which defends A. cornigera plants; thus, shelters provide Polyhymno larvae access to an ant-defended host plant. P. ferruginea ants act as the primary antiherbivore defense of A. cornigera plants, which lack the chemical and mechanical defenses of non-ant-defended acacias. Thus, defeating the ant defense of A. cornigera provides Polyhymno larvae access to an otherwise poorly defended host plant. Damage caused by Polyhymno larval feeding reaches levels which can kill A. cornigera plants.
Received: 6 June 1996 / Accepted: 6 September 1996 相似文献
19.
Fish species richness and incidence patterns in isolated and connected stream pools: effects of pool volume and spatial position 总被引:4,自引:0,他引:4
Christopher M. Taylor 《Oecologia》1997,110(4):560-566
I tested the effects of pool size and spatial position (upstream or downstream) on fish assemblage attributes in isolated
and connected pools in an upland Oklahoma stream, United States. I hypothesized that there would be fundamental differences
between assemblages in these two pool types due to the presence or absence of colonization opportunities. Analyses were carried
out at three ecological scales: (1) the species richness of pool assemblages, (2) the species composition of pool assemblages,
and (3) the responses of individual species. There were significant species-volume relationships for isolated and connected
pools. However, the relationship was weaker and there were fewer species, on average, in isolated pools. For both pool types,
species incidences were significantly nested such that species-poor pools tended to be subsets of species-rich pools, a common
pattern that ultimately results from species-specific differences in colonization ability and/or extinction susceptibility.
To examine the potential importance of these two processes in nestedness patterns in both pool types, I made the following
two assumptions: (1) probability of extinction should decline with increasing pool size, and (2) probability of immigration
should decline in an upstream direction (increasing isolation). When ordered by pool volume, only isolated pools were significantly
nested suggesting that these assemblages were extinction-driven. When ordered by spatial position, only connected pools were
significantly nested (more species downstream) suggesting that differences in species-specific dispersal abilities were important
in structuring these assemblages. At the individual-species level, volume was a significant predictor of occurrence for three
species in isolated pools. In connected pools, two species showed significant position effects, one species showed a pool
volume effect, and one species showed pool volume and position effects. These results demonstrate that pool size and position
within a watershed are important determinants of fish species assemblage structure, but their importance varies with the colonization
potential of the pools. Isolated pool assemblages are similar to the presumed relaxed faunas of montane forest fragments and
land bridge islands, but at much smaller space and time scales.
Received: 6 December 1996 / Accepted: 10 December 1996 相似文献