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1.
Increased energy expenditure due to increased territorial defense in male lizards after phenotypic manipulation 总被引:4,自引:0,他引:4
Catherine A. Marler Glenn Walsberg Myra L. White Michael Moore C. A. Marler 《Behavioral ecology and sociobiology》1995,37(4):225-231
Fitness tradeoffs are difficult to examine because many fitness variables are correlated and vary in the same direction. Phenotypic manipulation circumvents many of these difficulties, and here we used this technique to examine mechanisms for tradeoffs between increased aggression (territorial defense) and survivorship. The behavioral phenotype of male mountain spiny lizards (Sceloporus jarrovi) was manipulated with testosterone to increase territorial defense, a sexually selected trait. We previously demonstrated that increased territorial defense results in a decrease in survival caused by a lower ratio of energy intake to energy expenditure. Here we measured energy consumption of increased territorial aggression using the doubly labeled water technique in the field and compared males with and without testosterone implants (Fig. 1). In a supplementary study we measured standard metabolic rate using captive lizards given similar testosterone implants to examine if an increase in energy expenditure was a result of only an increase in standard metabolic rate (Fig. 3). Our results indicated that a primary contribution to tradeoffs between increased territorial defense and survivorship could be made by a 31% increase in energy expenditure in the field that is not due to an increase in standard metabolic rate. 相似文献
2.
Preference measures are widely used in habitat selection studies to test an animal’s choice relative to particular habitat
features, but most measures are subject to criticism as they fail to indicate the underlying behavioral motivation. Order
of settlement on breeding sites has been proposed as an effective measure in migratory organisms, as it conceptually approaches
a choice experiment. We tested the assumption that early red-backed shrikes (Lanius collurio) are more willing to defend their territorial resource than individuals arriving later. We earlier showed that shrikes arriving
first settled in forest plantations that resulted in lower reproductive success compared to territories on farmland, suggesting
an ecological trap. Therefore, individuals are expected to place higher value on the lower quality sites in forests. Within
the context of resource valuation theory in animal contests, we used a simulated territorial intrusion experiment to measure
territorial defense and to evaluate the perceived value of the territory during the settlement phase in both habitat types.
Males arriving early were much more motivated to defend their territory than late birds. After correction for the disparity
in the timing of arrival between habitat types, shrikes also more vigorously defended their territories in the forest habitat
associated with the lowest reproductive returns. Although some resource valuation mechanisms remain unclear, our results show
that early and late-arriving individuals strongly differ in behavioral motivation to hold their territorial resources. This
study also demonstrates for the first time that organisms may exhibit a higher degree of territorial aggressiveness in a lower
quality habitat. 相似文献
3.
Virtually all animal conflicts occur over access to mates or resources that affect survival, the two key components of fitness.
In this paper, we report that predation risk and mate defense jointly affect the outcomes of contests between male sand crabs
(Scopimera globosa) for burrows in which crabs mate and take shelter from predators. We observed the contests under three different conditions:
(1) the natural condition of low predation risk and without the presence of a female; (2) the first experiment in which we
imposed upon only intruding males the perception of predation risk—by digging them from their burrows, capturing and handling
them, and placing them into other males’ burrows—to increase the value of the burrows for the intruders as shelter, and (3)
the second experiment in which we repeated this treatment but increased the resource value of the burrow to the resident by
placing a female in his burrow. The difference in body size between contestants was the main determinant of victory in all
analyses. However, perceived predation risk also partly affected the outcomes of the fights: The motivated intruders were
likely to win even when they were a little smaller than the residents. In addition, defense of a female had a significant
effect on the outcomes of fights: The motivated residents won more fights than the motivated intruders, indicating that these
two treatments caused asymmetric increases of the resource value. This is the first report of two external factors simultaneously
raising resource value, affecting motivation of contestants, and altering the outcome of fights. 相似文献
4.
Cooperation in animal social groups may be limited by the threat of free riding, the potential for individuals to reap the benefits of other individuals actions without paying their share of the costs. Here we investigate the factors that influence individual contributions to group-level benefits by studying individual participation in territorial defense among female ringtailed lemurs (Lemur catta). To control for potentially confounding factors, particularly group size, we studied two semi-free-ranging groups at the Duke University Primate Center. First, we used a combination of experimental and observational methods to investigate the costs and benefits of territorial defense for individual lemurs. We found three indications of costs: physical contact occurred during inter-group encounters, participation in territorial defense was negatively correlated with ambient temperature, and rates of self-directed behaviors increased during encounters. Benefits were more difficult to quantify, but observational and experimental tests suggested that individuals shared the gains of territorial defense by foraging in defended territories. Thus, during experiments in which one of the groups was prevented from defending its territory, the free-ranging group made more frequent incursions into the other groups territory. Second, we examined variation in participation in territorial defense. Individuals varied significantly in their rates of aggression and genital marking during inter-group encounters. The extensive variation documented among individuals was partially accounted for by dominance rank, kinship and patterns of parental care. However, we found no evidence to suggest that participation was enforced through punishment (policing) or exchange of benefits involving grooming. In conclusion, this study provides further insights into cooperative behavior in mammalian social groups by revealing how the costs and benefits of territoriality influence patterns of individual participation in the context of shared (collective) goods.Communicated by P. Kappeler 相似文献
5.
E. J. Temeles 《Behavioral ecology and sociobiology》1989,24(4):239-243
Summary Food consumption may reduce fighting intensity of territory owners by decreasing resource value (additional food cannot be consumed) and/or increasing fighting costs (food in the digestive tract may raise injury risks). A territorial harrier's (Circus cyaneus, adult females) decision to reduce its level of aggression should depend upon whether or not the intruder was a competitor for individual prey items (as are smaller male floaters) or for the territory proper (as are female floaters and especially female neighbors). Accordingly, following meals, aggressive intensity of owners was strongly reduced towards male floaters (more were ignored), slightly reduced towards female floaters (more were called at than chased), and remained unchanged towards neighbors (virtually all were chased). Hence, alterations in aggressive behavior of territory owners following food consumption may depend upon the type of intruder and the resource under contest (a food item or a territory). 相似文献
6.
Henrik Pärn Karin M. Lindström Maria Sandell Trond Amundsen 《Behavioral ecology and sociobiology》2008,62(10):1665-1677
The optimal mating system is rarely the same for males and females—whereas males usually benefit from attracting additional
females to the territory, this could incur costs for the resident female. Females should therefore prevent prospecting females
from settling on the territory. We studied the male and female behavioral and hormonal responses to simulated female territorial
intrusions in free-living bluethroats during the pre-laying period. In the study population, polygyny occurs with potential
fitness costs for the resident female. We recorded different aspects of aggressive behavior before and after presentation
of a live female decoy and playback of female song. These behaviors were compared with a set of intrusions using a male decoy.
At the end of a trial, the birds were captured, and blood samples were analyzed for androstenedione, testosterone, estradiol
and corticosterone. During the pre-intrusion period, none of the females were observed. Females generally responded strongly
to the female decoy by increased flight rate, vocalizations, and by conspicuous perching. Nearly half of the males displayed
to the female decoy but never while the resident female was present. We suggest that resident female aggression in bluethroats
prevents courtship by her mate and signals her mating status to the female intruder. Female aggression could therefore prevent
additional females to settle on the territory and shape the mating system. Females that responded with song had higher levels
of estradiol. These findings suggest that estradiol may support aggression in breeding female birds. 相似文献
7.
Female choice and male–male aggression are two modes of sexual selection that can lead to elaboration of male morphological
and behavioral traits. In lek-mating species, male mating success is often strongly skewed, and it is puzzling why variation
in male traits is still observed given directional female choice. If male traits correlated with reproductive success are
honest signals of male quality, there may be survival costs associated with the expression of those traits. In this study,
we examined whether morphological, behavioral, and territorial traits are correlated with male mating success and survival
in the lek-mating greater prairie-chicken (Tympanuchus cupido). We introduce a novel application of multinomial discrete choice models for analysis of female mate choice behavior. We
found that behavioral and territorial attributes showed 6.5 times more variability among males than morphological traits.
Both display and aggressive behaviors were strong predictors of male mating success, suggesting that both female choice and
male–male aggression were important in determining mating success among male greater prairie-chickens. Moreover, annual survival
of male prairie-chickens was independent of mating success and male traits. Females appear to be choosing males based on behavioral
traits where large variation exists between males (coefficient of variation >30%). Behavioral traits were the most important
factor in determining mating success of male prairie-chickens, but the mechanism underlying this relationship is unknown.
In the future, experimental manipulations of male hormones or parasite loads could bridge the proximate mechanisms and ultimate
consequences of factors mediating male mating success in lek-mating grouse. 相似文献
8.
Genetic monogamy in the common loon (Gavia immer) 总被引:4,自引:0,他引:4
Walter H. Piper David C. Evers Michael W. Meyer Keren B. Tischler Joseph D. Kaplan Robert C. Fleischer 《Behavioral ecology and sociobiology》1997,41(1):25-31
We conducted behavioral observations and genetic analysis on breeding pairs of common loons in the upper Great Lakes region
from 1993 through 1995 to look for behavioral evidence of extrapair copulations (EPCs) and to determine parentage of young.
Pairs remained close to each other (usually within 20 m) during the pre-laying period, leaving little opportunity for EPCs
to occur. Males and females both maintained physical proximity by approaching each other when they became separated. Copulations
were obvious but infrequent, occurring about once every other day during the pre-laying period. Multilocus DNA fingerprinting
was consistent with behavioral findings: 58 young from 47 different families were all genetic offspring of parents that raised
them. Perfect genetic monogamy (genetic parentage of young by parents that rear them) in loons might arise as a consequence
of the need for vigorous territorial defense to prevent territorial takeover.
Received: 8 August 1996 / Accepted after revision: 22 March 1997 相似文献
9.
Frank Rosell Gry Gundersen Jean-François Le Galliard 《Behavioral ecology and sociobiology》2008,62(10):1559-1568
Neighbour–stranger discrimination occurs when individuals respond with more aggression to strangers than to territorial neighbours—a
phenomenon termed the “dear enemy phenomenon” (DEP). We investigated the DEP with male and female root voles (Microtus oeconomus Pallas 1776) using field dyadic arena tests conducted in enclosures where we could test for the effects of familiarity (familiar
versus stranger), ownership (resident versus intruder status) and resource-holding potential (body mass) on territorial behaviours.
The results showed that males put more effort into territorial defence than females, and males could discriminate between
neighbours and strangers. In males, aggressiveness was influenced by a significant two-way interaction between treatment and
ownership. Male residents were more aggressive towards stranger intruders than towards neighbour intruders, while male intruders
were less aggressive towards stranger residents than towards neighbour residents. In females, neither treatment nor ownership
status had a significant effect on aggressiveness. Familiar males performed more social behaviours but less non-social behaviours
than stranger males. Furthermore, there was a clear dominance hierarchy between residents and intruders in stranger dyads,
with the male territory holders dominating the intruder in pairwise interactions. To our knowledge, these results demonstrate
for the first time DEP in a small mammal with a known pedigree and present the first evidence for “prior resident advantage”
in voles. We argue that both ownership status and familiarity status affect how much an individual invests in territory defence.
The benefits of neighbour–stranger discrimination for male root voles and the absence of neighbour–stranger discrimination
in female root voles are discussed. 相似文献
10.
Vikram K. Iyengar Thomas Castle Sean P. Mullen 《Behavioral ecology and sociobiology》2014,68(2):275-282
Divergence of sexual signals in sympatry can arise as a consequence of (1) interspecific competition for resources, (2) selection against maladaptive hybridization, or (3) as a result of selection to reduce the cost of interspecific aggression; termed agonistic character displacement (ACD). Calopterygid damselflies have emerged as a model system for studying the evolution of divergent sexual signals due to the repeated evolution of sympatric species pairs with fully and partially melanized wings. Damselfly wing patterns function during both courtship and territory defense. However, the relative contributions of natural and sexual selection to phenotypic divergence and enhanced isolation in sympatry remain unclear in many cases. Here, we investigated the hypothesis that interference competition, in the form of increased interspecific male–male aggression, drives the evolution of character displacement in sympatry between two species of North American damselflies, Calopteryx aequabilis and Calopteryx maculata, that show no evidence of ecological divergence or ongoing hybridization. In paired behavioral trials, we found that interspecific male aggression related to territory defense varied between site, species, and as a function of the relative abundance of con- vs. hetero-specific males. Specifically, we found that large-spotted C. aequabilis males received increased intra- and interspecific aggression but that aggression against large-spotted males declined during the middle of the flight season when both species were equally abundant. Based on these results, we suggest that ACD leads to enhanced species recognition, and may be a common outcome of the antagonism between interspecific male–male competition and the countervailing force of intraspecific sexual selection favoring increased wing melanization among territorial damselfly species. 相似文献
11.
Non-market values were estimated with energy analysis under four land cover scenarios in the Ebro Delta, Spain. The market
value of agriculture, the primary use value, is compared. Conversion of the natural landscape to agricultural fields has resulted
in a drop in total annual non-market value from $721 million in the pristine scenario to $11 million in the present scenario.
The market value of the agricultural crops has risen over time, from $10 million to almost $52 million, contributing the major
portion of the total value of the Delta. However, the rate of return has decreased from the pristine to the present delta,
indicating that more energy is required to produce a smaller output. Energy analyses reveal that one form of value—non-market
value—is being traded for another—market value. 相似文献
12.
The establishment of dominance hierarchies through aggressive interactions is very common in insect societies. In many cases,
it is also mediated through pheromone emissions that enable individuals to evaluate the reproductive quality and level of
aggressiveness of the dominant individual, thereby reducing the number and intensity of costly fights. Here, we studied these
processes in the primitively eusocial bee Bombus terrestris, using a paired bee system. Specifically, we investigated the behavioral, reproductive, and pheromonal correlates of dominance
establishment. Workers were shown to establish dominance hierarchies using overt aggression within 3–4 days. Thereafter, the
aggression drastically decreased, and dominance was maintained mostly by ritualized agonistic behavior. The behaviorally dominant
bee lost the ester compounds that workers produce in their Dufour's gland (the so-called “sterility signal”) concomitantly
with the development of her ovaries. The other bee announced as subordinate by continuously producing high amounts of those
esters. The hypothesis that sterility signaling serves as an appeasement signal to pacify the dominant bees is supported by
the negative correlation found between the proportion of these esters and the level of aggression that the subordinate received
from the dominant worker. Physical interactions, and presumably also the ensuing overt aggression between the bees, were essential
for the above pheromonal change to take place and enabled the dominant workers to develop their ovaries and to lay eggs. The
subordinate bee’s signaling of non-reproductive status may minimize energy expenditure in costly fights and help stabilize
the reproductive division of labor among workers. 相似文献
13.
The giant panda (Ailuropoda melanoleuca) is notoriously difficult to study in the wild, but its interesting reproductive ecology makes the effort worthwhile. Perhaps
more than most species, the panda is energy-limited, which alters the cost/benefit analysis of its reproductive ecology. Using
global positioning system/very high frequency radiocollars to locate mating aggregations, we used behavioral observations
and fecal testosterone assays to gain insight into male panda reproductive effort and strategies, and test theories relating
to reproductive competition. Male pandas initially competed fiercely for access to females that were about to be fertile,
but once male competitive status was determined, aggression rates declined. Contact aggression was only observed during the
first 2 days of mating aggregations; thereafter, it was replaced with noncontact aggression and avoidance. Agonistic interactions
were highly asymmetrical, with contest losers (subordinates) showing less aggression and more avoidance than contest winners
(dominants), both before and after contest outcome was established. The competitively superior male displayed mate-guarding
tactics and secured all observed copulations. Contrary to theoretical predictions, testosterone levels did not predict aggression
levels or contest winners and also were not affected by winning or losing a contest. Body size appeared to be the primary
determinant of contest outcome. We discuss our findings in light of theoretical predictions, such as those arising from the
“challenge hypothesis,” in the context of the giant panda’s foraging and nutritional ecology. 相似文献
14.
Social facilitation of selective mortality 总被引:2,自引:0,他引:2
Territorial defense by breeders influences access to resources near defended nest sites by intruder species and may have indirect effects on other species within the territory, leading to local patchiness in distribution patterns. The present study demonstrates that adult males of a damselfish, Pomacentrus amboinensis, indirectly facilitate the increased survival of conspecific juveniles through the territorial defense of their nesting site from potential egg predators. Moreover, male territoriality results in a shift in the selectivity of predation on newly settled juveniles. We monitored the fate of pairs of predator-naive, newly settled P. amboinensis placed inside and outside nesting territories. Individuals within a pair differed in size by approximately 1 mm and were tagged for individual identification. Away from male territories larger juveniles had greater survival, while within territories, larger juveniles suffered higher mortality. Behavioral observations indicated that the moonwrasse Thalassoma lunare, a predator of benthic eggs and small fishes, had reduced access to juveniles within male territories, while another predator on small fishes, the dottyback Pseudochromis fuscus, had unobstructed access to male territories. Experimental removal of P. fuscus indicated that the shift in the direction of phenotypic selection on newly settled juveniles was the indirect effect of aggression by nest-guarding male damselfish, which resulted in differential access to male territories by these two predators of small fishes. Evidence suggests that behavioral interactions between the resident community and intruders will influence patchiness in selective pressures imposed on benthic prey by influencing both the composition of predator types that can access the prey resource and their relative abundance. How this spatial and temporal patchiness in predator pressure interacts with spatial patchiness of recruiting prey will have a major influence on the resulting distribution of juveniles and their phenotypic traits. 相似文献
15.
Natalie M. Sopinka Julie R. Marentette Sigal Balshine 《Behavioral ecology and sociobiology》2010,64(12):1947-1958
There is increasing concern for the disruptive effects seen in aquatic species exposed to environmental contaminants. However,
few studies have investigated the impact of such contaminants on the behavior of individuals living in exposed waters. Contaminant
exposure can affect animal populations by disrupting behaviors including feeding, locomotion, and mating. In this study, we
examined how living in an ecosystem polluted by combinations of polycyclic aromatic hydrocarbons, polychlorinated biphenyls,
and heavy metals (arsenic, cadmium, iron, lead, zinc) impacts contest behavior in the round goby (Neogobius melanostomus). Fish collected from heavily contaminated and cleaner sites in Lake Ontario were subjected to a resource contest to determine
the effect of these contaminants on aggression and the establishment of dominance hierarchies, which in turn influence access
to food, shelter, and mating opportunities. Dominance establishment (a clear resource winner) was less obvious among fish
from the contaminated site compared to the more stable hierarchies that formed between pairs of fish from the clean site.
Pairs of fish from the contaminated site performed more assessment displays compared to fish from clean sites. These results
suggest that the costs of living in an environment under exposure can shape behavioral repertoires. The altered conflict resolution
strategies of contaminated fish may reflect impaired cognitive function, sensory perception, and/or higher metabolic load
associated with aggression. This study provides support for the utilization of quantifiable behavioral differences as ecologically
relevant measures of contaminant exposure. 相似文献
16.
Tamara Fraizer 《Behavioral ecology and sociobiology》1997,41(6):423-434
I develop a state-based dynamic model of behavior to demonstrate that size-dependent differences in temperature tolerances
are not necessary to account for the activity of small male digger wasps late in the day. In the model, males defend or patrol
the nesting area, wait near nests, or feed away from the nesting area depending on time of day, energy reserves and size rank.
I assume a large male competitive advantage, so mating opportunities decrease with size rank for territorial or patrolling
males and are rare for all waiting males; the costs of patrolling or defense are higher than the costs of waiting. If energy
reserves of all males are initially small, all males alternate feeding and territorial or patrolling behavior. If energy reserves
are initially large, large males patrol or maintain territories until they risk starvation and leave the area to feed. At
this time, smaller males that have conserved their resources by waiting and feeding may defend territories or patrol. I simulate
the behavior of three populations representing two species of Microbembex by assuming large initial energy reserves for populations in which males were territorial and small initial reserves for
populations in which males patrolled, and then convert the predicted time of activity to temperature using local regressions
from field studies. Temporal patterns in the activity of large and small males were similar to those actually observed, and
relationships between size and temperature predicted by the model corresponded to most observations and were sometimes positive.
Thus, the delayed activity of smaller males does not correspond to activity at higher temperatures and is probably not attributable
to size-dependent thermal tolerances, but may represent a temporal displacement of mating activity due to intra-sexual competition
and mediated by energetics. The model makes testable predictions on the timing of feeding and depletion of energy reserves
in relation to size and initial energy state, and suggests how differences among species may influence the temporal and spatial
organization of male mating behavior.
Received: 27 February 1997 / Accepted after revision: 26 July 1997 相似文献
17.
Many species of territorial animals are more aggressive toward strangers than neighbors, a pattern of aggression referred
to as the ’dear-enemy phenomenon.’ In many cases, the mechanism by which neighbors are discriminated from strangers and the
function of neighbor-stranger discrimination remain controversial. We investigated the spatial patterns of inter-colony aggression
within and between two Pheidole species of seed-harvesting ants in the Mojave Desert of California by quantifying aggression between colonies in standardized
staged encounters. We also tested whether the level of fighting between workers of two colonies is affected by previous exposure
to each other. We show that neighbors (i.e., colonies less that 2.6 m away) of either species are treated less aggressively
than more distant colonies and that habituation may be a mechanism by which this discrimination is achieved. The variation
in aggression among spatially distant colonies also suggests that additional genetic or environmental factors are involved
in recognition. The function of the dear-enemy phenomenon in these ant species may be related to the greater risk to the resources
of a colony presented by strange workers than workers from a neighboring colony.
Received: 18 November 1999 / Received in revised form: 3 April 2000 / Accepted: 3 May 2000 相似文献
18.
Christian C. Voigt Otto von Helversen Robert Michener Thomas H. Kunz 《Behavioral ecology and sociobiology》2001,50(1):31-36
Saccopteryx bilineata has a polygynous mating system in which males defend females in a harem territory. Harem defense and courtship include energetically costly flight maneuvers and hovering displays. We tested if (1) harem males have a greater field metabolic rate than non-harem males or females and if (2) the field metabolic rate of harem males is correlated with the number of females in a harem territory. We measured the energy budget in 32 S. bilineata with the doubly labeled water method and compared these estimates with behavioral observations in the daytime roost. Among adult bats, field metabolic rate varied with body mass by an exponent of approximately two. We found no significant difference in field metabolic rate or mass-specific field metabolic rate between harem and non-harem males. The mass-specific field metabolic rate of harem-males increased with harem size. The latter finding supports the hypothesis that the energy costs of courtship display and territorial defense influence the energy budget of harem males. Overall, field metabolic rates of S. bilineata were lower than those of similarly sized bats of the temperate zone and only 2.3 times above the basal metabolic rate recorded for this species. We suggest that male S. bilineata did not take advantage of their metabolic capacity because a prudent allocation of energy to activities of harem maintenance is an adaptive strategy for males in this mating system. 相似文献
19.
Territoriality is of great significance for many species and a characteristic of most group-living animals. Territoriality is thought to lead to increased reproductive success by defending a particular area containing critical resources. I describe several factors that influence territorial aggression in free-ranging striped mice (Rhabdomys pumilio), a group-living solitary forager. I induced territorial aggression by attracting mice of different groups using bait either at territory boundaries or in front of nests. Striped mice are territorial and make decisions about whether or not to attack a mouse from another group based upon several factors: (1) the sex of the opponent: males are much more likely to attack strange males than strange females, whereas no sex specific aggression was observed in females; (2) the body size of the opponent: striped mice are much more likely to attack a strange mouse that is lighter than themselves; and (3) the location of encounters: striped mice are much more likely to attack strangers, even those significantly heavier than themselves, in front of the nest than at territory boundaries. These variations in territorial responses between different types of individuals may be due to the different ultimate consequences of territorial aggression for different animals.Communicated by S. Alberts 相似文献
20.
Abstract: The introduction of non‐native plant species and the release of genetically modified (GM) crops can induce environmental changes at gene to ecosystem levels. Regulatory frameworks such as the Convention on Biological Diversity or the EU Deliberate Release Directive aim to prevent environmental damage but do not define the term. Although ecologists and conservationists often refer to environmental effects of GM crops or invasive species as damage, most authors do not disclose their normative assumptions or explain why some environmental impacts are regarded as detrimental and others are not. Thus far, a concise definition of environmental damage is missing and is necessary for a transparent assessment of environmental effects or risks. Therefore, we suggest defining environmental damage as a significant adverse effect on a biotic or abiotic conservation resource (i.e., a biotic or abiotic natural resource that is protected by conservational or environmental legislation) that has an impact on the value of the conservation resource, the conservation resource as an ecosystem component, or the sustainable use of the conservation resource. This definition relies on three normative assumptions: only concrete effects on a conservation resource can be damages; only adverse effects that lead to a decrease in the value of the conservation resource can be damages; and only significant adverse effects constitute damage to a conservation resource. Applying this definition within the framework of environmental risk assessment requires further normative determinations, for example, selection of a threshold to distinguish between adverse and significant adverse effects and approaches for assessing the environmental value of conservation resources. Such determinations, however, are not part of the definition of environmental damage. Rather they are part of the definition's operationalization through assessment procedures, which must be grounded in a comprehensible definition of environmental damage. 相似文献