Agent‐based modeling of the effects of forest dynamics,selective logging,and fragment size on epiphyte communities

1. Forest canopies play a crucial role in structuring communities of vascular epiphytes by providing substrate for colonization, by locally varying microclimate, and by causing epiphyte mortality due to branch or tree fall. However, as field studies in the three‐dimensional habitat of epiphytes are generally challenging, our understanding of how forest structure and dynamics influence the structure and dynamics of epiphyte communities is scarce.
2. Mechanistic models can improve our understanding of epiphyte community dynamics. We present such a model that couples dispersal, growth, and mortality of individual epiphytes with substrate dynamics, obtained from a three‐dimensional functional–structural forest model, allowing the study of forest–epiphyte interactions. After validating the epiphyte model with independent field data, we performed several theoretical simulation experiments to assess how (a) differences in natural forest dynamics, (b) selective logging, and (c) forest fragmentation could influence the long‐term dynamics of epiphyte communities.
3. The proportion of arboreal substrate occupied by epiphytes (i.e., saturation level) was tightly linked with forest dynamics and increased with decreasing forest turnover rates. While species richness was, in general, negatively correlated with forest turnover rates, low species numbers in forests with very‐low‐turnover rates were due to competitive exclusion when epiphyte communities became saturated. Logging had a negative impact on epiphyte communities, potentially leading to a near‐complete extirpation of epiphytes when the simulated target diameters fell below a threshold. Fragment size had no effect on epiphyte abundance and saturation level but correlated positively with species numbers.
4. Synthesis: The presented model is a first step toward studying the dynamic forest–epiphyte interactions in an agent‐based modeling framework. Our study suggests forest dynamics as key factor in controlling epiphyte communities. Thus, both natural and human‐induced changes in forest dynamics, for example, increased mortality rates or the loss of large trees, pose challenges for epiphyte conservation.

     

The population metabolism and life history tactics of Neobisium muscorum (Leach) (Arachnida: Pseudoscorpiones)

Summary The population metabolism of N. muscorum at a beechwood site in southern England was determined for two separate year periods by two methods; a detailed computer analysis and a best estimate. These methods, which are based on data of biomass, population dynamics, field temperatures, and respiration rates of all life stages with temperature, are compared. The validity of extrapolating laboratory determined basal metabolic rates to field activity is discussed; and the population metabolism of N. muscorum is compared with that reported for other soil and litter invertebrate species, both predatory and non-predatory.The metabolic rates of the adults of a second species of pseudoscorpion found at the beechwood site (Chthonius orthodactylus (Leach)), were determined, and the life cycle and metabolism of this species is compared to N. muscorum. The influence of low environmental temperatures on poikilothermic predators, with reference to life cycle strategies, basal metabolism and geographic distribution, is discussed.     

Effects of salinity and temperature on oxygen consumption in a freshwater population of Palaemonetes antennarius (Crustacea,decapoda)

• 1.1. After step-like increases in salinity the shrimps exhibit the smallest increase in oxygen consumption in the lower salinity range. At higher salinities the shrimps show longer recovery times and greater increases in the metabolic rate after salinity shock.
• 2.2. In steady-state experiments, the shrimps display the lowest oxygen consumption rates near the isosmotic point. The lowest metabolic rates occur at salinities of 3‰ and 10‰ At salinities of 20‰ and above the rate of metabolism increases by 20–30%.
• 3.3. The calculated osmoregulatory work for animals in fresh water amounts to only 2.7% of routine metabolism and drops to 1.1% for shrimps in 3‰ and 0.7% in 5‰ salinity.
• 4.4. Locomotory activity in the form of position change was not responsible for the increased oxygen consumption of the animals after salinity shocks. A “tentative swimming activity” by fast and frequent beating of the pleopods without position change may be an important factor in the increase of metabolic rates.
• 5.5. In its temperature response, the brackish water population has a higher metabolic rate than the freshwater one. Between 5 and 35°C Q ₁₀-values range from 4.01 to 1.37.

     

The relationship between forage cell wall content and voluntary food intake in mammalian herbivores

• 1 It is generally assumed that animals compensate for a declining diet quality with increasing food intake. Differences in the response to decreasing forage quality in herbivores have been postulated particularly between cattle (ruminants) and horses (hindgut fermenters). However, empirical tests for both assumptions in herbivorous mammals are rare.
• 2 We collected data on voluntary food intake in mammals on forage‐only diets and related this to dietary neutral detergent fibre (NDF) content, assuming a nonlinear correlation between these measurements. Generally, the paucity of corresponding data is striking.
• 3 Elephants and pandas showed very high food intakes that appeared unrelated to dietary fibre content. Only in small rodents, and possibly in rabbits, was an increase in food intake on forages of higher NDF content evident. In particular, other large herbivores, including horses, followed patterns of decreasing intake with increasing forage NDF, also observed in domestic cattle or sheep.
• 4 For large herbivores, empirical data therefore do not – so far – support the notion that intake is increased in response to declining diet quality. However, data are in accord with the assumption that most large herbivores have an anticipatory strategy of acquiring body reserves when high‐quality forage is available, and reducing food intake (and potentially metabolic losses) when only low‐quality forage is available.
• 5 Intake studies in which the influence of digestive strategy on food intake capacity is tested should be designed as long‐term studies that outlast an anticipatory strategy and force animals to ingest as much as possible.
• 6 We suggest that a colonic separation mechanism coupled with coprophagy, in order to minimize metabolic faecal losses, is necessary below a body size threshold where an anticipatory strategy (living off body reserves, migration) is not feasible. Future studies aimed at investigating fine‐scale differences, for example between equids and bovids, should focus on non‐domesticated species.

     

始红蝽呼吸代谢的季节变化及对温度的适应性

为阐明始红蝽呼吸代谢的季节变化规律,探讨其对温度适应的呼吸代谢策略,运用多通道昆虫呼吸仪逐月测定始红蝽自然种群的O_2吸收率、CO_2释放率、代谢率和呼吸商。基于预实验获得始红蝽完成一次完整的呼吸代谢活动的时间为90 s,故每90 s记录1次数据。结果表明,始红蝽的呼吸代谢存在明显的季节变化。冬季种群(12—2月)呼吸代谢水平最弱,O_2吸收率、CO_2释放率和代谢率的平均值依次为(3.16±1.02)×10~(-5)mL/min、(2.09±0.78)×10~(-5)m L/min、(0.11±0.08)×10-3mLg~(-1)min~(-1);春季种群(3—5月)呼吸代谢水平迅速增加,夏季种群(6—8月)呼吸代谢水平最高,O_2吸收率、CO_2释放率和代谢率的平均值分别为(33.68±2.68)×10~(-5)mL/min、(36.00±3.07)×10~(-5)m L/min、(18.16±0.83)×10-3m Lg~(-1)min~(-1);秋季种群的呼吸代谢水平开始减弱并持续到冬季。始红蝽O_2吸收率、CO_2释放率和代谢率的值与栖息地的地表温度成正相关(r_1=0.914,r_2=0.909,r_3=0.836);春、夏、秋3个季节始红蝽以糖类物质作为呼吸代谢消耗的底物,冬季则消耗脂类物质。研究得出,随季节温度变化,始红蝽不仅能够调节呼吸代谢水平的强弱以提高自身对温度的适应能力,还可通过调整呼吸代谢消耗的底物类型以最大程度降低消耗,这对维持始红蝽种群数量和扩大其地理分布具有重要的生态学意义。     

Shade tolerance and herbivory are associated with RGR of tree species via different functional traits

• Relative growth rate (RGR) plays an important role in plant adaptation to the light environment through the growth potential/survival trade‐off. RGR is a complex trait with physiological and biomass allocation components. It has been argued that herbivory may influence the evolution of plant strategies to cope with the light environment, but little is known about the relation between susceptibility to herbivores and growth‐related functional traits.
• Here, we examined in 11 evergreen tree species from a temperate rainforest the association between growth‐related functional traits and (i) species’ shade‐tolerance, and (ii) herbivory rate in the field. We aimed at elucidating the differential linkage of shade and herbivory with RGR via growth‐related functional traits.
• We found that RGR was associated negatively with shade‐tolerance and positively with herbivory rate. However, herbivory rate and shade‐tolerance were not significantly related. RGR was determined mainly by photosynthetic rate (A_max) and specific leaf area (SLA). Results suggest that shade tolerance and herbivore resistance do not covary with the same functional traits. Whereas shade‐tolerance was strongly related to A_max and to a lesser extent to leaf mass ratio (LMR) and dark respiration (R_d), herbivory rate was closely related to allocation traits (SLA and LMR) and slightly associated with protein content.
• The effects of low light on RGR would be mediated by A_max, while the effects of herbivory on RGR would be mediated by SLA. Our findings suggest that shade and herbivores may differentially contribute to shape RGR of tree species through their effects on different resource‐uptake functional traits.

     

Low temperature mortality of the peach-potato aphid Myzus persicae

ABSTRACT.

• 1 The mean supercooling points of first instar and adult Myzus persicae (Sulzer) maintained at 20°C and cooled at 1°C min^?1 were ?26.6 and ?25.0°C respectively.
• 2 The LT₅₀ (temperature) of the same age groups drawn from the same population and cooled at the same rate were ?8.1 and ?6.9°C, indicating extensive pre-freeze mortality in M.persicae under laboratory conditions.
• 3 Acclimation at 10 and 5°C did not affect supercooling but depressed the LT₅₀ of both first instars and adult aphids.
• 4 Freezing of leaves during feeding did not increase mortality above that expected from the direct effects of low temperature.
• 5 The level of cold in different winters can be expressed in terms of the total number of frost days, and the frequency of abnormally cold days. Winter temperatures differ markedly in a vertical profile from the soil to the soil or grass surface, and then to the air (and foliage) above.
• 6 The time of the first record of M.persicae in suction trap samples is correlated with January and February temperatures except in the west of England and Wales. Further north December and January temperatures are relatively more important.
• 7 Winter temperatures and the resultant aphid mortality is a primary determinant of the timing of the spring migration.

     

Potential rates of Increase of solitarious and gregarious phases of the African armyworm Spodoptera exempta (Lepidoptera: Noctuidae)

Abstract.

• 1 The African armyworm Spodoptera exempta exhibits a phase polyphenism with insects capable of transforming from one‘phase’to another, which involves both physiological and behavioural changes. Amongst these changes, evidence from the laboratory and the field suggest that, given equivalent conditions of temperature and food, solitary phase insects take longer to complete their life cycles than gregarious phase insects, and the latter's generations are more synchronized. There is also some evidence that females of the solitary form sometimes lay more eggs.
• 2 Using data from field and laboratory studies, estimates of the rates of increase of each form were calculated from Leslie matrix models. Assuming equivalent mortality rates for both phases, asynchronous development for the solitaries and synchronous development for the gregarious forms, with the latter having lower fecundities than the solitaries, the models suggest that the gregarious forms have higher values of their intrinsic rates of increase (r) than solitarious populations. These results are explored using a range of parameter values including variation in the percentage of solitaries with delayed development.
• 3 The possible ecological and evolutionary significance of variations in rates of increase of gregarious and solitary populations are briefly discussed.

     

Phenology and flight periodicity of Sirex noctilio (Hymenoptera: Siricidae) in central New York,U.S.A.

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The roles of energetics,water economy,foraging behavior,and geothermal refugia in the distribution of the bat,Macrotus californicus

Summary Energy metabolism, thermoregulation, and water flux ofMacrotus californicus, the most northerly representative of the Phyllostomidae, were studied in the laboratory using standard methods, and energy metabolism and water fluxes were studied in the field using the doubly labelled water method together with a time budget. Daily energy expenditures of free-living bats averaged 22.8 kJ during the winter study period. Approximately 60% of this was allocated to resting metabolism costs while in the primary roosts (22 h/day).Macrotus californicus is unable to use torpor. The thermoneutral zone (TNZ) in this species is narrow (33 to 40 °C) and metabolic rate increased rapidly as ambient temperature decreased below the TNZ. Basal metabolic rate was 1.25 ml O₂/g·h, or 24 J/g·h. Total thermal conductance below the TNZ. was 1.8 mW/g·°C, similar to values measured for other bats. Evaporative water loss showed a hyperbolic increase with increasing ambient temperature, and was approximately 1% of total body mass/h in the TNZ. The success of these bats as year-round residents in deserts in the southwestern United States is probably not due to special physiological adaptations, but to roosting and foraging behavior. They use geothermally-heated winter roost sites (stable year-round temperatures of approximately 29 °C) which minimize energy expenditures, and they have an energetically frugal pattern of foraging that relies on visual prey location. These seem to be the two major factors which have allowedM. californicus to invade the temperate zone.Abbreviations BMR basal metabolic rate - FMR field metabolic rate - T _a ambient temperature - T _b body temperature - T _lc,T _uc lower and upper critical temperature, respectively - TBW total body water - TNZ thermoneutral zone     

The roles of top and intermediate predators in herbivore suppression: contrasting results from the field and laboratory

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Life cycle and food availability indices in Notiophilus biguttatus (Coleoptera, Carabidae)

Abstract.

• 1 Food demands of the predatory carabid Notiophilus biguttatus F. and their fulfilment were studied in the laboratory and field.
• 2 In the laboratory, larval consumption, growth, adult body size and egg production were established for different regimes of temperature and food, the springtail Orchesella cincta.
• 3 Temperature strongly influenced feeding rate of larvae and adults and consequently growth and oviposition rates. Accordingly, growth rate and ovi-position rate increased with prey supply.
• 4 Prey supply also had an effect on fat content, but the number of ripe eggs in the ovaries was related neither to temperature nor to prey supply.
• 5 Adult body size was affected by temperature during the larval period but more so by food supply.
• 6 Dissection of field fresh females showed them to bear eggs for the whole year, except in late winter/early spring and in July.
• 7 Fat content was low in spring and, from July on, high in summer and autumn. Survivorship during starvation differed widely between samples and seemed to be related to reproductive status rather than to fat content.
• 8 Samples of beetles and springtails from eleven pine plantations revealed for the beetles significant differences in fat content and body size, the latter ranging between the maximum and minimum value obtained in the laboratory.
• 9 Conclusions about food limitation based on body size and fat content were not corroborated by a relationship of these indices with springtail density.

     

Factors affecting oxygen consumption in wild-caught yellow-bellied marmots (Marmota flaviventris)

• 1.1. All age groups gained mass during the active season, but mass-gain of adult females was delayed during lactation.
• 2.2. The relationship of body mass to metabolic rate varied widely; when the relationship was significant, R² varied from 10.3 to 72.6%. Body mass affects V_O2 more during lactation than at any other period.
• 3.3. Mean VinO₂ of adult males was higher in June than that of adult, non-lactating females.
• 4.4. V_O2 of reproductive females was significantly higher during lactation than during gestation or postlactation because specific V_O2 varied. Specific V_O2 of non-reproductive females declined over the active season.
• 5.5. Specific V_O2 of all age groups declined between the premolt and postmolt periods. The reduced maintenance costs can contribute 20–46% to daily growth.
• 6.6. Observed V_O2 was lower than the value predicted from intraspecific or interspecific Bm:M regressions.
• 7.7. V_O2 of wild-caught marmots was lower than that of marmots maintained in the laboratory, probably because of dietary differences.
• 8.8. Because basal metabolism is a stage on a food-deprivation curve, we suggest that basal metabolic rate is not an appropriate measure of the metabolic activity of free-ranging animals.

     

Fluctuating water levels control water chemistry and metabolism of a charophyte‐dominated pond

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Vascular epiphyte populations with higher leaf nutrient concentrations showed weaker resilience to an extreme drought in a montane cloud forest

• Leaf stoichiometry can characterize plant ecological strategies and correlate with plant responses to climate change. The role of vascular epiphytes in the ecosystem processes of tropical and subtropical forest ecosystems cannot be ignored. Vascular epiphytes are very vulnerable to climate change, however, the relationship between the response of epiphytes to climate change and leaf stoichiometry is not well understood.
• We present data for 19 vascular epiphyte species that were collected during four consecutive censuses (in 2005, 2010, 2015, and 2020) over 15 years in a subtropical montane cloud forest. We assessed the relationships between the population dynamics and leaf stoichiometry of these vascular epiphytes.
• Experiencing an extreme drought, 14 of the 19 epiphyte species showed an obvious decrease in the number of individuals, and all species showed negative growth in the number of populations. Subsequently, the total number of individuals gradually recovered, increasing from 7,195 in 2010 to 10,121 in 2015, then to 13,667 in 2020. The increase in the number of vascular epiphyte individuals from 2010 to 2015 was significantly negatively correlated with leaf nitrogen and phosphorus concentration, and was significantly positively correlated with the leaf carbon-nitrogen ratio.
• Vascular epiphyte populations with higher leaf nutrient concentrations exhibited weaker resilience to the extreme drought, which demonstrated that a resource-conservative strategy was advantageous for the recovery of epiphyte populations. Our findings suggest that ecological stoichiometry can be a useful framework for forecasting the dynamics of vascular epiphyte populations in response to climate change.

     

三江平原农田土壤跳虫多尺度空间自相关性

土壤动物多尺度空间自相关性特征是土壤动物空间异质性和空间共存格局研究的重要基础。以土壤跳虫为研究对象,以中国科学院三江平原沼泽湿地生态实验站为研究区,于2011年8月和10月,选取具30 a以上耕作历史的旱地为实验样地,以5 m为步长设置一个50 m×50 m的实验样地,采用地统计中的全局Moran's I指数和局部Moran's I指数相结合的方法,研究土壤跳虫多尺度空间自相关性特征。全局空间自相关结果表明,土壤跳虫群落总密度和多数跳虫种类存在显著的多尺度空间自相关特征,多数为显著的正的空间自相关性,形成明显的空间集群。局部空间自相关结果表明,土壤跳虫群落总密度和所有跳虫种类均存在显著的局部空间自相关性,在局部地区形成"高—高"和/或"低—低"的空间集群,并和"高—低"和/或"低—高"的空间孤立区相伴发生,即形成"斑块"和"孔隙"相间分布的水平镶嵌格局;这种镶嵌格局具一定的时间动态特征,从夏季到秋季斑块大小和空间分布范围略有变化。研究表明,土壤跳虫具有明显的多尺度空间自相关性;空间集群是土壤跳虫的常见空间分布格局,在样地内形成"斑块"和"孔隙"相间分布的水平镶嵌格局,这种格局具年内时间变异性。     

Sowing of margin strips rich in floral resources improves herbivore control in adjacent crop fields

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METABOLISM OF AMINO ACIDS IN INCUBATED SLICES OF MOUSE BRAIN1

• 1 Slices of mouse brain were incubated with [U-¹⁴C]alanine, valine, leucine, phenylalanine, proline, histidine, lysine, arginine or aspartic acid, and the extent of metabolism was estimated by analyses utilizing paper chromatography of the tissue extracts and with an amino acid analyser.

• 2 The metabolism of Ala and Asp was high; of Leu and Pro, moderate; and of Lys, Arg and Phe, low; the metabolism of Val and His was not significant. The time-course of metabolism in most cases showed varying rates, indicating heterogeneous metabolic compartments for the amino acids.

• 3 Production of CO₂ was high from Asp, moderate from Ala, and low from Leu; the other amino acids were not oxidized to CO₂ to any significant extent. A large portion of the metabolized label was trapped in the form of Glu or Asp.

• 4 Metabolism increased with increasing concentration of amino acid to some extent and was largely inhibited by omission of glucose, by anaerobic conditions, or by cyanide. Although these conditions also inhibit uptake, the time-course and extent of inhibition uptake and metabolism were different.

• 5 With Asp, Ala and Phe, metabolism was lowest in slices from pons-medulla; the brain area exhibiting the highest metabolism differed for each amino acid. The metabolism of Asp was lower in brain samples from newborn than in those from adults; the metabolism of Leu was higher in slices from newborn brain.

• 6 The results indicate that the majority of the amino acids can be metabolized in brain tissue and that the metabolic rates are influenced by a number of factors, among them the level of amino acids and the level of available energy.

     

Coexistence of two species of Binella Motchulsky (Coleoptera: Ptiliidae) and the significance of their adaptation to different temperature ranges

Abstract.

• 1 Ptinella aptera and Ptinella errabunda often coexist where their distributions overlap.
• 2 The ecological requirements of P.aptera and P.errabunda are similar. Both are generalized mycetophages restricted to the same subcortical habitat of trees in a particular state of decay. Relative humidity appears important in determining habitat suitability for both species, neither of which survived in laboratory regimes below approximately 100% relative humidity.
• 3 In laboratory studies the beetles differed in their response to temperature. Recorded maxima for activity and rate of increase were at higher temperatures for P.aptera than for Perrabunda.
• 4 Temperatures which ‘Ptinella were exposed to in the laboratory occur in natural conditions under bark. Their effects on the species’ distributions are considered.
• 5 The differential temperature adaptations of P.aptera and P.errabunda were probably evolved in allopatry, in response to different environmental conditions. In view of this, it is unreasonable to infer past interspecies competition from these niche differences.
• 6 The niche difference between coexisting Ptinella species is discussed in the light of current ideas concerning the relative importance of competition and other factors in natural communities.

     

The arthropod predators of ant-mimetic and aposematic prey: a serological analysis

Abstract.

• 1 ELISA (enzyme-linked immunosorbant assay) was used to identify the arthropod predators of two common herbivores of a desert lupine: the aposematic plant bug Lopidea nigridea and the ant-mimetic plant bug Coquillettia insignis.
• 2 Despite the fact that the prey are closely related, the two antisera were sufficiently specific to distinguish between the antigen against which they were formed and the antigen of the other species: both antisera were 3 times as reactive against their homologous antigen as they were against their heterologous antigen.
• 3 In tests on gut contents of field-collected predators, ELISA results were generally consistent with laboratory no-choice data for the five most common arthropod species on lupine: there was a strong correlation between attack rates for each predator-prey pair as measured in the laboratory, and per cent positive reactions in ELISA as measured using field-collected predators. In particular, L.nigridea antiserum was shown to be significantly less reactive against the crab spider Xysticus montanensis when compared to C.insignis antiserum, paralleling results of laboratory no-choice experiments.
• 4 The usefulness of serological analysis as a tool for arthropod trophic link identification is discussed.