Evidence supporting the importance of terrestrial carbon in a large-river food web

Algal carbon has been increasingly recognized as the primary carbon source supporting large-river food webs; however, many of the studies that support this contention have focused on lotic main channels during low-flow periods. The flow variability and habitat-heterogeneity characteristic of these systems has the potential to significantly influence food web structure and must be integrated into models of large-river webs. We used stable-isotope analysis and IsoSource software to model terrestrial and algal sources of organic carbon supporting consumer taxa in the main channel and oxbow lakes of the Brazos River, Texas, USA, during a period of frequent hydrologic connectivity between these habitat types. Standardized sampling was conducted monthly to collect production sources and consumer species used in isotopic analysis. Predictability of hydrologic connections between habitat types was based on the previous 30 years of flow data. IsoSource mixing models identified terrestrial C3 macrophytes (riparian origin) as the primary carbon source supporting virtually all consumers in the main channel and most consumers in oxbow lakes. Small-bodied consumers (<100 mm) in oxbow lakes assimilated large fractions of algal carbon whereas this pattern was not apparent in the main channel. Estimates of detritivore trophic positions based on delta15N values indicated that terrestrial material was likely assimilated via invertebrates rather than directly from detritus. High flows in the river channel influenced algal standing stock, and differences in the importance of terrestrial and algal production sources among consumers in channel vs. oxbow habitats were associated with patterns of flooding. The importance of terrestrial material contradicts the findings of recent studies of large-river food webs that have emphasized the importance of algal carbon and indicates that there can be significant spatial, temporal, and taxonomic variation in carbon sources supporting consumers in large rivers.     

Stable isotope and biochemical fractionation in the marine pelagic food chain: the jellyfish Pelagia noctiluca and net zooplankton

In our field study we analyzed the C and H isotopic and biochemical (C, N, P, protein, lipid, carbohydrate) composition of the jellyfish Pelagia noctiluca (collected from the Gulf of Trieste in 1985 to 1986) and its presumed diet-net zooplankton. The mean ¹³C (-18.8) and D (-58.4) ratios of P. noctiluca showed enrichment in heavy isotopes relative to net zooplankton (2 for carbon and 30 for hydrogen). Both the jellyfish and net zooplankton were characterized by a linear correlation between ¹³C and D. C. N, P, protein, lipid, and carbohydrate contents of P. noctiluca were low on a dry weight basis as compared to net zooplankton. Significantly lower C:N and C:P ratios were found in jellyfish indicating a greater loss of carbon relative to nitrogen and phosphorus along the passage to a higher trophic level. Isotopic and biochemical evidence indicate that, though collected in nearshore waters, P. noctiluca depended on autochthonous marine organic matter.     

Photosynthetic responses and daily carbon balance ofColpomenia peregrina: Seasonal variations and differences between intertidal and subtidal populations

The seasonal photosynthetic responses and daily carbon gain of upper intertidal, low intertidal and subtidal (3 to 4 m depth) populations ofColpomenia peregrina were examined over a 2 yr period (1986–1988) in Santa Catalina Island, California, USA. The populations showed significant differences in their photosynthetic responses, daily carbon balance and carbon-specific growth rates when normalized to tissue area or to chlorophyll content. The substantial plasticity with respect to photosynthetic responses shown byC. peregrina is considered to be an important factor in facilitating the colonization of both intertidal and subtidal habitats. This species appears to have a cellular carbon metabolism influenced by responses to season and tidal elevation. Highest net daily carbon balance, predicted carbonspecific growth rates and net growth efficiency were achieved in upper intertidal habitats during summer. These parameters decreased in winter and progressively declined with increasing depth as plants become increasingly exposed to low-light regimes. The diminishing net daily carbon balance and predicted carbon-specific field growth rates found during winter suggest that standing stock and lower subtidal limits of distribution ofC. peregrina are at least partly controlled by these two factors.     

Size fractionation of natural aquatic populations associated with autotrophic and heterotrophic carbon uptake

Natural phytoplankton samples from the Gulf of California were incubated with radioactive bicarbonate or glucose, with or without the addition of gentamycin, a broad spectrum antibiotic which inhibits bacterial activity but has little effect on many algae. The relative distribution of chlorophyll and radioactivity in particles retained by filters of 3 and 0.45 μ mean pore size was measured. From 13 to 83% of the ¹⁴C-bicarbonate assimilated by natural populations appeared to be associated with organisms having a smallest dimension less than 3 μ. These were probably algae, since the distribution of chlorophyll on the filters was similar to that of the radioactivity. Furthermore, gentamycin treatment did not change the distribution of radioactivity from ¹⁴C-bicarbonate. In these waters, considerable photosynthesis may be carried out by ultra-nannoplankton (3 to 1 μ). Glucose was assimilated mainly by bacteria, of which more than 90% passed through 3 μ filters. Gentamycin significantly reduced glucose uptake in most cases. Although this method cannot be adopted uncritically for the estimation of carbon flux from photoautotrophs to heterotrophs, differential filtration can be used to elucidate the size distribution of various metabolic groups in the plankton.     

气候变化背景下中国陆地生态系统碳储量及碳通量研究进展

全球气候变化对全球生态系统的结构、功能和过程产生了重要影响,成为各国政府、社会公众以及科学界共同关心的焦点问题。陆地生态系统碳循环又是当前气候变化和区域可持续发展研究的核心内容之一,影响到经济和社会发展的各个方面。因此,开展陆地生态系统碳储量和碳通量的研究仍将是气候变化研究中的重点内容。总结了近年来国内森林、土壤、草地、农田四种陆地生态系统在碳储量、碳通量方面取得的研究成果和不足：随着遥感、GIS及模型的发展和应用,森林、草地生态系统碳储量的研究精度和范围要高于农田和土壤,而农田和土壤生态系统碳储量的研究多基于典型性样地和大量实验数据,结果受制于样点布设和采样密度;目前,土壤生态系统碳储量结果多基于上世纪80年代全国二次土壤普查数据计算所得,且总有机碳库的估算存在较大差异,土壤有机碳的组分研究中易氧化有机碳库研究滞后于总有机碳,迫切需要对我国现有土壤有机碳进行研究;农田生态系统受人类活动干扰强烈,从一个或几个站点到全国尺度都有对农田土壤有机碳贮量的研究成果,与国外相比,我国试验田的设置时间短,资料积累较少,更多侧重不同施肥方式下农作物产量和农田合理的施肥培肥模式研究,农田土壤有机碳含量关系我国农业生产和粮食安全,对农田土壤固碳机理的研究仍将是今后关注的焦点。各生态系统碳通量的监测取得了一定成果,近年来涡度相关系统在森林、土壤、草地、农田生态系统中得到了广泛的应用。并从气候、人类活动两个因素分析了其对生态系统碳储量、碳通量的影响。针对目前存在的问题,进一步指出了目前国内不同生态系统中碳循环在现状研究、有机碳变化机制、模型建立及气候变化和人类活动影响下的碳库时空格局方面得到加强。     

Stable carbon isotope variability in marine macrophytes and its implications for food web studies

Stable carbon isotope ratios (¹³C) of eelgrass Zostera marina and of kelp Laminaria longicruris showed considerable variation in time and space. The isotopic composition of Z. marina varied seasonally from a mean of-6 for leaves formed in June to a mean of-10 for leaves formed in February. The maximum range for individual leaves was from-5 to-11.4. Once a leaf was fully formed, its isotopic composition appeared not to change. In L. longicruris there was no clear seasonal pattern of variation, but in any given blade there was a spatial pattern of variation, with the thickened central band tending to be least negative and the margins most negative. In one blade the range was from-12 to-20. Since this range overlaps values that are found in various other macrophytes and in seston, the value of the stable carbon isotope ratio as a tracer in food webs involving macroalgae is questioned. For Z. marina, in which the values are seasonally predictable, the technique may be useful if interpreted with care. The most probable explanation of variation in the ratios is differential storage of biochemical components of different isotopic compostion.     

Reciprocal subsidies between freshwater and terrestrial ecosystems structure consumer resource dynamics

Cross-ecosystem movements of material and energy, particularly reciprocal resource fluxes across the freshwater-land interface, have received major attention. Freshwater ecosystems may receive higher amounts of subsidies (i.e., resources produced outside the focal ecosystem) than terrestrial ecosystems, potentially leading to increased secondary production in freshwaters. Here we used a meta-analytic approach to quantify the magnitude and direction of subsidy inputs across the freshwater-land interface and to determine subsequent responses in recipient animals. Terrestrial and freshwater ecosystems differed in the magnitude of subsidies they received, with aquatic ecosystems generally receiving higher subsidies than terrestrial ecosystems. Surprisingly, and despite the large discrepancy in magnitude, the contribution of these subsidies to animal carbon inferred from stable isotope composition did not differ between freshwater and terrestrial ecosystems, likely due to the differences in subsidy quality. The contribution of allochthonous subsidies was highest to primary consumers and predators, suggesting that bottom-up and top-down effects may be affected considerably by the input of allochthonous resources. Future work on subsidies will profit from a food web dynamic approach including indirect trophic interactions and propagating effects.     

Priming effect: bridging the gap between terrestrial and aquatic ecology

Understanding how ecosystems store or release carbon is one of ecology's greatest challenges in the 21st century. Organic matter covers a large range of chemical structures and qualities, and it is classically represented by pools of different recalcitrance to degradation. The interaction effects of these pools on carbon cycling are still poorly understood and are most often ignored in global-change models. Soil scientists have shown that inputs of labile organic matter frequently tend to increase, and often double, the mineralization of the more recalcitrant organic matter. The recent revival of interest for this phenomenon, named the priming effect, did not cross the frontiers of the disciplines. In particular, the priming effect phenomenon has been almost totally ignored by the scientific communities studying marine and continental aquatic ecosystems. Here we gather several arguments, experimental results, and field observations that strongly support the hypothesis that the priming effect is a general phenomenon that occurs in various terrestrial, freshwater, and marine ecosystems. For example, the increase in recalcitrant organic matter mineralization rate in the presence of labile organic matter ranged from 10% to 500% in six studies on organic matter degradation in aquatid ecosystems. Consequently, the recalcitrant organic matter mineralization rate may largely depend on labile organic matter availability, influencing the CO2 emissions of both aquatic and terrestrial ecosystems. We suggest that (1) recalcitrant organic matter may largely contribute to the CO2 emissions of aquatic ecosystems through the priming effect, and (2) priming effect intensity may be modified by global changes, interacting with eutrophication processes and atmospheric CO2 increases. Finally, we argue that the priming effect acts substantially in the carbon and nutrient cycles in all ecosystems. We outline exciting avenues for research, which could provide new insights on the responses of ecosystems to anthropogenic perturbations and their feedbacks to climatic changes.     

Interspecific differences in the photosynthetic carbon metabolism of marine phytoplankton

Six species of marine phytoplankton of different sizes and taxonomic categories were grown in microcosms under identical experimental conditions; the species cultured were: Pavlova lutheri (Prymnesiophyceae), Dunaliella tertiolecta (Chlorophyceae), Phaeodactylum tricornutum (Baciollariophyceae), Eutreptiella sp. (Euglenophyceae), Alexandrium tamarense (Dinophyceae), and Phaeocystis pouchetii (Prymnesiophyceae). The photosynthetic carbon metabolism of these phytoplankton was studied throughout the exponential and lag phases of growth after nutrient depletion. The relative incorporation of carbon into protein was positively correlated with phytoplankton growth, while carbon assimilation into low molecular weight metabolites (LMWM) and storage products, i.e., lipid and polysaccharides, generally increased under nutrient-limiting conditions. Clear taxonspecific differences were observed in the proportions of carbon incorporated into cell constituents. A significant linear relationship was consistently found between the relative synthesis of protein to LMWM, and both the production normalised to chlorophyll (P:B) and the phytoplankton growth rate. However, ANCOVA revealed significant, interspecific differences in these relationships.     

陆地碳平衡对大气CO_2升高的响应及其机制

研究陆地碳平衡对大气CO2浓度升高的响应,能为揭示碳失汇之迷提供有力证据,为制定缓解全球变化的合理政策措施提供理论依据.综述了陆地碳平衡对全球大气CO2升高的响应及其町能的机制,由于陆地生态系统的复杂性,以及不同的研究在具体的对象、时间、地点、方法和角度的差异,目前有关陆地碳平衡对全球大气CO2升高的响应还存在很大的分歧.陆地碳库主要可分为植被碳库和土壤碳库,大气CO2浓度升高主要是通过影响光合作用、土壤养分、水分供应、光照条件、群落组成、光合产物分配等方式影响植被碳库;而土壤碳库的响应机理主要包括光合产物向土壤的输入量、脱落物质量、养分循环、光合产物分配、根系周转期、微生物活性等的响应.关于陆地碳平衡对全球大气CO2升高的响应今后应该主要集中在:(1)不同生态系统影响全球植被碳库变化的主导因子;(2)大气CO2浓度升高与其他环境因子的互作效应;(3)大气CO2浓度升高对植物光合作用的促进效应与光合作用适应性间的关系;(4)地上碳库与地下碳库间的相关性,及其对大气CO2浓度升高的分别响应;(5)克服目前实验方法存在的局限性.     

Diet and trophic position of Atlantic bluefin tuna (<Emphasis Type="Italic">Thunnus thynnus</Emphasis>) inferred from stable carbon and nitrogen isotope analysis

Stable ¹³C and ¹⁵N isotope analyses of scale, bone, and muscle tissues were used to investigate diet and trophic position of North Atlantic bluefin tuna (Thunnus thynnus Linnaeus) during residency in the northwest Atlantic Ocean off the northeast coast of the United States. Adult bluefin tuna scales collected from fish between June and October 2001 were significantly enriched in ¹³C compared to both muscle and bone across all months, while muscle was significantly enriched in ¹⁵N compared to either bone or scale throughout the same period. In muscle tissue, there was evidence of a shift over the summer from prey with ¹³C values (–17 to –18) that were characteristic of silver hake (Merluccius bilinearis) to species with ¹³C values of –20 to –21 that were similar to Atlantic herring (Clupea harengus) and sandlance (Ammodytes americanus). Depletion of ¹⁵N values in adult scales and bone compared to muscle tissue may be explained by bone and scale samples representing juvenile or life-long feeding habits, isotopic routing, or isotopic differences in amino acid composition of the three tissue types. Adult bluefin tuna were estimated to be feeding at a trophic position similar to pelagic sharks in the northwest Atlantic Ocean, while the trophic positions of yellowfin tuna (Thunnus albacares), albacore tuna (Thunnus alalunga), and juvenile bluefin tuna were indicative of a diet of up to a full trophic position below adult bluefin tuna. The close relationship between the juvenile bluefin ¹⁵N values and those of suspension feeders suggests that nektonic crustaceans or zooplankton may contribute significantly to the diet of bluefin tuna, a food source previously overlooked for this species in the northwest Atlantic Ocean.Communicated by J.P. Grassle, New Brunswick     

Effect of nitrogen deposition on China's terrestrial carbon uptake in the context of multifactor environmental changes

The amount of atmospheric nitrogen (N) deposited on the land surface has increased globally and by nearly five times in China from 1901 to 2005. Little is known about how elevated reactive N input has affected the carbon (C) sequestration capability of China's terrestrial ecosystems, largely due to the lack of reliable data on N deposition. Here we have used a newly developed data set of historical N deposition at a spatial resolution of 10 km x 10 km in combination with other gridded historical information on climate, atmospheric composition, land use, and land management practices to drive a process-based ecosystem model, the dynamic land ecosystem model (DLEM) for examining how increasing N deposition and its interactions with other environmental changes have affected C fluxes and storage in China's terrestrial ecosystems during 1901-2005. Our model simulations indicate that increased N deposition has resulted in a net C sink of 62 Tg C/yr (1 Tg = 1012 g) in China's terrestrial ecosystems, totaling up to 6.51 Pg C (1 Pg = 10(15) g) in the past 105 years. During the study period, the N-induced C sequestration can compensate for more than 25% of fossil-fuel CO2 emission from China. The largest C sink was found in southeast China, a region that experienced the most significant increase of N deposition in the period 1901-2005. However, the net primary productivity induced by per-unit N deposition (referred to as ecosystem N use efficiency, ENUE, in this paper) has leveled off or declined since the 1980s. This indicates that part of the deposited N may not be invested to stimulate plant growth, but instead leave the ecosystem by various pathways. Except shrubland and northwest/southwest China, signs of N saturation are apparent in the rest major biome types and regions, with ENUE peaking in the 1980s and leveling off or declining thereafter. Therefore, to minimize the excessive N pollution while keeping the N-stimulated C uptake in China's terrestrial ecosystems, optimized management practices should be taken to increase N use efficiency rather than to keep raising N input level in the near future.     

Modelling the potential impacts of land use/cover change on terrestrial carbon stocks in north-west Morocco

Terrestrial ecosystems store more carbon (C) than the atmosphere and provide ecosystem services (ES) such as global climate regulation, by sequestering carbon within biomass and soil. Land use land cover (LULC) change is considered a key factor, playing an important role in the dynamic variations of carbon storage. The aim of this paper is to assess the effects that LULC has had on carbon stocks and consequently on climate change regulation in north-western Morocco over 21 years. To achieve this aim, the Integrated Valuation of ES and Trade-offs (InVEST) model is used to assess status and variation in the net amount of carbon stored by the different types of LULC, and the economic value of the carbon sequestered in the remaining stock. The results show that the total carbon stock increased from 4.81TgC in 1996 to 4.98TgC in 2017. Over the 21 years, the LULC changes had the greatest effect on carbon storage - an increase of 6.87% with 0.17TgC of carbon sequestered, since the majority of unused land was changed to forest and cultivated land. Based on the global costs of atmospheric carbon, we estimate the economic value of carbon storage services to be between US$1,800,000 and US$3,570,000 for the whole period, with an average yearly increment of between US$86,000 and US$170,000. The results show that the ecosystem management has had a substantial climate mitigation effect. Also, the possibility of paying for ES could inform policy on the adoption of LULC to support livelihood and management choices.     

Relationships between carbon and cadmium uptake in Mytilus edulis

The influence of six different food rations on carbon assimilation and net incorporation, and on shell and soft body growth in Mytilus edulis was determined over a 75-d period, starting in 1981. Using a triple tracer technique, interrelationships between carbon net incorporation (C-14) and cadmium accumulation from food (Cd-109) and seawater (Cd-115m) were investigated. With decreasing food rations there was an exponential increase of the carbon assimilation efficiency from 35 to 76% while the net incorporation efficiency increased approximately linearly, ranging from 15 to 32% at the highest and lowest food supply levels respectively. The carbon assimilation efficiency adapted to new conditions within 1 to 2 d while the adaptation of the net incorporation efficiency took about one month. Shells kept growing, even when the soft body lost weight. Within a 42-d elimination period, when the soft body lost 58% of the incorporated carbon, nothing was released from the shells. Cadmium accumulation from food was closely interrelated with carbon net incorporation and exhibited the same uptake kinetics. No homogeneity was found between carbon net incorporation and cadmium accumulation from seawater, and between the elimination of carbon and cadmium.     

毛白杨杂种无性系稳定碳同位素值的特征及其水分利用效率

2008年在北京林业大学对9个毛白杨(Populus tomentosa)杂种无性系苗木生长不同时期的叶片、小枝、根的碳同位素δ~(13)C和瞬时水分利用效率WUEi的差异进行研究,分析不同无性系间δ~(13)C与瞬时水分利用效率WUEi的相互关系,目的在于探求δ~(13)C在筛选高水分利用效率毛白杨杂种无性系中的应用价值.结果表明:不同生长时期叶片δ~(13)C值表现为7月<8月<10月<9月,小枝δ~(13)C值表现为8月<9月<10月,叶片δ~(13)C值、小枝δ~(13)C值在不同时期和不同无性系间的差异均达显著水平,无性系间的差异是引起δ~(13)C值变化的主要因素.不同部位碳同位素比值表现为叶片<小枝<根,毛白杨杂种无性系δ~(13)C值在不同部位和无性系间差异均达显著水平,部位间的差异是引起δ~(13)C值变化的主要因素.δ~(13)C值较高的无性系30、83、BL5的WUEi也较高,δ~(13)C值较低的无性系42、26、BT17的WUEi也较低,且不同时期δ~(13)C和WUEi呈较强的正相关,相关系数分别为0.766、0.872、0.675,高δ~(13)C可以作为筛选高WUEi毛白杨的有效指标,且在苗木生长旺盛时期选育能得到更为可靠的结果.     

Quantification and reduction of erroneous differences between images in remote sensing

The reliability of image data, along with the difficulty of accurately comparing images acquired at different times or from different sensors, is a generic problem in remote sensing. Measurement repeatability errors occur frequently and can substantially reduce the system’s ability to reliably quantify real spectral and spatial change in a target. This paper outlines methodologies for quantifying and reducing erroneous differences between monochrome and multispectral or hyperspectral images. [Each of these image types is acquired by an instrument that collects light photons across a variable range of the electromagnetic spectrum (often referred to as an image band). The hyperspectral image is often referred to as a hyperspectral cube with XY spatial dimensions and many Z bands (spectral demotions)]. In this paper, we specifically discuss the Pixel Block Transform (PBT), the Spectral Averaging Transform (SAT), and the Wavelet Transform (WAVEL). We briefly address sensor fusion. Results indicate that the PBT is a powerful cross-noise and repeatability error reducing tool, applicable to monochrome, multispectral, and hyperspectral images. The SAT is as powerful as the PBT in reducing error but is suitable only for hyperspectral imagery. WAVEL can reduce some of the finer scale noise, but it is not as powerful in reducing cross-noise as PBT or SAT and it requires some trial and error for selecting the appropriate wavelet function. It is important that those involved in developing statistically sound relationships between remotely sensed imagery and other data sources understand the problems and their solutions to prevent wasting time or developing relationships that are statistically insignificant or unstable, or that lead to faulty conclusions.     

城乡建设用地景观格局多尺度差异

以郑州市域内1989、2000和2009年的典型城市与农村样地（25 km×25 km）为例,应用空间自相关、半方差、以及九项轨迹方差分析方法,对城市与农村建设用地景观多尺度上的空间格局特征与动态差异进行研究,结果表明,（1）城市建设用地景观聚集强度较高,斑块规模较大,而农村建设用地景观在大部分尺度上呈随机或均匀分布,斑块规模较小。（2）随着尺度的增加,城市及农村建设用地景观分布状态都由聚集向均匀过渡,但前者过渡较为平缓,而后者在小尺度范围（0~2km）变化速度较快,在较大尺度（3~16 km）上其分布状态的波动较小。（3）1989-2009年,城市与农村建设用地景观动态特征有较大差异,并表现出尺度依赖性。城市较小尺度上（0~4 km）建设用地景观的分布状态表现出聚集-分散的趋势,在较大尺度上（8~14 km）表现出分散-聚集的变化趋势。农村小尺度上（0~4 km）建设用地景观的分布状态也表现出聚集-分散的趋势,但大尺度（4~16 km）上状态变化很小且没有规律。     

Scenarios of change in the realized climatic niche of mountain carnivores and ungulates

Mountains are among the natural systems most affected by climate change, and mountain mammals are considered particularly imperiled, given their high degree of specialization to narrow tolerance bands of environmental conditions. Climate change mitigation policies, such as the Paris Agreement, are essential to stem climate change impacts on natural systems. But how significant is the Paris Agreement to the survival of mountain mammals? We investigated how alternative emission scenarios may determine change in the realized climatic niche of mountain carnivores and ungulates in 2050. We based our predictions of future change in species niches based on how species have responded to past environmental changes, focusing on the probabilities of niche shrink and niche stability. We found that achieving the Paris Agreement's commitments would substantially reduce climate instability for mountain species. Specifically, limiting global warming to below 1.5°C would reduce the probability of niche shrinkage by 4% compared with a high-emission scenario. Globally, carnivores showed greater niche shrinkage than ungulates, whereas ungulates were more likely to shift their niches (i.e., face a level of climate change that allows adaptation). Twenty-three species threatened by climate change according to the IUCN Red List had greater niche contraction than other species we analyzed (3% higher on average). We therefore argue that climate mitigation policies must be coupled with rapid species-specific conservation intervention and sustainable land-use policies to avoid high risk of loss of already vulnerable species.     

Predator inspection behaviour in minnow shoals: differences between populations and individuals

Summary When minnows (Phoxinus phoxinus) detect a stalking pike (Esox lucius) one of their first responses is to perform inspection behaviour during which individuals or small groups approach the predator. This paper compares the inspection behaviour of two contrasting groups of minnows: Dorset minnows which have been heavily predated by pike for many thousands of years and Gwynedd minnows which have spent an equivalent period of time in a pike free environment. Minnows sympatric with pike inspected a realistic model pike more frequently and in larger shoals. Although they commenced inspection earlier they were more timid and kept a greater distance between themselves and the predator. After an inspection they were less likely to recommence foraging than minnows from the Gwynedd population. Individual differences in inspection found within the two populations suggest that selfish behaviour was present.