Does intraspecific competition promote variation? A test via synthesis

Competitive diversification, that is, when increasing intraspecific competition promotes population niche expansion, is commonly invoked in evolutionary studies and currently plays a central role in how we conceptualize the process of adaptive diversification. Despite the frequency with which this idea is cited, the empirical evidence for the process is somewhat limited, and the findings of these studies have yet to be weighed objectively through synthesis. Here, we sought to fill this gap by reviewing the existing literature and collecting the data necessary to assess the evidence for competition as a diversifying force. Additionally, we sought to test a more recent hypothesis, which suggests that competition can act to both promote and inhibit dietary diversification depending on the degree to which a consumer depletes its resources. The surprising result of this synthesis was that increasing competition did not have a mean positive effect on population‐level diet breadth or the degree of individual specialization. Instead, we found that increasing intraspecific competition had a restricting effect on population‐level diet breadth in as many cases as it had a diversifying effect. This wide disparity in the effect of competition on consumer diet variation was negatively related to a metric for consumer resource depletion. Altogether, these findings call into question a long‐standing assumption of basic evolutionary models and lend some support to recent theoretical predictions. Specifically, these findings support the idea that competition is primarily diversifying for species with a small effect (per unit biomass) on their resources and that resource depletion limits the diversifying effect of competition for consumers with larger ecological effects.     

A mast‐seeding desert shrub regulates population dynamics and behavior of its heteromyid dispersers

Granivorous rodent populations in deserts are primarily regulated through precipitation‐driven resource pulses rather than pulses associated with mast‐seeding, a pattern more common in mesic habitats. We studied heteromyid responses to mast‐seeding in the desert shrub blackbrush (Coleogyne ramosissima), a regionally dominant species in the Mojave–Great Basin Desert transition zone. In a 5‐year study at Arches National Park, Utah, USA, we quantified spatiotemporal variation in seed resources in mast and intermast years in blackbrush‐dominated and mixed desert vegetation and measured responses of Dipodomys ordii (Ord's kangaroo rat) and Perognathus flavescens (plains pocket mouse). In blackbrush‐dominated vegetation, blackbrush seeds comprised >79% of seed production in a mast year, but 0% in the first postmast year. Kangaroo rat abundance in blackbrush‐dominated vegetation was highest in the mast year, declined sharply at the end of the first postmast summer, and then remained at low levels for 3 years. Pocket mouse abundance was not as strongly associated with blackbrush seed production. In mixed desert vegetation, kangaroo rat abundance was higher and more uniform through time. Kangaroo rats excluded the smaller pocket mice from resource‐rich patches including a pipeline disturbance and also moved their home range centers closer to this disturbance in a year of low blackbrush seed production. Home range size for kangaroo rats was unrelated to seed resource density in the mast year, but resource‐poor home ranges were larger (P < 0.001) in the first postmast year, when resources were limiting. Blackbrush seeds are higher in protein and fat but lower in carbohydrates than the more highly preferred seeds of Indian ricegrass (Achnatherum hymenoides) and have similar energy value per unit of handling time. Kangaroo rats cached seeds of these two species in similar spatial configurations, implying that they were equally valued as stored food resources. Blackbrush mast is a key resource regulating populations of kangaroo rats in this ecosystem.     

Balancing competition for resources with multiple pest regulation in diversified agroecosystems: a process‐based approach to reconcile diversification and productivity

Agroecosystem plant diversification can enhance pest biological regulation and is a promising alternative to pesticide application. However, the costs of competition for resources between plants may exceed the benefits gained by pest regulation. To disentangle the interactions between pest regulation and competition, we developed a generic process‐based approach that accounts for the effects of an associated plant and leaf and root pests on biomass production. We considered three crop–plant associations that differ in competition profiles, and we simulated biomass production under wide ranges of both pest regulation rates and resources’ availability. We analyzed outputs to quantify the pest regulation service level that would be required to attain monoculture yield and other production goals. Results showed that pest regulation requirements were highly dependent on the profile of resource interception of the associated plant and on resources’ availability. Pest regulation and the magnitude of competition between plants interacted in determining the balance between nitrogen and radiation uptake by the crop. Our findings suggest that productivity of diversified agroecosystems relative to monoculture should be optimized by assembling plants whose characteristics balance crops’ resource acquisition. The theoretical insights from our study draw generic rules for vegetation assemblage to optimize trade‐offs between pest regulation and production. Our findings and approach may have implications in understanding, theorizing and implementing agroecosystem diversification. By its generic and adaptable structure, our approach should be useful for studying the effects of diversification in many agroecosystems.     

Territory Availability at Different Spatial Scales does not Affect Fighting Investment in Males of the Lycaenid Butterfly Strymon mulucha

In territorial species, rivals investment in fights over territories may increase when the availability of suitable areas for defense is low. This should occur because low territory availability may increase the costs to maintain and acquire territories. Although such process occurs in small spatial scales (local scale), territory availability in larger scales (regional scale) may also affect fighting investment, as losers should incur additional dispersing costs to find new territories. In this study, we used males of the hilltopping butterfly Strymon mulucha to evaluate the hypothesis that males should invest more in territorial fights when the costs to find new territories are higher (both at local and at regional scale). We timed male–male contests for territories located in 12 hilltops and measured male density per territory in each hilltop (local scale). We also quantified the distance between hilltops containing suitable areas for territories (regional scale). Male–male contests lasted 21 s on average, and copulations did not occur during the observations. The duration of contests was unrelated to the male density per territory or to the distance among hilltops, indicating that the investment in fights was unaffected by the availability of territorial sites, independent of the spatial scale. As male–male contests in S. mulucha are longer than the mean contest duration in other butterfly species and mating is extremely rare, we suggest that the value of each territory may be high enough to favor males that always invest as much as possible in contests.     

Niche partitioning due to adaptive foraging reverses effects of nestedness and connectance on pollination network stability

Much research debates whether properties of ecological networks such as nestedness and connectance stabilise biological communities while ignoring key behavioural aspects of organisms within these networks. Here, we computationally assess how adaptive foraging (AF) behaviour interacts with network architecture to determine the stability of plant–pollinator networks. We find that AF reverses negative effects of nestedness and positive effects of connectance on the stability of the networks by partitioning the niches among species within guilds. This behaviour enables generalist pollinators to preferentially forage on the most specialised of their plant partners which increases the pollination services to specialist plants and cedes the resources of generalist plants to specialist pollinators. We corroborate these behavioural preferences with intensive field observations of bee foraging. Our results show that incorporating key organismal behaviours with well‐known biological mechanisms such as consumer‐resource interactions into the analysis of ecological networks may greatly improve our understanding of complex ecosystems.     

Assessing hydrologic alteration: Evaluation of different alternatives according to data availability

The natural flow regime of rivers across the world has been largely modified. Understanding the extent to which the flow regime deviates from natural conditions is necessary for designing sound management and restoration measures. In this regard, ‘Indicators of Hydrologic Alteration’ is currently considered one of the most effective approaches for assessing hydrologic alteration (HA). However, several generalized drawbacks such as the climatic variability between the pre- and post-impacted series and the scarcity of hydrological data in many impaired rivers should be addressed. In this study, a protocol with the following five alternative designs based on data availability is presented: (1) Paired-Before–After Control–Impact (BACIP), (2) Before–After (BA), (3) Control–Impact (CI), (4) Hydrological Classification (HC) and (5) Predicted Hydrological indices (HP). BACIP compares the status of the impacted gauge before and after the perturbation is started, in addition to controlling for natural climatic changes. Hence, it has been considered as the reference benchmark for all other designs. When this protocol was applied to 11 reservoirs situated in the northern third of the Iberian Peninsula, the BA design was able to correctly identify most of the non-significant HA but failed in almost one quarter of the significant alterations. Similarly, BACIP and CI showed an agreement of >80%. This suggests that the method is suitable when proper data are unavailable for BACIP or BA. In addition, our results indicated that the critical thresholds for HA varied depending on the hydrological index being considered. Significant HAs ranged from <5% for the number of days with increasing and decreasing flows to >64% for the duration of low-flow pulses. To delineate adequate thresholds, further research combining hydrological analyses with the biological response to the HA is warranted. Finally, the application of HC and HP designs revealed a significant degree of uncertainty related to the intra-class variability and the predictive error of the models. Therefore, 25% of the analysis could not be evaluated. However, in the evaluable cases, the HC and HP designs correctly assessed >75% of the HA, which highlighted the potential of this method in cases of scarce streamflow data.     

5种甘草属植物花序和种子生产的位置效应及繁殖资源分配模式初步研究

以种植于新疆石河子的光果甘草( Glycyrrhiza glabra Linn.)、胀果甘草( G. inflata Batal.)、乌拉尔甘草( G. uralensis Fisch.)、黄甘草( G. eurycarpa P. C. Li)和蜜腺甘草( G. glabra var. glandulosa X. Y. Li)为研究对象,对植株不同部位的花序数量、花序正常发育率、每花序单花数量和果穗干质量,以及植株不同部位和花序不同部位的生物量投入比、座果率、结籽率、种子投影面积和种子千粒质量进行测定;在此基础上,对供试5种甘草属( Glycyrrhiza Linn.)植物的繁殖资源分配模式和种子生产策略进行分析。结果表明：同一植株内,光果甘草、乌拉尔甘草、黄甘草和蜜腺甘草的花序数量、花序正常发育率、每花序单花数量和果穗干质量从植株下部到上部总体上依次递减,而胀果甘草植株不同部位间这4项指标总体上无显著差异。同一植株内,胀果甘草植株中部的生物量投入比和座果率均较高,但其生物量投入比、座果率和结籽率在植株不同部位间均无显著差异;而供试另4种植物的生物量投入比、座果率和结籽率从植株下部到上部总体上依次递减。同一花序内,胀果甘草花序中部的生物量投入比明显高于花序上部和下部,座果率从花序下部到上部依次递减,结籽率则在花序不同部位间无显著差异,而供试另4种植物的生物量投入比、座果率和结籽率从花序下部到上部总体上依次递减。供试5种植物的种子投影面积和种子千粒质量在植株不同部位间和花序不同部位间均无显著差异。综合研究结果显示：在资源竞争、结构效应和花粉限制的影响下,供试5种甘草属植物存在2种不同的资源分配模式和种子生产格局。其中,光果甘草、乌拉尔甘草、黄甘草和蜜腺甘草通过减少对晚发育的花或果实的资源投入来保障早发育的花或果实获得较多的资源,达到繁殖成功的目的;而胀果甘草则采取对花和果实随机败育的方式减小资源竞争的压力,这2种繁殖资源分配模式和种子生产策略对提高甘草属植物的繁殖成功率具有重要作用。     

风景园林与绿色基础设施在城市流域水资源规划中的重要作用

通过绿色基础设施途径,处理美国波士顿北部的马萨诸塞州城市流域的水资源规划问题。从多个尺度为风景园林师提供水资源规划的经验与启发,探究公众对新型绿色基础设施解决方案的态度与偏好,以及公众偏好对于整体规划设计的重要作用。     

融于自然、展现风景——美国国家公园道路系统建设历程与经验启示

在中国国家公园体制试点工作不断推进的当下,探讨国家公园内基础设施的建设显得敏感而有必要。在梳理美国国家公园道路系统发展建设历程的基础上,总结提炼出其在前期论证、建设理念以及多部门合作等方面的经验。同时就如何统筹交通游赏需求与资源保护之间的关系也做了有益的探讨,对中国未来国家公园的发展建设乃至自然资源的保护和利用都具有较为重要的参考和借鉴意义。