Zimbabwean Students' Conceptions of Selected Ecological Concepts

Understanding Food Chains and Food Webs, 1700–1970

When discussing ecology and environmental awareness, we frequently tell our students that all are mutually dependent and that if one element of an environment is disturbed, there are many, often farreaching consequences for all organisms within that environment. That said, we quickly move on to another topic, thinking that we have increased our students' knowledge about their environment and factors affecting environmental change. We can better help our students understand the interrelatedness of if we can help them to see why are interdependent. Charles Elton (1927), a pioneering animal ecologist, suggests that the structure and activities of animal communities primarily depend on food supply. McInerney (1993) concurs, noting that in nature everyone is someone else's dinner (p. 293). These remarks suggest that all are part of an intricate food and survival chain in which they obtain necessary nutrients directly or indirectly from other (Goodwin 1992). The movement of nutrients and energy among and the resulting interactions are typically represented by food chains or webs (Krebs 1988; Ricklefs 1990; Smith 1980). The structure of a food web is based on the functional relationship of three groups of organisms: autotrophs, heterotrophs and decomposers (which are really heterotrophs but are given their own category because of their nutrient recycling role). Each of these groups relies, directly or indirectly, on the others for attaining their essential nutrients and energy. Even though the movement of nutrients and energy between any two depends on one eating the other, the overall flow pattern for each within the food web is fundamentally different. Nutrients can cycle through the food web an infinite number of times, whereas energy can only flow through the web once (or in some cases, with minimal cycling among the heterotrophs). We often teach the concepts of food chains and webs using lectures supplemented with various diagrams showing the simplicity and/or complexity of various food webs. Students in these situations often fail to see the dynamic interactions among the that make up the food web, as well as the impact of environmental disturbances on the organisms in the food web. Teaching food webs is a perfect opportunity to supplement student learning with student doing. The activity we describe is one that can be used to teach the dynamic nature of food webs and to demonstrate the impact of environmental disturbances on the within a food web to students of all ages. By having students become a member of a food web and actually seek its nutrients from the other living things around it, the students model the behaviors they and other display on a daily basis. The result of this activity is a greater understanding of and appreciation for the interdependencies of things.

Measuring in situ nutrient and energy flows in spatially and temporally complex aquatic ecosystems represents a major ecological challenge. Food web structure, energy and nutrient budgets are difficult to measure, and it is becoming more important to quantify both energy and nutrient flow to determine how food web processes and structure are being modified by multiple stressors. We propose that polychlorinated biphenyl (PCB) congeners represent an ideal tracer to quantify in situ energy and nutrient flow between trophic levels. Here, we demonstrate how an understanding of PCB congener bioaccumulation dynamics provides multiple direct measurements of energy and nutrient flow in aquatic food webs. To demonstrate this novel approach, we quantified nitrogen (N), phosphorus (P) and caloric turnover rates for Lake Huron lake trout, and reveal how these processes are regulated by both growth rate and fish life history. Although minimal nutrient recycling was observed in young growing fish, slow growing, older lake trout (>5 yr) recycled an average of 482 Tonnes·yr(-1) of N, 45 Tonnes·yr(-1) of P and assimilated 22 TJ yr(-1) of energy. Compared to total P loading rates of 590 Tonnes·yr(-1), the recycling of primarily bioavailable nutrients by fish plays an important role regulating the nutrient states of oligotrophic lakes.

Food Chains and Food Webs

Food webs are complex ecological networks that reveal species interactions and energy flow in ecosystems. Prevailing ecological knowledge on forested streams suggests that their food webs are based on allochthonous carbon, driven by a constant supply of organic matter from adjacent vegetation and limited primary production due to low light conditions. Extreme climatic disturbances can disrupt these natural ecosystem dynamics by altering resource availability, which leads to changes in food web structure and functioning. Here, we quantify the response of stream food webs to two major hurricanes (Irma and María, Category 5 and 4, respectively) that struck Puerto Rico in September 2017. Within two tropical forested streams (first and second order), we collected ecosystem and food web data 6 months prior to the hurricanes and 2, 9, and 18 months afterward. We assessed the structural (e.g., canopy) and hydrological (e.g., discharge) characteristics of the ecosystem and monitored changes in basal resources (i.e., algae, biofilm, and leaf litter), consumers (e.g., aquatic invertebrates, riparian consumers), and applied Layman's community-wide metrics using the isotopic composition of 13 C and 15 N. Continuous stream discharge measurements indicated that the hurricanes did not cause an extreme hydrological event. However, the sixfold increase in canopy openness and associated changes in litter input appeared to trigger an increase in primary production. These food webs were primarily based on terrestrially derived carbon before the hurricanes, but most taxa (including Atya and Xiphocaris shrimp, the consumers with highest biomass) shifted their food source to autochthonous carbon within 2 months of the hurricanes. We also found evidence that the hurricanes dramatically altered the structure of the food web, resulting in shorter (i.e., smaller food-chain length), narrower (i.e., lower diversity of carbon sources) food webs, as well as increased trophic species packing. This study demonstrates how hurricane disturbance can alter stream food webs, changing the trophic base from allochthonous to autochthonous resources via changes in the physical environment (i.e., canopy defoliation). As hurricanes become more frequent and severe due to climate change, our findings greatly contribute to our understanding of the mechanisms that maintain forested stream trophic interactions amidst global change.

Food webs

Lakes and reservoirs play key roles in global carbon cycling, especially as a carbon sink. Enrichment of nutrients in lakes and reservoirs (eutrophication) and rising global temperatures favors the proliferation of bloom-forming cyanobacteria. Harmful blooms of cyanobacteria (cyanoHABs) alter carbon and nutrient cycling in freshwater ecosystems. Some evidence suggests the introduction or establishment of invasive mussel species (i.e., Dreissena spp.) also favor cyanoHAB formation through selective filter feeding, a process through which they may also impact biogeochemical processes including carbon cycling and sequestration. However, few studies have considered the combined effects of invasive mussels and cyanoHABs on carbon and nitrogen cycling in freshwater ecosystems. Here, we examined microbial community composition and biogeochemical attributes (including carbon and nitrogen stable isotopes) in eutrophic lakes, reservoirs, and rivers in western Ohio, eastern Indiana, and northern Kentucky during the cyanobacterial bloom period of the summer of 2015. Our samples include both sites impacted by invasive mussels and those where invasive mussels have not yet been observed. Based on 16S and 18S rRNA gene sequence analysis, we found that cyanobacterial and algal communities varied across sites and were most closely related to habitat (sediment or water column sample) and site, regardless of the presence of invasive mussels or other environmental factors. However, we did find evidence that invasive mussels may influence both carbon and nitrogen cycling. While the results are based on a single time point sampling, they highlight the interactions of multiple environmental stressors in aquatic ecosystems and the critical need for more temporally intensive studies of carbon and nutrient cycling in bloom- and mussel-impacted waters.

Protozoa-driven micro-food webs are pivotal regulators of microbial community structure and carbon-nitrogen cycling. By mediating trophic cascades that regulate bacterial and algal populations, protozoa influence nutrient remineralization and energy flow. Their regulation is crucial for stabilizing biogeochemical processes and preventing harmful algal blooms. However, little is known about the detailed relationship between the traits of micro-food webs and carbon/nitrogen cycling processes. Using metagenomic data, we investigated the complexity and stability of micro-food webs in three distinct zones of the Fenhe Reservoir-the inflow river zone, shallow wetland, and deep-water zone-to assess their impacts on carbon and nitrogen cycling. Our findings revealed distinct spatial patterns in micro-food web complexity and stability, with the highest diversity and interaction density in inflowing river zones and a gradual simplification towards deep-water zones. Functional gene analysis shows significant differences in carbon degradation, fixation pathways, and nitrogen transformation processes, with shallow waters exhibiting strong microbial-mediated nitrification and denitrification, while deep waters rely on anaerobic nitrogen reduction pathways. Partial least squares path modeling (PLS-PM) indicated that protozoan-driven micro-food web structures regulate microbial functional differentiation, thereby influencing carbon and nitrogen cycle. Additionally, environmental parameters such as organic carbon concentration and nitrogen availability significantly shape microbial interactions and biogeochemical transformations. These findings highlight the intricate relationship between microbial community composition, food web stability, and elemental cycling, providing critical insights for reservoir ecosystem management and water quality optimization.

The interdependency of relationships and energy flow in ecosystems are crucial biological concepts that students frequently find hard to understand. They are one of the foundations to the survival of living things and the complex processes that balance life on Earth. The ability to interpret food chains and food webs is fundamental in the communication and understanding of relationships between organisms in the domain of biology. I examine the ways elementary-level students read a simple food web diagram and the effect this has on their understanding of the encapsulated biology concepts. Diagram reading approaches are described along with analysis of how meaning making is influenced by students' preconceived ideas. The results indicate the students experienced a range of difficulties in reading the food web diagram. I conclude that food web instruction must address prior knowledge, challenge preconceptions, and involve deep diagram processing. The research provides insights into the difficulties high school students have in comprehending food webs and understanding relationships in ecosystems.

This article investigates the conditions under which consumers maximize matter and energy flow in ecosystems, using a simple, general, abstract nutrient-limited ecosystem model. The model is analyzed for several functional forms of trophic interactions. The conditions for enhancement of energy flow by consumers are found to be qualitatively the same in all cases. The first and most important condition is that consumers act to accelerate the circulation of matter within the ecosystem; more precisely, the mean transit time of nutrients in the path consumers-decomposers-nutrient pool must be sufficiently smaller than their mean transit time in the path producers-decomposers-nutrient pool. The second condition is that the total quantity of nutrients in the ecosystem must be higher than some threshold value. The third condition is that consumption rate must be moderate. These conditions being usually met, it is likely that consumers as a whole do generally play a role of maximizers of matter and energy flow in stable natural ecosystems.

PDF HTML阅读 XML下载 导出引用 引用提醒 食物链长度理论研究进展 DOI: 10.5846/stxb201209181312 作者: 作者单位: 中国科学院水生生物研究所,中国科学院水生生物研究所,中国科学院水生生物研究所,中国科学院水生生物研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目（31170439）；国家科技重大专项资助项目（2012ZX07101-001-04，2012ZX07501-001-06） Food chain length theory：a review Author: Affiliation: Institute of Hydrobiology,Chinese Academy of Sciences,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:食物链长度（Food chain length，FCL）是生态系统中最重要的特点之一，它通过改变生物间的营养关系，影响着生物多样性，群落的结构以及稳定性；它是反映食物网物质转换与能量传递的综合指数，食物链及其动态特征是生态学许多重要理论的基础，食物链长度理论的研究进展，推动了人们对水域生态系统中生物和非生物相互作用的理解。回顾了食物链长度的3种度量方法及其详细的计算方法，在此基础上简述了各方法的特点。综述了食物链长度的决定因素的4种假说（资源可利用性假说、生产力空间假说、生态系统大小假说、动态稳定性假说）及其交互作用，重点总结了湖泊食物链长度的空间格局与决定因素的研究进展。最后，食物链长度研究展望，包括食物链长度决定因子研究存在的问题及发展方向的总结，以及在在水域生态学中的应用的研究进展，例如食物链长度在指示污染物的生物富集中的研究进展、食物链食物链长度在指导生物操作、以及在食物链长度在对气候变化响应方面的研究进展等等。 Abstract:Food-chain length (FCL)is a significant ecosystem index. It can influence the biodiversity, pattern and stability of the biological community by altering trophic interactions within it. Food chains are caricatures of communities that trace linear either energy or the effect strength pathways from primary producers to apex predators embedded within more complex food webs. And Food chains are also the basis for many important concepts in ecology. In the last few years, innovative process-level studies have been expanding rapidly. Food chain length theory to ecological research is becoming increasing common and to significant new levels of understanding of ecological processes and elemental fluxes through biological and abiotic systems. Food webs represent a road map of feeding relationships in ecological community and can be defined in at least three different ways. we defined three commonly used operational definitions of FCL and reviewed the method measuring of the three kind of food chain length including the characteristics. Conventional wisdom holds that either resource availability or disturbance limit food-chain length; however, new researches and new techniques challenge the conventional wisdom and broaden the discourse on food-chain length. We reviewed four hypotheses on the determinant of FCL including resource availability hypothesis, productivity space hypothesis, ecosystem size hypothesis and dynamic stability hypothesis and the relation among these hypotheses. In this article, we discussed the evidence for controls on FCL in freshwater ecosystems. Recent results suggest that resource availability limits food-chain length only in system that the resource availability is very low. Different defines of ecosystem size can cause different result about the ecosystem size hypothesis. And ecosystem size controls food chain length only at local region, while at the global pattern the relationship between ecosystem size and food chain length is very weak. The independence and interaction between four hypotheses indicate the complexity and diversity of food chain length controls in ecosystems. Food-web structure is closely relevant to the functioning of ecosystems. We further synthesized the spatial pattern and determinants of FCL in lake ecosytems as a empirical complementation to the theoretical study. So the factors that control or alter food webs are more and more considered in managing, conserving, and restoring aquatic ecosystems. At the last part of this study, we reviewed the problems in the recent research on this issue and looked into the meaningful research in the future including movement of contaminants, biomanipulation, and climate change, several important areas of use of basic food-web research in applied issues. 参考文献 相似文献 引证文献

Understanding carbon cycling in blue carbon ecosystems is key to sequestrating more carbon in these ecosystems to mitigate climate change. However, limited information is available on the basic characteristics of publications, research hotspots, research frontiers, and the evolution of topics related to carbon cycling in different blue carbon ecosystems. Here, we conducted bibliometric analysis on carbon cycling in salt marsh, mangrove, and seagrass ecosystems. The results showed that interest in this field has dramatically increased with time, particularly for mangroves. The USA has substantially contributed to the research on all ecosystems. Research hotspots for salt marshes were sedimentation process, carbon sequestration, carbon emissions, lateral carbon exchange, litter decomposition, plant carbon fixation, and carbon sources. In addition, biomass estimation by allometric equations was a hotspot for mangroves, and carbonate cycling and ocean acidification were hotspots for seagrasses. Topics involving energy flow, such as productivity, food webs, and decomposition, were the predominant areas a decade ago. Current research frontiers mainly concentrated on climate change and carbon sequestration for all ecosystems, while methane emission was a common frontier for mangroves and salt marshes. Ecosystem-specific research frontiers included mangrove encroachment for salt marshes, ocean acidification for seagrasses, and aboveground biomass estimation and restoration for mangroves. Future research should expand estimates of lateral carbon exchange and carbonate burial and strengthen the exploration of the impacts of climate change and restoration on blue carbon. Overall, this study provides the research status of carbon cycling in vegetated blue carbon ecosystems, which favors knowledge exchanges for future research.

Characterization of energy flow in ecosystems is one of the primary goals of ecology, and the analysis of trophic interactions and food web dynamics is key to quantifying energy flow. Predator-prey interactions define the majority of trophic interactions and food web dynamics, and visual analysis of stomach, gut or fecal content composition is the technique traditionally used to quantify predator-prey interactions. Unfortunately such techniques may be biased and inaccurate due to variation in digestion rates (Sheppard & Hardwood 2005); however, those limitations can be largely overcome with new technology. In the last 20 years, the use of molecular genetic techniques in ecology has exploded (King et al. 2008). The growing availability of molecular genetic methods and data has fostered the use of PCR-based techniques to accurately distinguish and identify prey items in stomach, gut and fecal samples. In this month's issue of Molecular Ecology Resources, Corse et al. (2010) describe and apply a new approach to quantifying predator-prey relationships using an ecosystem-level genetic characterization of available and consumed prey in European freshwater habitats (Fig. 1a). In this issue of Molecular Ecology, Hardy et al. (2010) marry the molecular genetic analysis of prey with a stable isotope (SI) analysis of trophic interactions in an Australian reservoir community (Fig. 1b). Both papers demonstrate novel and innovative approaches to an old problem--how do we effectively explore food webs and energy movement in ecosystems?

Despite escalating anthropogenic alteration of food webs, how the carbon cycle in ecosystems is regulated by food web processes remains poorly understood. We quantitatively synthesize the effects of consumers (herbivores, omnivores and carnivores) on the carbon cycle of coastal wetland ecosystems, 'blue carbon' ecosystems that store the greatest amount of carbon per unit area among all ecosystems. Our results reveal that consumers strongly affect many processes of the carbon cycle. Herbivores, for example, generally reduce carbon absorption and carbon stocks (e.g. aboveground plant carbon by 53% and aboveground net primary production by 23%) but may promote some carbon emission processes (e.g. litter decomposition by 32%). The average strengths of these effects are comparable with, or even times higher than, changes driven by temperature, precipitation, nitrogen input, CO2 concentration, and plant invasions. Furthermore, consumer effects appear to be stronger on aboveground than belowground carbon processes and vary markedly with trophic level, body size, thermal regulation strategy and feeding type. Despite important knowledge gaps, our results highlight the powerful impacts of consumers on the carbon cycle and call for the incorporation of consumer control into Earth system models that predict anthropogenic climate change and into management strategies of Earth's carbon stocks. This article is part of the theme issue 'Integrative research perspectives on marine conservation'.

The Arctic is the world’s largest reservoir of soil organic carbon and understanding biogeochemical cycling in this region is critical due to the potential feedbacks on climate. However, our knowledge of carbon (C) and nitrogen (N) cycling in the Arctic is incomplete, as studies have focused on plants, detritus, and microbes but largely ignored their consumers. Here we construct a comprehensive Arctic food web based on functional groups of microbes (e.g., bacteria and fungi), protozoa, and invertebrates (community hereafter referred to as the invertebrate food web) residing in the soil, on the soil surface and within the plant canopy from an area of moist acidic tundra in northern Alaska. We used an energetic food web modeling framework to estimate C flow through the food web and group-specific rates of C and N cycling. We found that 99.6% of C processed by the invertebrate food web is derived from detrital resources (aka ‘brown’ energy channel), while 0.06% comes from the consumption of live plants (aka ‘green’ energy channel). This pattern is primarily driven by fungi, fungivorous invertebrates, and their predators within the soil and surface-dwelling communities (aka the fungal energy channel). Similarly, >99% of direct invertebrate contributions to C and N cycling originate from soil- and surface-dwelling microbes and their immediate consumers. Our findings demonstrate that invertebrates from within the fungal energy channel are major drivers of C and N cycling and that changes to their structure and composition are likely to impact nutrient dynamics within tundra ecosystems.