Ecosystem Engineering Activities Research Articles

Are hippos Africa's most influential megaherbivore? A review of ecosystem engineering by the semi-aquatic common hippopotamus.

Megaherbivores perform vital ecosystem engineering roles, and have their last remaining stronghold in Africa. Of Africa's remaining megaherbivores, the common hippopotamus (Hippopotamus amphibius) has received the least scientific and conservation attention, despite how influential their ecosystem engineering activities appear to be. Given the potentially crucial ecosystem engineering influence of hippos, as well as mounting conservation concerns threatening their long-term persistence, a review of the evidence for hippos being ecosystem engineers, and the effects of their engineering, is both timely and necessary. In this review, we assess, (i) aspects of hippo biology that underlie their unique ecosystem engineering potential; (ii) evaluate hippo ecological impacts in terrestrial and aquatic environments; (iii) compare the ecosystem engineering influence of hippos to other extant African megaherbivores; (iv) evaluate factors most critical to hippo conservation and ecosystem engineering; and (v) highlight future research directions and challenges that may yield new insights into the ecological role of hippos, and of megaherbivores more broadly. We find that a variety of key life-history traits determine the hippo's unique influence, including their semi-aquatic lifestyle, large body size, specialised gut anatomy, muzzle structure, small and partially webbed feet, and highly gregarious nature. On land, hippos create grazing lawns that contain distinct plant communities and alter fire spatial extent, which shapes woody plant demographics and might assist in maintaining fire-sensitive riverine vegetation. In water, hippos deposit nutrient-rich dung, stimulating aquatic food chains and altering water chemistry and quality, impacting a host of different organisms. Hippo trampling and wallowing alters geomorphological processes, widening riverbanks, creating new river channels, and forming gullies along well-utilised hippo paths. Taken together, we propose that these myriad impacts combine to make hippos Africa's most influential megaherbivore, specifically because of the high diversity and intensity of their ecological impacts compared with other megaherbivores, and because of their unique capacity to transfer nutrients across ecosystem boundaries, enriching both terrestrial and aquatic ecosystems. Nonetheless, water pollution and extraction for agriculture and industry, erratic rainfall patterns and human-hippo conflict, threaten hippo ecosystem engineering and persistence. Therefore, we encourage greater consideration of the unique role of hippos as ecosystem engineers when considering the functional importance of megafauna in African ecosystems, and increased attention to declining hippo habitat and populations, which if unchecked could change the way in which many African ecosystems function.

Mussels drive polychlorinated biphenyl (PCB) biomagnification in a coastal food web

Despite international regulation, polychlorinated biphenyls (PCBs) are routinely detected at levels threatening human and environmental health. While previous research has emphasized trophic transfer as the principle pathway for PCB accumulation, our study reveals the critical role that non-trophic interactions can play in controlling PCB bioavailability and biomagnification. In a 5-month field experiment manipulating saltmarsh macro-invertebrates, we show that suspension-feeding mussels increase concentrations of total PCBs and toxic dioxin-like coplanars by 11- and 7.5-fold in sediment and 10.5- and 9-fold in cordgrass-grazing crabs relative to no-mussel controls, but do not affect PCB bioaccumulation in algae-grazing crabs. PCB homolog composition and corroborative dietary analyses demonstrate that mussels, as ecosystem engineers, amplify sediment contamination and PCB exposure for this burrowing marsh crab through non-trophic mechanisms. We conclude that these ecosystem engineering activities and other non-trophic interactions may have cascading effects on trophic biomagnification pathways, and therefore exert strong bottom-up control on PCB biomagnification up this coastal food web.

The effects of dryland cropping system intensity on soil function and associated changes in macrofauna communities

AbstractCrop production in water‐limited environments may be enhanced through improved soil function by facilitating precipitation capture and erosion control. Soil macrofauna are known to support improved soil structure and water dynamics through ecosystem engineering activities, and their populations can be influenced by management. We examined the effect of bare summer fallow frequency on soil macrofauna communities and soil physical properties in a long‐term (32‐yr) dryland no‐till agroecosystem experiment at two sites in eastern Colorado, USA. Treatments represented a gradient of fallow frequency and organic matter inputs, which included wheat (Triticum aestivum L.)–fallow, wheat–corn (Zea mays L.)–fallow, and continuously cropped with no planned summer fallow. The design also included a perennial grass treatment with minimal management consisting of six native grasses. We observed links between soil macrofauna and soil functional metrics, particularly related to soil aggregation and water infiltration. There was a trend toward higher macrofauna populations and soil function with increased cropping system intensity, and perennial grass outperformed the cropped treatments significantly for most soil health parameters. Multivariate analyses revealed that different treatments support relatively distinct macrofauna communities. Our results suggest that soil macrofauna populations may be important facilitators of soil structure and associated water dynamics in dryland no‐till agroecosystems and respond positively to reduced fallow and higher organic inputs.

Beavers as ecosystem engineers – a review of their positive and negative effects

The paper reviews the environmental activity of beavers (Castor fiber L. and Castor canadensis L.) and their impact on different aspects of the environment. Beavers inhabit almost all climatic zones but are most abundant in Russia, USA, and Canada. Beavers’ ecosystem engineering activities include building dams and creating ponds. The dams provoke hydrological alteration, soil overwetting, changes in local micro- and nanorelief. The water stagnation in beaver ponds below dams results in lack of oxygen, a high carbon concentration, and the death of many aquatic organisms. The flooding water above the dam causes vegetation death due to overwetting and at the same time a rise in the biodiversity of water organisms. This paper includes original data gathered by Tomsk State University on lack of oxygen and subsequent fish death in dammed ponds. All environmental changes are cumulative and have strong contextual dependence. The beavers’ environmental activity has positive and negative consequences.

Human paths have positive impacts on plant richness and diversity: A meta-analysis.

We assess the impacts of human paths, trails, and roads on plant species richness and Shannon diversity. Most reviews of this topic have not considered community‐level measures and have focused on excessive tourism impacts. We found significant positive effects of paths on plant richness and diversity. The effect size for richness was highest when studies included roads (paved) or trails (unpaved). The effect size found for diversity was highest when studies were in grasslands. We also found experimental designs comparing high levels of path use to low levels of path use, near‐to‐path versus far‐from‐path and path‐presence versus path‐absence comparisons obtained the largest effect sizes. There was no evidence that non‐native species explained most increases in species richness or diversity. The effect sizes of human paths on plant communities are comparable in magnitude to those reported for other mammals’ disturbance and ecosystem engineering activities.

A geospatial analysis of ecosystem engineer activity and its use during species reintroduction

The Scottish Government has announced that they are minded to allow reintroduced populations of Eurasian beaver (Castor fiber), an ecosystem engineer, to remain in Scotland. Some species and habitats of conservation importance may be affected by the activities of an ecosystem engineer. The study had two key objectives: to identify the potential location of the beaver’s two ecosystem engineering activities and to assess risks to vulnerable habitats and species. To identify potential core beaver woodland, a rule-based species distribution model was developed which included a novel method of integrating beaver territory size requirements. This was used to further predict where beavers would be unlikely to dam. We used the models to assess the spatial overlap between ecosystem engineering activities (i.e. herbivory and damming) with habitats and species of conservation importance. One hundred and five thousand five hundred eighty-six hectares of core beaver woodland was identified, which predicted the location of beaver herbivory. Our model successfully predicted the location of beaver activities surveyed in the largest beaver population in Scotland. Extensive overlap was predicted between beaver herbivory and habitats of conservation importance, in particular aspen woodland, Atlantic hazelwood, and alluvial forests. Eighty-seven percent of watercourses in Scotland were outside the beaver damming model, and hence had a lower likelihood of being dammed. The majority of freshwater pearl mussel, lamprey and Atlantic salmon Special Areas of Conservation, were in river sections less likely to be dammed. If beavers recolonise their former range in Scotland, ecosystem engineering activities are likely to be extensive. However, any impacts on vulnerable species and habitats will be in specific areas and will need to be monitored.

Restructuring of nutrient flows in island ecosystems following human colonization evidenced by isotopic analysis of commensal rats

The role of humans in shaping local ecosystems is an increasing focus of archaeological research, yet researchers often lack an appropriate means of measuring past anthropogenic effects on local food webs and nutrient cycling. Stable isotope analysis of commensal animals provides an effective proxy for local human environments because these species are closely associated with human activities without being under direct human management. Such species are thus central to nutrient flows across a range of socionatural environments and can provide insight into how they intersected and transformed over time. Here we measure and compare stable carbon and nitrogen isotope data from Pacific rat (Rattus exulans) skeletal remains across three Polynesian island systems [Mangareva, Ua Huka (Marquesas), and the Polynesian Outlier of Tikopia] during one of the most significant cases of human migration and commensal introduction in prehistory. The results demonstrate widespread δ15N declines across these islands that are associated with human land use, intensification, and faunal community restructuring. Local comparison of rat stable isotope data also tracks human activities and resource availability at the level of the settlement. Our results highlight the large-scale restructuring of nutrient flows in island ecosystems that resulted from human colonization and ecosystem engineering activities on Pacific islands. They also demonstrate that stable isotope analysis of often-ignored commensal taxa can provide a tool for tracking human land use and environmental effects.

Contribution of the nutrient-enriched ant nest debris soil to growth and yield of Kalmegh (Andrographis paniculata) under natural and experimental field conditions

Andrographis paniculata, commonly known as Kalmegh, is an important medicinal plant which exhibits a range of pharmacological characteristics. The present study revealed that under natural and experimental field conditions, the debris soil of the ground-nesting ant (Pheidole latinoda) colonies increased soil fertility and yield of this plant. The growth of Kalmegh planted in the debris amended soil was significantly enhanced in a dose-dependent manner. The yield, in terms of number of branches, number of leaves, plant biomass and number of pods plant−1 was consistently higher for plants grown in debris amended treatments as compared with plants grown in control soil. Concentrations of total C, P, available N (NH4-N, NO3-N) and microbial biomass C and P were significantly higher in the various debris amended soil treatments as compared with the control soil. Significant positive correlations were found between the ecophysiological traits of Kalmegh plants, i.e. leaf area, total biomass and number of fruits plant−1, and the soil chemical properties of the soil. Under natural field conditions also the biomass of Kalmegh plants growing within 5 m distance of P. latinoda nests was significantly higher as compared with plants located at a distance >10 m. Overall, the results suggested that the ecosystem engineering activities of P. latinoda colonies have the potential to contribute to soil fertility and thereby promote enhanced growth and yield of this medicinally important plant. Since colonies of ground-nesting ant species, such as P. latinoda, are abundant in annual cropping systems, they can contribute to agricultural sustainability.

Heavy metal accumulation and ecosystem engineering by two common mine site-nesting ant species: implications for pollution-level assessment and bioremediation of coal mine soil.

The present study focuses on the abundance, heavy metal content, and the impact of ecosystem engineering activities of two coal mine site-inhabiting ant species, Cataglyphis longipedem and Camponotus compressus. The abundance of Ct. longipedem increased while that of C. compressus decreased, with increasing soil pollution. Correspondence analysis reveals a close association between soil heavy metal concentrations and Ct. longipedem abundance, but this association is lacking in the case of C. compressus. Cataglyphis ants which occupy stress-characterized niches appear to be pre-adapted to tolerate heavy metal pollution. Higher concentrations of Zn and Mn in Ct. longipedem may contribute to the strengthening of the cuticular structures, necessary for nest excavation in the hard, arid soil and for single load carrying. C. compressus ants appear to be pollution sensitive. Their higher Fe content may be related to metal uptake via plant-derived liquids and species-specific regulatory mechanisms. The metal pollution index and biota-to-soil accumulation factors, calculated by using the ant body metal content of the two species, indicate an overall decrease of soil heavy metal concentrations with increase of the site age, which reflects the degree of pollution related to the mine site age. The concentrations of total and available heavy metals (Fe, Zn, Mn, Pb, and Cu) were significantly lower in the ant nest debris soil as compared to the reference soil. The results of the present study highlight the role of ants as bioindicators and in bioremediation of contaminated soil.

Symbiont-mediated shifts in sandprawn behaviour: Implications for ecosystem functioning in marine soft-sediment ecosystems

Ecosystem engineering by burrowing species is one of the most influential determinants of community structure in marine sedimentary ecosystems. However, per capita ecosystem engineering rates displayed by burrowers are variable, and thereby contribute to enhancing local biotic and abiotic variability. Lacking in current understanding of processes influencing variability in ecosystem engineering rates by burrowers and consequent feedbacks to assemblages are interactions occurring between burrowers and their burrow-symbionts. In this paper, we quantify behavioural responses of burrowing sandprawns (Callichirus kraussi: Crustacea: Axiidea) to burrow symbionts (Betaeus jucundus: Crustacea: Alpheidae) using controlled laboratory experiments. We demonstrate that sandprawns display discrete behaviours in response to B. jucundus with distinct levels of tolerance. Such variability in tolerances of sandprawns to B. jucundus is consistent with the idea that the outcomes of symbiotic relationships are variable, depending on processes that shift the costs and benefits involved for partners. Importantly, these discrete tolerances were associated with significant changes to time spent by sandprawns on ecosystem engineering activities (sediment turnover, burrow irrigation) with intolerant sandprawns increasing sediment turnover rate by 50% and decreasing irrigation by 30%. In a second experiment seeking to determine if variability in sandprawn responses to B. jucundus could be due to differences in sandprawn sexes, we demonstrate that male and female sandprawns respond differently to the presence of B. jucundus, with differences in time spent on ecosystem engineering in the presence of B. jucundus. Taken collectively, our results highlight the complex behaviours occurring within burrows in marine sediments and their potential to influence ecosystem activities of burrowers.

How effective are disturbance – tolerant, agroecosystem – nesting ant species in improving soil fertility and crop yield?

Study of the abundance, diversity and nest densities of agroecosystem-inhabiting ant species, in fallow, freshly tilled and cultivated farmers’ fields revealed that Pheidole latinoda had highest abundance, nest density and disturbance-tolerance ability. Thirty-one arthropod morphospecies belonging to 12 orders were recorded in the nest entrance rim debris piles of this ant species. Hence, P. latinoda was selected to study the impact of nest rim debris soil on soil fertility and yield of two common crops, rice and tomato, widely cultivated in the Indo-Gangetic plains of India. Experimental field studies revealed that ant-related enrichment results in significant increase of the C, N and P contents of the bulk soil and a doubling of the soil microbial biomass. The soil enrichment significantly enhanced the yield of both the crop plants in a dose-dependent manner. A significant positive correlation was found between the ecophysiological traits including the specific leaf area, plant height and total plant weight of both rice and tomato plants, and the soil chemical constituents i.e. total C, N, P, NH4-N, NO3-N, microbial biomass C, N and P. The ecosystem engineering activities of P. latinoda ant colonies apparently enriched the soil via the nutrient cycling activities of the debris arthropods, on the externally discarded organic refuse. Since P. latinoda increases productivity via increase in soil fertility and also has the potential to suppress insect pests of crops, conservation of such ant species could enhance agricultural sustainability, through multiple pathways.

Where do eusocial insects fit into soil food webs?

Social insects are an obvious example of soil macrofauna whose role in soil food webs remains poorly understood. Termites and ants are among the most abundant invertebrates found in many terrestrial ecosystems. Termites are functionally detritivores while ants are functionally omnivores in most soil food webs although variation in ant feeding habits and preferences can mean that some species are functionally herbivores while others are predators. The areal abundance of termites and ants in soils, their ecosystem engineering activities in soils and dead wood, and their enormous variety of species interactions with soil organisms suggest that they are key members of soil food webs. Identifying the species of social insects present in soil food webs and quantifying their abundance by collecting whole colonies, whenever possible, will allow quantification of their areal abundance. Using manipulative experiments to test their impacts in combination with studying their areal abundance, diet, and describing the interacting species found within their functional domains (nests, galleries, gut faunae, etc.) it will be possible to better understand the impacts of social insects on soil food webs.

Facilitation in the low intertidal: effects of an invasive species on the structure of an estuarine macrozoobenthic assemblage

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 522:157-167 (2015) - DOI: https://doi.org/10.3354/meps11168 Facilitation in the low intertidal: effects of an invasive species on the structure of an estuarine macrozoobenthic assemblage Adriana Novais1,*, Allan T. Souza2, Martina Ilarri3, Cláudia Pascoal1, Ronaldo Sousa1,2 1CBMA - Centre of Molecular and Environmental Biology, Department of Biology, University of Minho, Campos de Gualtar, 4710-057 Braga, Portugal 2Interdisciplinary Centre of Marine and Environmental Research (CIIMAR/CIMAR), University of Porto, Rua dos Bragas 289, 4050-123 Porto, Portugal 3ICBAS-UP – Abel Salazar Biomedical Sciences Institute, University of Porto, Rua de Jorge Viterbo Ferreira, 228, 4050-313, Porto, Portugal *Corresponding author: adriana.novais1990@gmail.com ABSTRACT: The Asian clam Corbicula fluminea (Müller, 1774) has been recognized as one of the most important invasive alien species in aquatic ecosystems and may have significant ecological and economic impacts. Recently, the presence of C. fluminea was associated with changes in benthic and epibenthic fauna. In this study, we aimed to understand the mechanisms underlying the effects of C. fluminea on an estuarine macrozoobenthic assemblage using a manipulative experiment. We used 5 different treatments (control, rock, closed, live, open), which were placed in a low sandy intertidal soft bottom area in the Minho estuary (NW Iberian Peninsula) for 2 months. We found that the presence of live and open empty shells of C. fluminea had positive effects on the density, biomass and species richness of macrozoobenthos, specifically on species belonging to Annelida, Mollusca and Crustacea. Our results may be explained by 2 main mechanisms: (1) the production of feces and pseudofeces by C. fluminea, which increases organic matter content and food resources for some macrozoobenthic species; and (2) ecosystem engineering activities by C. fluminea, which can create conditions for the establishment of other species via shell production and bioturbation in the sediments. KEY WORDS: Corbicula fluminea · Alien species · Ecosystem engineering · Invertebrates · Minho estuary Full text in pdf format PreviousNextCite this article as: Novais A, Souza AT, Ilarri M, Pascoal C, Sousa R (2015) Facilitation in the low intertidal: effects of an invasive species on the structure of an estuarine macrozoobenthic assemblage. Mar Ecol Prog Ser 522:157-167. https://doi.org/10.3354/meps11168 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 522. Online publication date: March 02, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Impact of typhoon disturbance on the diversity of key ecosystem engineers in a monoculture mangrove forest plantation, Can Gio Biosphere Reserve, Vietnam

Mangrove crabs as key ecosystem engineers may play an important role in the recovery process of storm-damaged forests. Yet, their response to storm disturbance is largely unknown. Here we compare the ground-dwelling brachyuran crab community of intact mangrove stands with that of typhoon gaps having experienced 100% tree mortality. Field work was conducted in two adjacent areas in Can Gio Biosphere Reserve, southern Vietnam. In each area, an 18–20yr old monoculture Rhizophora apiculata stand served as control and was compared with typhoon gaps where downed stems had been removed or left on-site. The gaps were 14 and 20months old when studied in the dry and rainy season 2008, respectively. Time-based sampling of ground-dwelling crabs with hand or shovel was conducted by 4 persons inside 100m2 plots for 30min (7 replicate plots per area, treatment and month). Abiotic (sediment pH, salinity, temperature, grain size, water content, carbon and nitrogen content), and biotic measures (e.g. canopy coverage, woody debris, number of trees, leaf litter) were also taken. Despite complete canopy loss, total crab abundance has not changed significantly (in contrast to biomass) and all 12 species found in the forest were also found in the gaps, demonstrating their robustness. Another 9 gap-exclusive species were recorded and average species number and Shannon diversity were thus higher in the gaps. Perisesarma eumolpe was the most abundant species, both in the forest and in the gaps, and a shift from sesarmids (typical forest species) to ocypodids (generally more prominent in open areas) has not occurred. The persistence of litter-feeding sesarmid crabs prior to the re-establishment of a mangrove canopy is likely to depend on the availability of woody debris on the ground of the gaps, fuelling a mangrove detritus based food web, rather than one based on microphytobenthos and deposit-feeding ocypodids. The presence of burrowing crabs in the gaps suggests that important ecosystem engineering activities are still performed. However, bioturbation may be reduced as crab biomass and body size were smaller in the gaps. Follow-up assessments and field experiments are needed to understand the crabs' role in processing the woody debris, their long-term community dynamics and possible feed-backs between species shifts and gap regeneration.

Is earthworms' dispersal facilitated by the ecosystem engineering activities of conspecifics?

In this work, we documented the influence of earthworm's galleries on their speed of movements during dispersal events in the soil. We quantified, by using X-rays, the dispersal behaviour of earthworms in the soil. The observations were conducted in mesocosms in controlled conditions for 12 h. Our experiments revealed that during a dispersal sequence of a batch of individuals of the species Aporrectodea terrestris (Savigny 1826): (a) individuals used preferentially existing conspecifics' galleries, (b) individual velocity increased after each dispersal event and (c) the lag time before each dispersal event did not seem to be influenced by previous dispersers. Therefore, dispersal seems to be facilitated by conspecifics' activity, which strongly supports the hypothesis of a feedback between ecosystem engineers' activity and their dispersal speed.

The effect of sewage discharge on the ecosystem engineering activities of two East African fiddler crab species: Consequences for mangrove ecosystem functioning

A number of studies have suggested that mangrove forests and their faunal components may be pre-adapted to the impact of organic waste discharge, making them possible natural wastewater treatment wetlands. However, the results from recent research are contradictory. Some studies have shown that negative effects, sometimes subtle and difficult to observe, can be detected on specific biotic components of forests subjected to organic pollution. Therefore, the aim of the present study was to investigate possible alterations in the ecosystem engineering activities of a fiddler crab community dominating the landward belts of Kenyan mangrove forests. The total processed sediment produced by burrowing and foraging activities in a population from a peri-urban mangrove area receiving untreated domestic sewage was compared with that from a forest not affected by urban wastewater. The results showed how the peri-urban site hosted a higher biomass of crabs, which produced a significantly lower amount of processed sediment compared with the pristine site, resulting in a lower total top sediment mixing activity of the crabs. Thus, the present study showed a link between sewage exposure and top sediment reworking by crabs, which is potentially beneficial for mangrove growth and ecosystem functioning. This represents a possible example of cryptic ecological degradation in mangal systems.

Spatial and temporal variation in the effects of fish and crayfish on benthic communities during stream drying

AbstractOmnivorous central stonerollers (Campostoma anomalum) and crayfish (Orconectes meeki meeki) inhabit streams in the Boston Mountain ecoregion of Arkansas, USA, and can have substantial effects on stream ecosystem structure and function through foraging and ecosystem engineering activities. Seasonal summer drying is extensive in these systems and might alter interactions between these consumers and stream benthic communities. Electrical exclusion of consumers was used to examine changes in the effects of fish and crayfish on algal abundance, sediment deposition, sediment organic matter content (as ash-free dry mass [AFDM]), and invertebrate density on tiles during stream drying. Replicate paired exclusion/exposed treatments were placed in 8 pools for two 30-d periods in June and August 2006 during an extended period of stream drying. Consumer exclusion increased algal chlorophyll a 1.5×, sediment organic matter content 2.3×, sediment dry mass 3.4×, and chironomid density 21× relative to levels on ex...

Removal of palm fruits and ecosystem engineering in palm stands by white-lipped peccaries (Tayassu pecari) and other frugivores in an isolated Atlantic Forest fragment

Long-term studies in a 2,178 ha fragment of semideciduous Atlantic Forest demonstrated important interactions between white-lipped peccaries (Tayassu pecari) and the common palms, Syagrus romanzoffiana and Euterpe edulis. We conducted fruit removal and medium-to-large-sized mammalian exclusion experiments to: (1) quantify seasonal fruit consumption from high-density patches beneath parent trees by T. pecari and other consumers, and (2) measure impacts of T. pecari rooting and foraging activities on seedling dynamics in E. edulis stands. A diverse array of fauna consumed S. romanzoffiana fruits. During the dry season, when S. romanzoffiana palms provided 68% of fruit dry weight in the fragment, T. pecari consumed significantly greater amounts than other consumers, and along with Pecari tajacu and Tapirus terrestris, were potential seed dispersers. The rodents, Sciurus ingrami and Agouti paca, consumed most S. romanzoffiana fruits in the wet season, acting as both seed dispersers and predators. More than 95% of E. edulis fruit removal was due to seed predation by T. pecari. Intense removal during the dry season was closely linked with previously documented range shifts and habitat preferences by T. pecari. Exclusion plot experiments in E. edulis (palmito) stands showed that the number and proportion of nonpalmito (not E. edulis) seedlings increased dramatically in the absence of T. pecari rooting and foraging activities that disturbed soil and thinned seedlings. We discuss the importance of these ecosystem engineering activities and palm-peccary trophic interactions for long-term maintenance of E. edulis stands and T. pecari populations, as well as water balance, in the forest fragment.

Nutrient cycling efficiency explains the long‐term effect of ecosystem engineers on primary production

1. Soil organisms, such as earthworms, accelerate mineralization of soil organic matter and are thought to be beneficial for plant growth. This has been shown in short-term microcosm experiments. It is thus legitimate to ask whether these increases in plant growth are due to brief pulses of mineralization or whether these increases are long-lasting. 2. This question was addressed using a system of differential equations modelling the effects of decomposers on nutrient cycling via trophic (nutrient assimilation) and nontrophic effects (through their ecosystem engineering activities). 3. The analytical study of this model showed that these processes increase primary production in the long term when they recycle nutrients efficiently, allowing a small fraction of the recycled nutrients to be leached out of the ecosystem. 4. Mineralization by the ecosystem engineering activities of decomposers seems to deprive them of a resource. However, it was shown that a decomposer may increase its own biomass, through its ecosystem engineering activities, provided the created recycling loop is efficient enough. 5. Mechanisms through which earthworms may modify the efficiency of nutrient cycling are discussed. The necessity of measuring the effect of earthworms on the nutrient input-output balance of ecosystems under field conditions is emphasized.