David M. Harper

Population-Level Metrics of Trophic Structure Based on Stable Isotopes and Their Application to Invasion Ecology

Biological invasions are a significant driver of human-induced global change and many ecosystems sustain sympatric invaders. Interactions occurring among these invaders have important implications for ecosystem structure and functioning, yet they are poorly understood. Here we apply newly developed metrics derived from stable isotope data to provide quantitative measures of trophic diversity within populations or species. We then use these to test the hypothesis that sympatric invaders belonging to the same functional feeding group occupy a smaller isotopic niche than their allopatric counterparts. Two introduced, globally important, benthic omnivores, Louisiana swamp crayfish (Procambarus clarkii) and carp (Cyprinus carpio), are sympatric in Lake Naivasha, Kenya. We applied our metrics to an 8-year data set encompassing the establishment of carp in the lake. We found a strong asymmetric interaction between the two invasive populations, as indicated by inverse correlations between carp abundance and measures of crayfish trophic diversity. Lack of isotopic niche overlap between carp and crayfish in the majority of years indicated a predominantly indirect interaction. We suggest that carp-induced habitat alteration reduced the diversity of crayfish prey, resulting in a reduction in the dietary niche of crayfish. Stable isotopes provide an integrated signal of diet over space and time, offering an appropriate scale for the study of population niches, but few isotope studies have retained the often insightful information revealed by variability among individuals in isotope values. Our population metrics incorporate such variation, are robust to the vagaries of sample size and are a useful additional tool to reveal subtle dietary interactions among species. Although we have demonstrated their applicability specifically using a detailed temporal dataset of species invasion in a lake, they have a wide array of potential ecological applications.

The ecological basis for river management

The Importance of High Flows for Riverine Environments The Ecological Basis for the Management of Water Quality River Management and Mammal Population Fish Stock Assessment Ecological Management for Angling Ecological Master Plan for the Rhine Catchment.

The habitat-scale ecohydraulics of rivers

Abstract This paper establishes the link between ‘functional habitats’ (biologically defined habitat units) and flow ‘biotopes’ (hydraulically defined habitat units) using Froude number. Froude number has been shown to be the hydraulic variable that best describes surface flow type (flow biotope). The approach used was to examine the relationship between functional habitat occurrence and Froude number, with the aim of developing ‘habitat preference curves’. Fifteen of the 16 functional habitats were found to be distributed with Froude number in a non-random fashion (‘woody-debris’ being the only exception). Eight functional habitats were most likely to occur in the lowest Froude number class. These were ‘silt’, ‘roots’, ‘trailing vegetation’, ‘marginal plants’, ‘leaf-litter’, ‘emergent macrophytes’, ‘floating-leaved macrophytes’, and ‘submerged broad-leaved macrophytes’. The remaining habitats occurred at higher Froude numbers, with a gradient of increasing Froude number going from ‘sand’, to ‘gravel’, to ‘moss’ to ‘macroalgae’ to ‘cobbles’ to ‘submerged, fine-leaved macrophytes’. This information can be applied to river rehabilitation projects. Hydraulic variables, such as Froude number, can be manipulated through changes to channel morphology, to maximise habitat heterogeneity and therefore biodiversity.

Use of ‘functional habitats’ to link ecology with morphology and hydrology in river rehabilitation

1. This paper examines the influence of channel morphology and hydraulics on the occurrence and diversity of ‘functional habitats’ (also called ‘meso-habitats’) in semi-natural and physically degraded rivers. 2. The depths and velocities at which each functional habitat is most likely to be found are described using ‘occurrence matrices’. In most cases, each habitat was associated with distinct depth-velocity conditions. 3. The relationship between habitat occurrence, diversity and river degradation was examined. The deviation of a site from its predicted natural summer wetted width was used as an index of physical degradation. Habitat diversity (measured as the Shannon index) was low for sites that were wider than expected for natural conditions. This was independent of the type of physical perturbation causing the width deviation. 4. Two main types of physical perturbation were identified in the degraded river: over-widening and ponding. Over-widened sites were shallow, slow and dominated by silt and emergent macrophyte habitats. Ponded sites were deep, slow and dominated by floating-leaved macrophyte and macroalgal habitats. 5. River reaches of uniform depth had low habitat diversity compared with reaches containing both shallow and deep areas. 6. It is recommended that objective assessment of the type and extent of physical degradation, prior to restoration, should be made by measurement of depth, velocity, width and functional habitat distribution. Changes in channel morphology should then be designed to create the necessary range of depths and widths, and therefore velocities and habitat types, deemed desirable for that river site. Habitats that are over-dominant or rare can be identified and the ‘occurrence matrices’ used to inform decisions about the change in physical conditions needed to enhance or suppress that habitat. 7. The approach is a cost-effective way to link ecology with morphology and hydrology in river channel rehabilitation. Copyright

The aquatic macrophytes of an English lowland river system: assessing response to nutrient enrichment

Assessment of the effects of nutrients in running water upon macrophytes is compounded by the variety of additional environmental factors which influence their growth. Some classification schemes have been effective in detecting eutrophication on a national or regional scale, and also downstream changes in large single catchments. However, in lowland rivers with naturally nutrient-rich geologies, detection of change at smaller spatial scales has been difficult. This study examined the macrophyte community at 44 sites on the river Welland, a small lowland catchment rising below 150 m in Leicestershire, England. The community at 23 of these sites was adequate for further analysis. The data show that the clearest effect on community composition is caused by watercourse size. However, sites below sewage works, even small village works, did show a reduction in Mean Trophic Rank, (MTR – an assesment system introduced into the UK over the last three years using a 10–100 scale based upon scores and cover value of indicator species). Overall there was a slight but significant correlation of MTR with soluble phosphate and nitrate. The effectiveness of the MTR method is limited at full catchment scale by low numbers of the indicator taxa at small upstream sites. Catchment-scale assessment of the plant community is probably best served by more detailed phytosociological analysis and by the further development of the ‘habitat templet’ approach.

Why should the habitat‐level approach underpin holistic river survey and management?

1. The UKs new River Habitat Survey (RHS) is founded upon the assumption that species depend upon habitats and that higher habitat heterogeneity supports higher biodiversity in river channels, riparian zones and floodplains. 2. The paper reviews the evidence for this assumption. Physical habitats—of substrate and velocity conditions—are created by predictable physical forces acting within the river ‘continuum’, modified by colonization and metabolism of biota. Numerous studies have shown that habitats have distinct biotic assemblages. 3. River management has, in the past, generally simplified habitat structure but, in order to mitigate the worst effects and restore damaged rivers, it is necessary to have a sound understanding of this term as it applies to all components of the river system (channel, riparian zone and floodplain). 4. RHS has a nested approach to river channel habitats and at one level, ‘functional habitats’, the link between river processes and river biodiversity has been demonstrated. ‘The functional habitats’ concept is now used in river management for mitigation of engineering channel works and restoration of drought-damaged rivers. 5. Similar nested approaches still need to be developed in the riparian zone and river-influenced floodplain. Sustainable river management needs to come to terms with the dynamic nature of river habitat change as well as to quantify the economic benefits which habitats provide.

The ecological relationships of aquatic plants at Lake Naivasha, Kenya

The distribution and abundance of the aquatic flora of Lake Naivasha has been constrained by two ecosystem-level processes. One is the natural and unpredictable fluctuation of water levels which the lake experiences, resulting in a drawdown zone of several vertical meters. The other is the consequence of herbivory by several alien species, linked with competition between rooted aquatic plants and phytoplankton.The effects of alien introductions in the 1960s and 1970s was to eliminate submerged vegetation from the lake completely by 1982, principally by crayfish herbivory. Vegetation has been progressively returning since 1984 and this return is coincident with a decline in crayfish population density.Concentrations of phytoplankton have progressively increased since 1982 as a result of nutrient increase caused by a decline in water level and papyrus swamp clearance for agriculture. The relationship between high levels of phytoplankton and extensive littoral weed beds is discussed.

Using macroinvertebrate species assemblages to identify river channel habitat units: an application of the functional habitats concept to a large, unpolluted Italian river (River Ticino, northern Italy)

The functional habitat concept was applied to a large Italian river for the first time. The characteristically wide range of hydraulic conditions present in this river (compared to previously-studied small, lowland, English rivers) were expected to be of central importance to biota and, therefore, to habitat definition. TWINSPAN analysis of the invertebrate assemblages sampled in the Ticino river identified five distinct habitats: two habitats in lotic areas (run-riffle and macrophytes in current), two along the river margins (with and without macrophytes) and one in backwater areas. These correspond to five of the functional habitats identified in U.K. lowland rivers. Each of these five functional habitats could be defined either in terms of hydraulics, substratum and/or presence/absence of macrophytes. Representative taxa are presented for each habitat and community structure discussed. Macrophyte and run-riffle habitats supported the most heterogeneous and abundant benthic fauna. No match was found between replicates grouped by invertebrate assemblage (the five functional habitats identified by TWINSPAN) and the grouping of the same replicates by PCA, carried out on the physical data matrix. While obvious velocity differences were found between the functional habitats, of particular note was the fact that the Froude number did not show any clear association with habitat type. In the future, improved river management will follow improved understanding of river habitats.

Medicinal flora and ethnoecological knowledge in the Naran Valley, Western Himalaya, Pakistan.

BackgroundMountain ecosystems all over the world support a high biological diversity and provide home and services to some 12% of the global human population, who use their traditional ecological knowledge to utilise local natural resources. The Himalayas are the worlds youngest, highest and largest mountain range and support a high plant biodiversity. In this remote mountainous region of the Himalaya, people depend upon local plant resources to supply a range of goods and services, including grazing for livestock and medicinal supplies for themselves. Due to their remote location, harsh climate, rough terrain and topography, many areas within this region still remain poorly known for its floristic diversity, plant species distribution and vegetation ecosystem service.MethodsThe Naran valley in the north-western Pakistan is among such valleys and occupies a distinctive geographical location on the edge of the Western Himalaya range, close to the Hindu Kush range to the west and the Karakorum Mountains to the north. It is also located on climatic and geological divides, which further add to its botanical interest. In the present project 120 informants were interviewed at 12 main localities along the 60 km long valley. This paper focuses on assessment of medicinal plant species valued by local communities using their traditional knowledge.ResultsResults revealed that 101 species belonging to 52 families (51.5% of the total plants) were used for 97 prominent therapeutic purposes. The largest number of ailments cured with medicinal plants were associated with the digestive system (32.76% responses) followed by those associated with the respiratory and urinary systems (13.72% and 9.13% respectively). The ailments associated with the blood circulatory and reproductive systems and the skin were 7.37%, 7.04% and 7.03%, respectively. The results also indicate that whole plants were used in 54% of recipes followed by rhizomes (21%), fruits (9.5%) and roots (5.5%).ConclusionOur findings demonstrate the range of ecosystem services that are provided by the vegetation and assess how utilisation of plants will impact on future resource sustainability. The study not only contributes to an improved understanding of traditional ethno-ecological knowledge amongst the peoples of the Western Himalaya but also identifies priorities at species and habitat level for local and regional plant conservation strategies.

A catchment‐scale approach to the physical restoration of lowland UK rivers

1. This paper advocates a catchment-scale perspective for river restoration and for individual rehabilitation works even though, at present, such works are often small-scale and ad hoc in nature. The catchment-scale approach is the logical consequence of the application of fundamental principles of river science to the philosophy of river restoration. 2. The five principles that river restoration should incorporate are: i) the hierarchy of river systems; ii) the proportional relationships between discharge and channel dimensions; iii) the importance of the physical and biological continua of natural rivers; iv) the four-dimensional nature of river systems; and v) the role of heterogeneity in maintaining biodiversity and that of disturbance in maintaining heterogeneity. 3. Two sets of examples are given to illustrate the need for these five principles. One set relates to the role of trees in river processes (and in river restoration), while the other relates to the rehabilitation of physical structures in rivers at a different scale. 4. The value of trees both for the maintenance of water quality and for their conservation value in upper-order rivers is demonstrated. This, combined with evidence elsewhere for trees as an integral part of the river-riparian ecotone, suggests the restoration of lowland headwater streams as being totally tree-influenced. In middle and lower reaches of rivers, it is important to restore the river–floodplain interactions. Continuity with groundwater through the hyporheos as a result of riffle-pool rehabilitation and flood-regeneration of meadows and alluvial forests should be the long-term vision for lower-reach restoration. 5. In the interim, piecemeal rehabilitation of the physical heterogeneity of the bed and banks in large rivers can be locally successful provided that it restores coarse particles and interstices where they are absent through artificial material and/or siltation, but not if it fails to recognize fully the importance of replacing lost heterogeneity. Copyright