Jari Ilmonen

Benthic macrocrustacean and insect assemblages in relation to spring habitat characteristics: patterns in abundance and diversity

We studied variation in benthic macrocrustacean and insect assemblages in relation to spring habitat characteristics in six springs located in a single groundwater area in south-west Finland. We defined five habitat types in the studied springs according to water flow and benthic substrate characteristicsminerogenic brooks, organogenic brooks, helocrenes, floating moss carpets and limnocrene pools. Most studied invertebrate orders, as well as individual taxa, showed differences in relative abundances between the habitat types, but the most common taxa occurred in all springs and habitat types. The studied macroinvertebrates were most abundant in the moss carpet sites and least abundant in the pool sites, but the difference was not statistically significant. We did not observe significant differences in mean taxonomic richness per sample between habitat classes. The observed taxonomic richness in pooled samples of habitat classes was highest in moss carpet habitat and lowest in pool habitat, and the rarefied richness estimate was lowest in pool habitat. Benthic macrocrustacean and insect assemblages varied more between habitat types than between individual springs. In an Nonmetric Multidimensional Scaling ordination analysis, spring brook sites were separated from the moss carpet and pool sites, whereas helocrene sites were widely scattered among sites in other habitat classes. The strongest ecological gradients were related to water flow and the presence of minerogenic substrate, separating lentic and lotic habitats. Abundances of moss and coarse detritus accounted for most of the within-class variation. We identified several indicator species for minerogenic and organogenic brooks and for moss carpet and pool habitats, but none for the helocrenes. We found several occurrences of two crenobiont insect species considered threatened in Finland. We suggest that combined studies on macroinvertebrate and bryophyte assemblages would be a powerful approach in assessing the biodiversity of springs.

Environmental heterogeneity and β diversity of stream macroinvertebrate communities at intermediate spatial scales

Abstract. Theory predicts that different components of species diversity should increase with environmental heterogeneity. Our main aim was to examine the relationship between &bgr;-diversity and environmental heterogeneity in a system with high habitat heterogeneity and very small spatial distances between sites. This system allowed us to examine the effect of habitat heterogeneity on &bgr;-diversity in the absence of dispersal limitation. We surveyed 100 riffle sites (10 riffles in each of 10 streams) for benthic macroinvertebrates in a boreal drainage basin. Streams differed in average community composition (based on canonical analysis of principal coordinates) and heterogeneity in community composition (based on test of homogeneity of dispersion). These results were robust regardless of the distance measures used in distance-based multivariate analyses. &bgr;-diversity was not significantly correlated with stream habitat heterogeneity, despite the fact that the latter was quantified by a large set of environmental variables deemed important for species occurrence in our study streams. Thus, we suggest that the relationship between &bgr;-diversity and habitat heterogeneity was masked by individual species–environment responses and mass effects. Thus, the &bgr;-diversity–habitat heterogeneity relationship may not always be significant, a result that may have important consequences for understanding the structure of community patterns. Despite the absence of a significant &bgr;-diversity–habitat heterogeneity relationship, community structure was significantly associated with environmental factors (e.g., moss cover, stream width, velocity) across the streams in distance-based redundancy analysis. This finding suggests that different ways to associate &bgr;-diversity, community structure, and environmental conditions may yield different insights into the structure of biotic communities.

Inferring the effects of potential dispersal routes on the metacommunity structure of stream insects: as the crow flies, as the fish swims or as the fox runs?

1. Metacommunity research relies largely on proxies for inferring the effect of dispersal on local community structure. Overland and watercourse distances have been typically used as such proxies. A good proxy for dispersal should, however, take into account more complex landscape features that can affect an organisms movement and dispersal. The cost distance approach does just that, allowing determining the path of least resistance across a landscape. 2. Here, we examined the distance decay of assemblage similarity within a subarctic stream insect metacommunity. We tested whether overland, watercourse and cumulative cost distances performed differently as correlates of dissimilarity in assemblage composition between sites. We also investigated the effect of body size and dispersal mode on metacommunity organization. 3. We found that dissimilarities in assemblage composition correlated more strongly with environmental than physical distances between sites. Overland and watercourse distances showed similar correlations to assemblage dissimilarity between sites, being sometimes significantly correlated with biological variation of entire insect communities. In metacommunities deconstructed by body size or dispersal mode, contrary to our expectation, passive dispersers showed a slightly stronger correlation than active dispersers to environmental differences between sites, although passive dispersers also showed a stronger correlation than active dispersers to physical distances between sites. The strength of correlation between environmental distance and biological dissimilarity also varied slightly among the body size classes. 4. After controlling for environmental differences between sites, cumulative cost distances were slightly better correlates of biological dissimilarities than overland or watercourse distances between sites. However, quantitative differences in correlation coefficients were small between different physical distances. 5. Although environmental differences typically override physical distances as determinants of the composition of stream insect assemblages, correlations between environmental distances and biological dissimilarities are typically rather weak. This undetermined variation may be attributable to dispersal processes, which may be captured using better proxies for the process. We suggest that further modifying the measurement of cost distances may be a fruitful avenue, especially if complemented by more direct natural history information on insect dispersal behaviour and distances travelled by them.

Responses of spring macroinvertebrate and bryophyte communities to habitat modification: community composition, species richness, and red-listed species

Abstract.  Like all headwater systems, springs have been increasingly modified by multiple land uses, but the effects of these modifications on species diversity and community composition are poorly understood. We assessed the consequences of forestry-related disturbance (mainly draining) on benthic macroinvertebrate and bryophyte diversity and community composition in boreal springs. We used predictive modeling (BEnthic Assessment of SedimenT [BEAST]), indicator species analysis, and descriptive statistics on data from 55 near-pristine reference springs and 20 modified (test) springs spanning 3 ecoregions (hemiboreal to middle boreal) in Finland. Invertebrate and bryophyte communities were relatively similar between the reference and test springs. BEAST identified deviation from the reference condition in 9 and 10 sites based on benthic macroinvertebrates and bryophytes, respectively. These sites were identified mostly as possibly different from reference, with the exception of a few seriously degraded springs with low levels of groundwater flow. Indicator species for both reference-condition and test springs included spring-preferring and ubiquitous taxa. Bryophyte richness was lower in test than in reference springs, but no significant differences were detected for macroinvertebrate richness. Red-listed species were more common in reference than in test springs. Our results suggest that, despite only moderate effects on community composition, anthropogenic disturbance impoverishes spring fauna and flora and causes a decline of spring-preferring red-listed species. Restoration will be necessary to preserve biodiversity in springs, but benign methods should be used to avoid further disturbance to biota, particularly red-listed spring specialists.

Cranefly (Diptera: Tipuloidea) fauna of a boreal mire system in relation to mire trophic status: implications for conservation and bioassessment

Craneflies (Diptera Tipuloidea) are a typical but poorly known insect group in various moist environments, such as mires. The area of natural mires has strongly decreased in Finland, and there is an urgent need to study and describe the fauna of mires and to determine whether different mire categories support different assemblages of craneflies that might have indicator value. Craneflies were studied using Malaise traps in the Kauhaneva mire system in minerotrophic and ombrotrophic sites, the former subdivided into meso- and oligotrophic sites. A total of 29 cranefly species were recorded. Species richness was highest in mesotrophic sites while the number of species was equally low in oligo- and ombrotrophic sites. Phylidorea squalens, Erioptera flavata, Pedicia rivosa and Tricyphona immaculata were identified as indicators for mesotrophic sites, but no indicators were found for oligo- or ombrotrophic sites. No differences between the species composition of minerotrophic (meso- and oligotrophic combined) and ombrotrophic sites were detected, but when three classes of trophic status were compared, a statistical difference was found. Cranefly species richness in Kauhaneva was low compared to pristine spring habitats. Our results imply, that a focus towards conservation and restoration of mire types with high trophic status would benefit also the conservation of cranefly diversity in the boreal ecoregion. Bioassesments and ecological surveys of craneflies should be designed to cover adequately all trophic status classes within a mire, and especially the mire types with highest trophic status. We also review the distribution and ecology of some potentially regionally threatened cranefly species.

Intraguild predation, cannibalism, and microhabitat use in Calopteryx virgo and Somatochlora metallica larvae: a laboratory experiment

Intraguild predation (IGP) and cannibalism among co-occurring lotic odonate species was studied in Central Finland. A laboratory experiment was performed to assess the microhabitat use and cannibalism between intermediate and late instars of Calopteryx virgo larvae and predation by larger Somatochlora metallica larvae on the intermediate C. virgo instars. The experiment was run in small running-water aquaria where the larvae were able to divide their mutual habitat vertically by clinging onto artificial perches or crawling on the bottom. Life span of the small C. virgo larvae and attack rate on them were compared between the cannibalism and IGP treatments. The effect of predation on the activity, habitat use and spatial distribution of the small C. virgo larvae was examined. The IGP rate was 36%. The prey larvae spent the most of their time on the perches, whereas the S. metallica preferred the substrate. The large C.␣virgo larvae did not cannibalise smaller conspecifics. The presence of a predator (S. metallica) had no effect on the habitat use or activity of the prey (C. virgo) larvae. Habitat use differed more between those species than between conspecifics of different size classes of C. virgo. The spatial distribution between S.␣metallica and C. virgo showed a completely random pattern, whereas the two size classes of C. virgo aggregated in the vegetation. Absence of cannibalism and behavioural observations indicate that C. virgo may have a low tendency for intraspecific aggressions.

Does habitat restoration enhance spring biodiversity and ecosystem functions

Degradation of groundwater-dependent ecosystems has raised a need for their restoration, but ecological responses to restoration are largely unknown. We evaluated the effectiveness of spring restoration using data from near-natural, restored, and human-impacted springs, the major impact being degradation of spring hydrology by forest drainage. We used both taxonomic (bryophytes, macroinvertebrates, and leaf-decomposing fungi) and functional (leaf breakdown) measures of restoration success. We expected that by reducing surface water input, restoration will improve spring hydrology and place spring ecosystems in a trajectory towards more natural conditions. Restored springs were thermally more stable than impacted springs and the contribution of surface water was greatly reduced. Bryophytes were more abundant in restored than in impacted springs but did not differ among restored and natural springs. Similarly, macroinvertebrate communities differed between restored and impacted springs whereas no difference was detected between restored and natural sites. Species diversity and functional attributes showed weaker responses to restoration. Our results suggest that restoration enhances spring habitat quality, and the first signs of biodiversity enhancement were also detectable only a few years post-restoration. Restoration clearly bears great promise as a conservation tool for the protection of this valuable component of regional freshwater biodiversity.

Groundwater contamination and land drainage induce divergent responses in boreal spring ecosystems

Degradation of freshwater ecosystems has engendered legislative mandates for the protection and management of surface waters while groundwater-dependent ecosystems (GDEs) have received much less attention. This is so despite biodiversity and functioning of GDEs are currently threatened by several anthropogenic stressors, particularly intensified land use and groundwater contamination. We assessed the impacts of land drainage (increased input of dissolved organic carbon, DOC, from peatland drainage) and impaired groundwater chemical quality (NO3--N enrichment from agricultural or urban land use) on biodiversity and ecosystem functioning in 20 southern Finnish cold-water springs using several taxonomic and functional measures. Groundwater contamination decreased macroinvertebrate and bacterial diversity and altered their community composition. Changes in macroinvertebrate and bacterial communities along the gradient of water-quality impairment were caused by the replacement of native with new taxa rather than by mere disappearance of some of the original taxa. Also species richness of habitat specialist (but not headwater generalist) bryophytes decreased due to impaired groundwater quality. Periphyton accrual rate showed a subsidy-stress response to elevated nitrate concentrations, with peak values at around 2500 μg L-1, while drainage-induced spring water brownification (increased DOC) reduced both periphyton accrual and leaf decomposition rates already at very low concentrations. Our results highlight the underutilized potential of ecosystem-level functional measures in GDE bioassessment as they seem to respond to the first signs of spring ecosystem impairment, at least for the anthropogenic stressors studied by us.

Identifying taxonomic and functional surrogates for spring biodiversity conservation: Biodiversity Surrogates

Surrogate approaches are widely used to estimate overall taxonomic diversity for conservation planning. Surrogate taxa are frequently selected based on rarity or charisma, whereas selection through statistical modeling has been applied rarely. We used boosted-regression-tree models (BRT) fitted to biological data from 165 springs to identify bryophyte and invertebrate surrogates for taxonomic and functional diversity of boreal springs. We focused on these 2 groups because they are well known and abundant in most boreal springs. The best indicators of taxonomic versus functional diversity differed. The bryophyte Bryum weigelii and the chironomid larva Paratrichocladius skirwithensis best indicated taxonomic diversity, whereas the isopod Asellus aquaticus and the chironomid Macropelopia spp. were the best surrogates of functional diversity. In a scoring algorithm for priority-site selection, taxonomic surrogates performed only slightly better than random selection for all spring-dwelling taxa, but they were very effective in representing spring specialists, providing a distinct improvement over random solutions. However, the surrogates for taxonomic diversity represented functional diversity poorly and vice versa. When combined with cross-taxon complementarity analyses, surrogate selection based on statistical modeling provides a promising approach for identifying groundwater-dependent ecosystems of special conservation value, a key requirement of the EU Water Framework Directive.

Changes in spring macroinvertebrate assemblages following catchment-scale restoration: first results

Most springs in Finland have suffered from anthropogenic disturbance, and many have been completely destroyed (RAATIKAINEN 1989). Drainage o f forests and mires for silvicultural purposes has been one of the most important disturbances affecting springs. Springs, often located within a mire, may need restoration the same as mires (AAPALA 2001). So far, scientific knowledge on the responses o f biota to the restoration of spring habitats is lacking.