Small-scale Habitat Heterogeneity Research Articles

The effect of small-scale habitat features on groundfish density in deep-sea soft-bottom ecosystems

In the deep-sea, cold-water corals (CWCs) and other structure-forming fauna locally increase habitat complexity and are host to many fish species. While many studies have focused on hard-bottom CWCs, very little is known about fish associations with soft-bottom CWC habitats. To understand the small-scale linkages between fish, benthic and non-bio-structural habitats in a soft-sediment deep-sea environment, we analysed remotely operated vehicle (ROV) survey videos and recorded the occurrence of fish, invertebrate habitat-forming species and substratum along transects, in the Laurentian Channel Marine Protected Area (MPA) in the Canadian Northwest Atlantic. Almost 13,300 individual fish were recorded, of which all but 65 specimens were identified to family or lower taxonomic rank. The five numerically dominant fish taxa were Redfish (Sebastes spp.), Witch Flounder (Glyptocephalus cynoglossus), Marlin-Spike Grenadier (Nezumia bairdii), Longfin Hake (Phycis chesteri) and one Teleostei morphotype. Teleostei sp1 represents three fish genera (Sandlance (Ammodytes spp.) and two Barracudinas (Arctozenus sp. and Paralepis spp.)) morphologically difficult to differentiate on video footage. Multivariate analysis revealed four habitats based on epibenthic invertebrate densities and diversity. These were dominated by various combinations of sea anemones (Actiniaria), nephtheid soft coral, solitary cup corals (Scleractinia) and three taxa of sea pen (Pennatula spp., Kophobelemnon sp. and Anthoptilum spp.). Univariate analyses performed on dominant fish densities revealed the local influence of hard-bottom substrates and the common influence of soft-sediment micro-features for three fish taxa. All fish densities were correlated with invertebrate density, negatively for Redfish and positively for all other taxa. Our models also predicted the association of four fish taxa with one to two benthic habitats within their preferred depth range. Our results suggest that small-scale habitat heterogeneity in a low relief soft-sediment environment, provided by both physical and biological structures, has a measurable species-specific influence on fish communities. This influence was weaker than typical fish-habitat relationships found in hard-bottom systems, suggesting fish-invertebrate relationships are not obligate. Additionally, we provided evidence that Redfish continue occupying sea pen habitats months after spawning. Our study supports the necessity to continue monitoring the MPA using in-situ video systems to understand the links between fish and habitats in the Laurentian Channel.

Bird response to forest disturbance size in mountain spruce forests in Central Europe

Although natural disturbances are likely to occur more frequently and be more severe in future as a result of climate change, we have little evidence concerning the effect of disturbance size and severity on species diversity. We aimed to compare effects of varying size and severity of natural disturbances on bird species composition in the non-intervention area of Šumava National Park, Czech Republic. For this purpose, we surveyed bird communities in 1) small- and 2) large-scale disturbance, 3) enclaves of live trees in large-scale disturbance areas, and 4) non-disturbed forests. Furthermore, we used habitat characteristics to identify structural factors affecting species composition of bird communities. Birds were sampled by the point count method during the 2021 breeding season and analysed using linear models. Additionally, we use principal component analysis (PCA) to characterize four defined disturbance classes using habitat characteristics. The most important habitat characteristics for bird communities are structural complexity, live tree density, and understorey cover. Small-scale disturbances increased structural complexity of a forest and had a generally positive effect on birds. Both small- and large-scale disturbances supported species nesting on the ground and shrub layer. In contrast, large-scale disturbances negatively affected canopy nesting and specialist species. This likely was due to a reduction of small-scale habitat heterogeneity with increasing disturbance severity. High-severity disturbance changes structurally rich forests to rather uniform, open-canopy habitats that are temporally unsuitable for closed-canopy birds. On the other hand, low-severity disturbance enhances large-scale habitat heterogeneity and maintains suitable habitat for species of closed-canopy forest, including some specialist species.

Leaf turgor loss point shapes local and regional distributions of evergreen but not deciduous tropical trees.

Summary The effects of climate change on tropical forests will depend on how diverse tropical tree species respond to drought. Current distributions of evergreen and deciduous tree species across local and regional moisture gradients reflect their ability to tolerate drought stress, and might be explained by functional traits.We measured leaf water potential at turgor loss (i.e. ‘wilting point’; πtlp), wood density (WD) and leaf mass per area (LMA) on 50 of the most abundant tree species in central Panama. We then tested their ability to explain distributions of evergreen and deciduous species within a 50 ha plot on Barro Colorado Island and across a 70 km rainfall gradient spanning the Isthmus of Panama.Among evergreen trees, species with lower πtlp were associated with drier habitats, with πtlp explaining 28% and 32% of habitat association on local and regional scales, respectively, greatly exceeding the predictive power of WD and LMA. In contrast, πtlp did not predict habitat associations among deciduous species.Across spatial scales, πtlp is a useful indicator of habitat preference for tropical tree species that retain their leaves during periods of water stress, and holds the potential to predict vegetation responses to climate change.

Bison Increase the Growth and Reproduction of Forbs in Tallgrass Prairie

Abstract Grazers may increase grassland plant species diversity through mechanisms such as selective consumption of graminoids resulting in release from competition in subordinate forb species, or the enhancement of small-scale habitat heterogeneity. This study tested the hypothesis bison on tallgrass prairie reduce local plant competition and increase the growth, reproduction, abundance, and diversity of forbs. In addition, because grazers, fire, and other drivers result in high spatio-temporal variation in limiting plant resources in tallgrass prairie, we tested the hypothesis that prairie forbs show high phenotypic plasticity in life history traits in response to large grazers. The growth, reproduction, biomass allocation, and abundances of six common perennial forb species, and estimates of local neighborhood and physical environmental factors were compared in replicate tallgrass prairie sites with and without bison. Greater light availability and percent bare ground; and lower grass canopy density, h...

Effects of topography and land use on woody plant species composition and beta diversity in an arid Trans-Himalayan landscape, Nepal

Distribution patterns of plant species are believed to be impacted by small-scale habitat heterogeneity. However, there have been few comparative studies examining how woody vegetation composition and diversity varies with aspects of different orientations in the Trans-Himalayan region at a local scale. Here, we examined the effects of incoming solar radiation on variation in woody species composition and compared the diversity between the northeast- and southwest-facing slopes in a Trans-Himalayan valley of Nepal. We also examined the implicit interactions between slope orientation and land use in determining the compositional variations between the slopes. We selected two pairs of northeast- and southwest-facing slopes where the first pair has a similar land use and differs in exposure only (Pisang site) while the other pair has clear differences in land use in addition to slope exposure (Braka site). In each site, we sampled 72 plots (36 on each slope) in which the presence and absence of woody species, environmental variables, and disturbance were recorded. Correspondence Analysis (CA) results suggested that the woody species composition significantly varied between northeast- and southwest-facing slopes at both sites, and was significantly correlated with measured environmental variables such as radiation index, altitude, and canopy openness. In the Braka site, mean alpha diversity was significantly higher on southwest-facing slopes. In contrast, beta diversity and gamma diversity were greater on northeast-facing slopes at both sites. Our results suggest that topographic variables (e.g., radiation index) affect species composition between the slopes, likely due to their influence on small scale abiotic environmental variables. However, the effects of land use, such as livestock browsing/grazing may interact with the effects of slope exposure, effectively reducing differences in species composition within slopes but enhancing the differences in beta diversity between contrasting slopes in the Braka. We conclude that slope orientation and land use are important factors in structuring the woody species composition and diversity in the arid Trans-Himalayan region. We suggest that both environmental and land use variables should be taken into consideration in future studies on plant community structure along the cultural landscapes.

Underdispersion and overdispersion of traits in terrestrial snail communities on islands.

Understanding and disentangling different processes underlying the assembly and diversity of communities remains a key challenge in ecology. Species can assemble into communities either randomly or due to deterministic processes. Deterministic assembly leads to species being more similar (underdispersed) or more different (overdispersed) in certain traits than would be expected by chance. However, the relative importance of those processes is not well understood for many organisms, including terrestrial invertebrates. Based on knowledge of a broad range of species traits, we tested for the presence of trait underdispersion (indicating dispersal or environmental filtering) and trait overdispersion (indicating niche partitioning) and their relative importance in explaining land snail community composition on lake islands. The analysis of community assembly was performed using a functional diversity index (Rao's quadratic entropy) in combination with a null model approach. Regression analysis with the effect sizes of the assembly tests and environmental variables gave information on the strength of under- and overdispersion along environmental gradients. Additionally, we examined the link between community weighted mean trait values and environmental variables using a CWM-RDA. We found both trait underdispersion and trait overdispersion, but underdispersion (eight traits) was more frequently detected than overdispersion (two traits). Underdispersion was related to four environmental variables (tree cover, habitat diversity, productivity of ground vegetation, and location on an esker ridge). Our results show clear evidence for underdispersion in traits driven by environmental filtering, but no clear evidence for dispersal filtering. We did not find evidence for overdispersion of traits due to diet or body size, but overdispersion in shell shape may indicate niche differentiation between snail species driven by small-scale habitat heterogeneity. The use of species traits enabled us to identify key traits involved in snail community assembly and to detect the simultaneous occurrence of trait underdispersion and overdispersion.

Meiofauna constitute a considerable portion of invertebrate drift among moss-rich patches within a karst hydrosystem

Aiming to establish the most frequent invertebrate taxa in drift at the small spatial scale within a moss-rich karst tufa-precipitating hydrosystem, we sampled drift among microhabitats differing in substratum type and flow conditions along a tufa barrier-cascading lotic reach. Additionally, we addressed the question of the contribution and the potential significance of meiofauna within the overall invertebrate drift at the small spatial scale. During the study period, a total of 60 invertebrate taxa were recorded in the drift. Six of these taxa belonged to the annelid/arthropod meiofauna and they represented 35% of total drift density. Macroinvertebrates found in drift were represented mainly by larval insects. The composition of the most abundant taxa in total drift was as follows: Alona spp. (Cladocera 26.7%), Riolus spp. (Coleoptera: Elmidae 13.2%), Simulium spp. (Diptera: Simuliidae 12.2%), Enchytraeidae (Oligochaeta 10.4%), Hydrachnidia (6.3%), Orthocladinae (Diptera: Chironomidae 3.9%) and Naididae (Oligochaeta 3.6%). Faunal drift densities and amounts of transported particulate matter (PM) were highest at the fast-flowing sites located at the barriers and lowest at the slow- flowing sites within pools. Similarly to the seasonal amounts of transported PM, faunal drift was lowest in winter, and peaked in autumn and in late spring/early summer. Correlation between flow velocity and PM-faunal drift densities suggested a significant effect of the dislodged PM, though a minor influence of discharge and flow velocity on faunal drift. We suggest that the small-scale habitat heterogeneity and the respective feeding and refugial strategies of the fauna, as well as faunal passive dislodgement initiated by the shear forces of the flow were the most important drivers of observed drift patterns.

Effects of habitat quality and hiking trails on the occurrence of Black Grouse (Tetrao tetrix L.) at the northern fringe of alpine distribution in Austria

The Black Grouse (Tetrao tetrix L.), listed in Annex 1 of the European Bird Directive, inhabits the vulnerable alpine treeline ecotone. Reacting sensitively to modifications of the environment, it can be regarded as an indicator species. To assess summer habitat use, we measured habitat parameters and recorded faeces (intestinal droppings) of Black Grouse on a mountain chain of the Northern Limestone Alps at the northern fringe of its distribution. In the area, the existing hiking trails are frequently used by hikers in summer. We modelled summer habitat use and included effects of hiking trails testing three different buffer radii around hiking trails (i.e., 50, 100 and 150 m); the buffer radius of 50 m significantly contributed to the final model of habitat use. Altitude, cover of grasses/herbs, canopy cover of woody plants <5 m, canopy cover of woody plants ≥5 m, grazing intensity, and the interaction term cover of grasses/herbs × canopy cover of woody plants ≥5 m combined with presence–absence of hiking trails best predicted the occurrence of Black Grouse. Our calculations yielded lower probabilities of Black Grouse occurrence areas adjacent to hiking trails (odds of presence reduced by 93 %). Terrestrial mapping of indirect signs and the statistical model were appropriate to depict significant differences of probabilities of occurrence within and outside the buffer zone around hiking trails. Considering the habitat variables in the model, enhancing small-scale habitat heterogeneity seems to be a recommendable habitat management strategy; by creating a fine mosaic of higher woody plants, dwarf shrubs and open, grassy habitat patches, a rich supply of food and cover can be provided within short distances.

Testing heterogeneity–diversity relationships in tropical forest restoration

Restoring small-scale habitat heterogeneity in highly diverse systems, like tropical forests, is a conservation challenge and offers an excellent opportunity to test factors affecting community assembly. We investigated whether (1) the applied nucleation restoration strategy (planting tree islands) resulted in higher habitat heterogeneity than more homogeneous forest restoration approaches, (2) increased heterogeneity resulted in more diverse tree recruitment, and (3) the mean or coefficient of variation of habitat variables best explained tree recruitment. We measured soil nutrients, overstory and understory vegetation structure, and tree recruitment at six sites with three 5- to 7-year-old restoration treatments: control (no planting), planted tree islands, and conventional, mixed-species tree plantations. Canopy openness and soil base saturation were more variable in island treatments than in controls and plantations, whereas most soil nutrients had similar coefficients of variation across treatments, and bare ground was more variable in control plots. Seedling and sapling species density were equivalent in plantations and islands, and were substantially higher than in controls. Species spatial turnover, diversity, and richness were similar in island and plantation treatments. Mean canopy openness, rather than heterogeneity, explained the largest proportion of variance in species density. Our results show that, whereas canopy openness and soil base saturation are more heterogeneous with the applied nucleation restoration strategy, this pattern does not translate into greater tree diversity. The lack of a heterogeneity-diversity relationship is likely due to the fact that recruits respond more strongly to mean resource gradients than variability at this early stage in succession, and that seed dispersal limitation likely reduces the available species pool. Results show that planting tree islands facilitates tree recruitment to a similar degree as intensive plantation-style restoration strategies.

Further evidence for the effect of particle-size diversity on deep-sea benthic biodiversity

The positive correlation between sediment particle-size diversity (a measure of habitat heterogeneity) and deep-sea macrofaunal diversity was first demonstrated two decades ago. The causality of this relationship was not elucidated because of the potential influence of macrofauna on sediment granulometry. Here we test the generality of this correlation using smaller organisms with limited mobility and limited ability to change the physical structure of sediments. Results of partial regressions accounting for the effect of water depth and food availability showed that nematode species and genus diversity were positively correlated with sediment particle-size diversity on the continental slope of New Zealand. Trophic diversity was not correlated with sediment particle-size diversity, however, which could suggest that the relationship between habitat heterogeneity and diversity was not the result of food partitioning between species/genera. Our findings provide support for the importance of small-scale habitat heterogeneity in the maintenance of local diversity in the deep sea, one of the few known environmental factors that may directly influence species co-existence in this biome.

Comparative Feeding Ecology of Two Communities of Chimpanzees (Pan troglodytes) in Kibale National Park, Uganda

Several recent studies have documented considerable intraspecific and intrapopulation ecological variation in primates. However, we generally lack an understanding of how such variability may be linked to concomitant demographic variation among groups or populations of the same species, particularly in regard to large-bodied and wide-ranging species with high ecological flexibility, such as chimpanzees (Pan troglodytes). We compared the feeding ecology of chimpanzees inhabiting 2 sites in Kibale National Park, Uganda that differ 3-fold in chimpanzee density and support notably different plant communities. Chimpanzees at Ngogo, a site with the largest known chimpanzee community and unusually high chimpanzee density, spent a significantly lower percentage of time resting (and pregnant and lactating females spent more time feeding), incorporated higher percentages of ripe fruit in their diet, had lower dietary diversity values, and had shorter and less variable average patch residency times than did their counterparts at the nearby Kanyawara site, which supports a relatively low density of chimpanzees. In addition, feeding party size was significantly and positively related to feeding patch size at Ngogo, but not at Kanyawara. Together these findings aid in explaining the noted disparity in chimpanzee community size and density between Ngogo and Kanyawara by suggesting that the diet of Ngogo chimpanzees is of higher overall quality than that of Kanyawara chimpanzees. They also highlight the potentially profound influence of even small-scale habitat heterogeneity on the ecology of primates. Researchers must take such influences into account when attempting to draw conclusions about species- or population-level characteristics.

Foraging habitat selection by breeding Common Kestrels Falco tinnunculus on lowland farmland in England

Capsule Breeding Common Kestrels prefer to forage over recently cut grass than all other habitat types on farmland. Aims To identify foraging habitat and prey of Common Kestrels during the breeding season. Methods We observed seven pairs of Common Kestrels during the breeding season over three years, using fixed vantage point observations. We recorded foraging attempts, and habitat and prey data for where the birds chose to forage. Compositional Analysis was used to establish use of each habitat category relative to that habitat’s availability within the Kestrels’ observed foraging ranges. Results We found that Kestrels select habitats non-randomly, with cut grass (le;5cm, all cut less than two weeks previously) being the most used relative to availability. Prey taken varied with grass height: the ratio of mammals to invertebrates was greater on cut grass (4.36 mammals: 1 invertebrate) than on longer, uncut grass swards (1.73 mammals: 1 invertebrate). Conclusion Our results highlight the importance of areas of long and short grass in close juxtaposition, to provide conditions suitable for prey and access to them, respectively. The creation and maintenance of such small-scale habitat heterogeneity will be the key to maximizing the benefits of English agri-environment schemes for Common Kestrels.

The use of invertebrates to detect small-scale habitat heterogeneity and its application to restoration practices.

Recent conceptual and technological solutions to biodiversity assessment allow large numbers of invertebrate specimens to be processed rapidly and provide researchers and practitioners with a unique tool for characterizing habitats. One application of these advances is the ability to detect and monitor small-scale habitat heterogeneity and so provide a measure of ecosystem restoration. This case study presents a test of the efficacy of using invertebrates to assess and monitor ecological restoration following bush regeneration. Eight contiguous habitat patches within a suburb of northern Sydney, Australia, were selected to represent areas that had undergone different bush regeneration techniques. A nearby and relatively undisturbed area of bushland was also sampled. A total of 57,806 ground-active invertebrate specimens from 35 different orders were collected in pitfall traps. 1,246 ant (Formicidae) specimens were further sorted into 46 ant morphospecies from 20 genera. Analyses of the three taxonomic data sets, including two different data transformations, demonstrated that: (i) invertebrate communities successfully characterized different sites, providing a high degree of differentiation among sites; (ii) ordinations of the sites allowed visual assessment of the impact of each management technique on the habitat relative to undisturbed habitats; and (iii) characterization of sites could be achieved using abundance classes or binary counts of ant morphospecies, representing potential cost and time savings. The project duration was a total of three person weeks and cost less than US$3,000 (1999 prices) to complete. Measurement of invertebrate assemblages will provide a tool for both rapid assessment of management decisions and a means by which to implement adaptive management and restoration.