Habitat Units Research Articles

Formulating conservation targets for biodiversity pattern and process in the Cape Floristic Region, South Africa

The Cape Floristic Region of South Africa is a global biodiversity hotspot. In 1998, a process of conservation planning began in the region that required quantitative targets for biodiversity. We combined new information and previously available data sets on biodiversity pattern and process to formulate targets for five groups of features: 102 broad habitat units (land types); locality records for 364 plant species in the family Proteaceae; locality records for 345 species of reptiles, amphibians and freshwater fish; estimated distributions and densities of 41 species of large and medium-sized mammals; and six types of spatial surrogates for ecological and evolutionary processes. We discuss our approach to formulating quantitative targets in the context of the general role of targets in conservation planning, the inadequacy of commonly used standard targets such as 10% of features or whole regions, and the uncertainties around setting targets for land types. We then describe our reasoning and methods for analysing data and identifying targets for each group of features. Our targets are not theoretical—they have been used to develop a regional conservation plan for which implementation is underway. Our targets are, however, provisional. Like any other conservation targets, they are estimates of the requirements for persistence of a region's biodiversity made within the constraints of limited information. We expect them to be improved in future reviews of appropriate targets for the Cape Floristic Region and elsewhere.

Effectiveness of land classes as surrogates for species in conservation planning for the Cape Floristic Region

Land classes are often used in conservation planning as surrogates for species. The relationship between these surrogates and the distribution of species is usually assumed but rarely tested. Using broad habitat units (BHUs) to represent biodiversity pattern in the Cape Floristic Region, together with point locality data for species (proteas and selected vertebrates), we calculated the effectiveness of BHUs as surrogates for species. Our planning units were grid cells of about 40 km 2, together with boundaries of existing reserves. After assigning conservation targets to BHUs, we derived minimum sets of planning units to meet all targets and calculated irreplaceability values for all units (irreplaceability measures the likelihood of a unit being required to achieve targets). Results showed that BHUs were good surrogates for the majority of protea species, but were not good surrogates for vertebrate species or for a small subset of protea species. These species shared the following characteristics: rarity, limited ranges, Red Data Book status, specialised habitats not defined by BHUs, and distributions driven by historical rather than contemporary ecological factors. We show that targeting land classes and species simultaneously is a viable option and requires only 0.1–0.8% more land (depending on species targets) than targeting land classes alone. We conclude by recommending two different strategies for combining land class and species data in conservation planning, depending on data availability.

The current configuration of protected areas in the Cape Floristic Region, South Africa—reservation bias and representation of biodiversity patterns and processes

The formulation of a strategic plan for the conservation of terrestrial biodiversity in the Cape Floristic Region (CFR; 87,892 km 2) requires an objective and spatially explicit assessment of the representativeness of major habitat categories (surrogates for biodiversity) currently under protection. A GIS layer of statutory and non-statutory conservation areas was used, along with layers of many biological and physical features, to explore the configuration of conserved areas relative to key biological and physical indicators. Three analyses were performed. (1) Recursive partitioning, a classification-tree analysis technique, was used to contrast features of protected areas with non-protected areas. (2) The conservation status of 16 primary and 88 secondary Broad Habitat Units (BHUs; derived on the basis of topography, geology, homogeneous climatic zones, and floristic composition) was assessed in terms of prescribed conservation targets. (3) The extent to which protected areas are able to sustain ecological and evolutionary processes was explored by assessing the extent of spatial components of these processes for all conservation areas. About 20% of the CFR is protected in some form of conservation area, mostly concentrated on sandstone substrates, and areas with high altitude and steep slopes. The reservation bias towards upland areas has seriously constrained representation of biodiversity pattern and processes. Most of the habitat diversity is poorly represented in the current conservation area system with only 9% of the remaining primary BHUs in the lowlands conserved. However, almost 50% of the Mountain Fynbos Complex is conserved (largely exceeding its conservation target). Spatial components of the ecological processes identified are poorly captured by the conservation area network although faunal and floral migration is possible in the uplands due to the strong spatial connectivity of the protected network.

Measuring conservation value at fine and broad scales: implications for a diverse and fragmented region, the Agulhas Plain

This study explores the implications of spatial scale for conservation planning in the Agulhas Plain, South Africa. Regional planning relies on broad-scale data but fine-scale data are usually required for implementation at local level. This study addresses the implications of broad-scale planning for fine-scale implementation. Two original systems of notional reserves were developed for this region using C-plan, a decision support system for systematic conservation planning. The first conservation plan was derived using broad scale data (1:250,000) and consisted of nine broad habitat units (land classes based on topography, geology, and climate), remote sensing mapping of habitat transformation and large planning units defined by 1/16th degree squares (average size 3900 ha). The second system was identified at a finer scale (1:10,000) using 36 vegetation types (mapped in the field), ground survey mapping of habitat transformation and cadastral boundaries as planning units (average size 252 ha). Using classification trees, this study compared reserve-design efficiency (the area required to achieve conservation targets), the spatial patterns of conservation value (the irreplaceability value of planning units), biodiversity features, and habitat transformation at both scales. A similar amount of land was required to meet all conservation targets (identified using minimum set analysis) at the broad and fine scale. There was considerable overlap between the two conservation plans as most of fine-scale conservation targets could be achieved under the broad-scale conservation plan. However, irreplaceability values, which measure the likelihood of selecting planning units for achieving representation targets, were much higher at the fine scale. The use of broad-scale biodiversity features underestimated irreplaceability value at a fine scale in heterogeneous and fragmented portions of the landscape. The implications of moving from broad- to fine-scale conservation planning, as well as their respective benefits are discussed. Maximising biodiversity conservation while minimising cost and resources might be achieved by a combination of broad-scale assessments for relatively homogeneous and untransformed areas and fine-scale ones for heterogeneous and fragmented areas.

Electrofishing Effort Requirements for Assessing Species Richness and Biotic Integrity in Western Oregon Streams

Abstract We examined the sampling effort required in wadeable western Oregon streams at base flow to estimate fish species richness, percent abundance, and biotic integrity when employing three persons and one backpack electrofisher. Reaches were oversampled longitudinally and data were recorded separately for each habitat unit, allowing us to treat each habitat unit separately during data analyses. The median values of species richness from Monte Carlo simulations of the data indicated that a stream reach 40 times its mean wetted width was adequate to estimate 90% of species richness (i.e., all common species) in western Oregon fish assemblages. A reach length of 40 wetted channel widths was also adequate to precisely score an index of biotic integrity developed for western Oregon. However, where 40 channel widths are less than 150 m, we recommend a minimum distance of 150 m to ensure that sufficient numbers of individuals are captured, rare habitats are encountered, and riparian conditions do not fully ...

Predicting abundance from occupancy: a test for an aggregated insect assemblage

Summary 1The ubiquitous, positive abundance‐occupancy relationship is of potential value to conservation and pest management because of the possibility of using it to predict species abundance from occupancy measures.2 He & Gaston (2000a) developed a model, and a parameterization method, for the prediction of abundance from occupancy based on the negative binomial distribution. There are to date few empirical tests of either the estimation method or model. Here we conduct such a test in a field‐based mesocosm experiment using a Drosophilidae assemblage associated with decaying fruit.3With individual (and groups of) fruit as minimum mapping units, abundance estimates derived using the parameterization method of the He‐Gaston model differed significantly from measured values, and were least accurate for the most abundant species.4Substitution of k‐values corrected for species density in the model did not improve abundance predictions significantly. However, substitution of k‐values calculated directly from the negative binomial distribution yielded highly accurate abundance predictions.5Although the distribution of fly species did not deviate significantly from the negative binomial distribution, and the finest possible minimum mapping units were used (individual fruit), the parameterization method in the He‐Gaston model consistently underestimated the abundance of species in the assemblage because individuals were very highly aggregated within fruit.6Because of its potential importance, this model and parameterization method require further exploration at fine scales, commonly represented by individual habitat units, for highly aggregated species. The incorporation of spatially explicit information may provide a means of improving abundance predictions in this regard.

The use of sandstone blocks to test hypotheses about colonization of intertidal boulders

This study tested the hypothesis that regularly-shaped sandstone blocks in intertidal boulder-fields are colonized by mobile macrofauna at a similar rate to colonization of natural boulders. In addition, the sessile component on these plates (three levels of sessile assemblages) and their position in the boulder-field (three different positions relative to other boulders) were varied to test hypotheses about effects of these features on colonization. The epibiota varied among the three sets of plates and the natural boulders at the start of the experiment. The boulders were very rapidly colonized by a suite of mobile animals, particularly chitons, gastropods and echinoderms. Colonization was sparse and patchy to start with, causing great variability among replicates. Nevertheless, it did not differ among any of the treatments, indicating that even at this early stage, colonization did not differ between natural boulders and blocks, nor according to the sessile assemblage, or the proximity of other boulders. By six months, there was little variability among replicates and the assemblages had converged. This indicates that sandstone plates/blocks can form a standardized unit of habitat which can be used to test models about spatial variation in this relatively specialized fauna.

Relationships between trout habitat use and woody debris in two southern New England streams

Abstract – In‐stream habitat was measured and trout density was estimated in Merrick Brook (105 habitat units) and the Tankerhoosen River (135 habitat units), Connecticut to determine relationships between habitat use of brook trout Salvelinus fontinalis and brown trout Salmo trutta and woody debris. In each habitat unit, woody debris was inventoried, and length, width, depth, area, width : depth ratio and undercut bank area were estimated. Trout abundance was estimated by snorkeling. Multiple regression was used to test relationships between trout density and principal components describing habitat unit variables. In Merrick Brook, habitat unit size and shape explained most of the variability in density of brook trout (<130 and ≥130 mm) and brown trout (<150 mm) among habitat units, although principle components describing large woody debris or fine woody debris contributed significantly to variations in density of brook trout (≥130 mm) and brown trout (<150 and ≥150 mm). In the Tankerhoosen River, fine woody debris explained most of the variability in density of brook trout (<130 and ≥130 mm), followed by habitat unit size and shape. Both large woody debris and fine woody debris contributed significantly to variations in density of brown trout (≥150 mm). These results suggest that woody debris is an important component of wild trout habitat above that provided by habitat unit shape and size alone.

Island theory, matrix effects and species richness patterns in habitat fragments

AbstractIsland biogeography theory, created initially to study diversity patterns on islands, is often applied to habitat fragments. A key but largely untested assumption of this application of theory is that landscape matrix species composition is non‐overlapping with that of the islands. We tested this assumption in successional old field patches in a closely mowed matrix, and because our patches are appropriately viewed as sets of contiguous habitat units we studied patterns of species richness per unit area. Previous studies at our site did not find that diversity patterns on patch ‘islands’ conformed to predictions of island biogeography theory. Our results indicate that when matrix species are removed from the patch samples, diversity patterns conform better to theory. We suggest that classical island theory remains an appropriate tool to study diversity patterns in fragmented habitats, but that allowances should be made for spill‐over colonization of ‘islands’ from the ‘sea’.

Why do Foraging Stream Salmonids Move During Summer?

We hypothesize that foraging stream salmonids move during summer because (1) they monitor habitat conditions at a reach scale (100s of m), and (2) dominant fish move when conditions in their present foraging location become sub-optimal relative to conditions at other locations in the reach. To test these ideas, we quantified temporal variation in foraging habitat quality between late spring and early fall in a reach of a small Rocky Mountain brook charr, Salvelinus fontinalis, stream, predicted optimal-foraging fish distributions within the reach, and experimentally manipulated access to foraging sites and measured fish responses. Our results show that high-quality foraging sites were located at certain places in the reach during one period, but at different places during others, consistent with the hypothesis that fish movement is required if dominant fish are to occupy high-quality foraging sites throughout summer. The optimal foraging model was able to predict foraging locations within study pools, but not the exact location of individual fish within the pools or the reach. However, empirical evidence suggests that fish were distributed in order to maximize energy intake at the reach scale. Finally, dominant fish excluded from their preferred foraging location either left the pools (three of six cases), or began to occupy focal points of the next largest fish which, in turn, exited the pool (two of six cases). If habitat selection was occurring only within habitat units, then large fish, when excluded from their preferred locations, would select the next best locations within the pool. Taken together, these results suggest that charr use summertime movements to both monitor habitat conditions at a large spatial scale, and to gain access to optimal foraging locations even as conditions change temporally.

Estimated spatial requirements of the medium- to large-sized mammals, according to broad habitat units, in the Cape Floristic Region, South Africa

Conservation planning in the Cape Floristic Region (CFR) of South Africa, a recognised world plant diversity hotspot, required information on the estimated spatial requirements of selected medium- to large-sized mammals within each of 102 Broad Habitat Units (BHUs) delineated according to key biophysical parameters. Spatial requirement estimates were derived for 19 omnivore and carnivore species, following a review and extrapolation of extant information. The estimates for 23 herbivore species were derived from a simple spreadsheet model based on forage availability estimates and the metabolic requirements of the species in question; this analysis incorporated adaptations of the agriculture-based Large Stock Unit (LSU) or Animal Unit approach. The LSU approach has various shortcomings but given the virtual absence of information on forage availability (quantity, quality and seasonality) for indigenous herbivores in the CFR, it provides the only extant measure of the influence of key biophysical factors on this parameter, especially at a regional scale. The outcomes of the exercise, viz. densities (hectares/animal), are presented here; these should be considered as testable hypotheses and a cautious 'management by hypothesis' approach should be adopted in their use. This information can be used to guide both conservation planning activities and practical conservation management decisions.

Comparison of snorkeling and electrofishing for estimating abundance and size structure of brook trout and brown trout in two southern New England streams

Abundance and size structure of brook trout Salvelinus fontinalis and brown trout Salmo trutta determined by snorkeling were compared with estimates determined by electrofishing depletion in 30 habitat units of two Connecticut streams. Snorkel counts were significantly correlated ( P<0.001) to electrofishing depletion estimates for two length groups of each species, although the strength of correlations varied between species, streams, and length groups of trout. Some regression equations that predicted electrofishing depletion estimates from snorkel counts were significantly improved with the addition of independent variables describing large woody debris. Regression parameters indicated that snorkel counts were underestimated in habitat units that contained substantial amounts of large woody debris. Overall, length–frequency distributions obtained by snorkeling were similar to those obtained by electrofishing. In one case, the frequency of brown trout less than 15 cm determined by snorkeling was slightly overestimated relative to electrofishing, while the frequency of 15.0–22.9 cm brown trout was slightly underestimated by snorkeling relative to electrofishing. These results suggest that snorkel counts may be a reliable alternative to electrofishing depletion for estimating trout abundance and size structure in habitat units of small- to mid-size Connecticut streams. However, the consideration of woody debris variables may significantly improve the predictive ability of electrofishing depletion estimates based on snorkel counts.

Summer movement and growth of juvenile anadromous salmonids in small western Washington streams

Movements of juvenile coho salmon (Oncorhynchus kisutch), cutthroat trout (Oncorhynchus clarki clarki), and steelhead trout (Oncorhynchus mykiss) were studied by observations and recapture of marked individuals in three western Washington streams to test the hypotheses that few fish would move, downstream movement would predominate, movers would be initially smaller and grow slower after movement than residents, and habitat quality would influence movement. Contrary to predictions, from 28 to 60% of marked fish moved at least one habitat unit, and immigration of unmarked fish also indicated considerable movement. Upstream movement predominated but the stream with the step-pool/cascade channel type had fewer upstream movers and greater distances moved downstream. Coho movers were not smaller than nonmovers, as predicted based on assumptions that movement results from competitive exclusion. Habitat units that coho left were smaller and shallower but lower in density than units where coho remained. Thus, movement is a common phenomenon rather than an aberration, and may reflect habitat choice rather than territorial eviction. Moreover, movers grew faster than nonmovers, so the "mobile fraction" of the population was not composed of competitively inferior fish but rather individuals that thrived. The phenomenon of small-scale habitat- and growth-related movements should be considered when planning and interpreting studies of juvenile salmonid ecology in streams.

Potential distributions of the medium- to large-sized mammals in the Cape Floristic Region, based on historical accounts and habitat requirements>

Conservation planning in the Cape Floristic Region, a recognized world plant diversity hotspot, required systematic (i.e. presence/absence) information on the estimated distributions of the medium- to large-sized mammals. A pragmatic approach for obtaining distribution estimates, for the period prior to arrival of European settlers, was employed. Distribution estimates were based on a combination of a literature survey (with emphasis on early texts) and the ecological requirementsof species, and were mapped within each of 102 Broad Habitat Units delineated according to key biophysical parameters. Theestimated distributions of 42 species are provided in the form of maps; these are accompanied by brief notes on historicaland current occurrences. The distributions, which can be used to guide conservation decisions, should be considered as testable hypotheses.

The Influence of Geomorphic Factors and Geographic Region on Large Woody Debris Loading and Fish Habitat in Alaska Coastal Streams

Large woody debris (LWD) and channel data from three Alaska coastal regions with varying geomorphic channel types were analyzed to document regional variability in LWD abundance, define geomorphic characteristics affecting LWD abundance, and identify relationships between LWD abundance and the formation of pools and gravel bars in streams. Large woody debris abundance was significantly lower at the northern edge of the coastal coniferous forest than in Southeast Alaska and was significantly greater in alluvial gravel-bedded channels than in contained boulder–bedrock channels. More pools and gravel bars were formed by LWD in alluvial channels than in contained channels. Pool spacing (the number of channel widths between pools) decreased with increasing LWD abundance (pieces/km) and was significantly influenced by the interaction between LWD abundance and channel width. As channel width increased, pool spacing was more strongly influenced by changes in LWD abundance, but the relative change in pool spacing diminished with increasing LWD load. The percentage of stream area in pools was insensitive to changes in LWD abundance and was best predicted by channel type. The percentage of habitat units with gravel as the dominant substrate was positively related to LWD abundance and negatively related to stream gradient.

Effects of Wood Placement on Movements of Trout and Juvenile Coho Salmon in Natural and Artificial Stream Channels

We monitored the movements of marked juvenile coho salmon Oncorhynchus kisutch, steelhead O. mykiss, and cutthroat trout O. clarki in a stream reach that had been “restored” with placed wood and a reference reach with no wood placement and tracked the growth and movements of individually marked coho salmon among habitats in artificial channels with and without woody debris. Monthly surveys in Shuwah Creek, Washington, indicated that few (0–33%) of the marked trout or coho salmon moved between the restored and reference reaches. However, a rapid decline in both marked and unmarked fish in late fall and the increasing proportion of unmarked fish indicated considerable migration to and from the study reaches. In the artificial channels, fewer fish moved in the simple (with no wood) channel than in the complex (with wood) channel (22% versus 37%), and the mean distance moved was shorter in the complex channel (4.4 versus 6.7 habitat units). In the simple channel, the fish that moved grew faster than those that did not. Movement may facilitate increased growth in stream reaches with little woody debris, and the placement of woody debris may lead to less frequent and shorter movements.

Caribou habitat mapping and fragmentation analysis using Landsat MSS, TM, and GIS data in the North Columbia Mountains, British Columbia, Canada

Fragmentation of critical early winter caribou habitat in the North Columbia Mountains near Mount Revelstoke and Glacier National Parks in British Columbia, Canada, may be occurring as a result of timber harvesting and wildfires. In this research, habitat suitability models derived from Landsat Multispectral Scanner (MSS) imagery for 1975 and Thematic Mapper (TM) imagery for 1997 were developed to represent the landscape for the study area in a past (1975) and more recent condition (1997). A Hybrid Decision Tree (HDT) Classifier was used to combine maximum likelihood decision rules, a brightness differencing technique, and a spatial/contextual rule base. Verified by field samples and aerial photographs, the accuracy of the resulting habitat unit maps was determined to be 91.8% overall in the 1997 TM classification and 89.5% overall in the 1975 MSS classification. Based on a comparative analysis of selected spatial landscape metrics calculated for each time period, changes in the composition and spatial configuration of early winter habitat were quantified. Overall, the amount of suitable winter habitat available in 1997 represented a decrease of approximately 832.88 ha (8.53%) from 1975 levels. In the observed disturbance pattern, early winter habitat patches in 1997 were smaller and more uniform in size than in 1975, as suggested by decreases in mean patch size and patch size coefficient of variation indices. Spatial pattern analysis results indicated a reduction in geometric complexity, interior core area, and mean proximity between 1975 and 1997, while patch density and edge density had increased over time. The interpretation of changes in landscape structure are consistent with those reported in the literature for other regions, and indicate that fragmentation of early winter caribou habitat has occurred in the study area.

Temperate Terrestrial Vertebrate Faunas in North and South America: Interplay of Ecology, Evolution, and Geography with Biodiversity

Abstract: To help identify the factors that govern species richness in biological preserves, we performed a comparative study of terrestrial vertebrate species richness for two analogous montane areas critical for biodiversity conservation: the Greater Yellowstone region of the Rocky Mountains, United States, and the Nahuel Huapi region, Patagonia, around Bariloche, Argentina. We explored the ecological interactions of such factors as latitude, habitat heterogeneity, inferred productivity, geographic context, history of lineage, and history of environment in generating and maintaining species richness. Overall species richness of terrestrial vertebrates was higher in the Yellowstone area, but patterns were not uniform across vertebrate classes. Ectotherms (reptiles and amphibians) were more diverse in the Patagonian site, whereas endotherms (birds and mammals) were more diverse in the Yellowstone site. The higher diversity of Patagonian ectotherms is a result of abnormally high numbers of species within two specialized taxa: frogs and the lizard genus Liolaemus. There were high percentages of endemic species (68% of amphibians, 35% of reptiles, 15% of mammals) and feral, non‐native mammals (19%) in Patagonia. These results imply that (1) biodiversity is generated and maintained by a combination of local phenomena and by continental area and related historical constraints; (2) the relative weight of the various influences may differ for ectotherms ( fit latitudinal and related models) and endotherms ( fit history‐based models); and (3) because larger‐scale processes are so important for the maintenance of natural biological diversity, it is crucial that biological reserves be selected and managed with an understanding of the geographical and geological context of the continents on which they are located. Reserves located on large continents with connections to other continents preserve large numbers of species per given unit of geographic area and protect critical habitat for species such as migrants that require large areas for maintenance of persistent populations. In contrast, reserves located on relatively isolated continents protect a high number of evolutionarily unique species per given unit of geographic area and have a high potential for colonization by exotic species.

Fidelity and Survival of Juvenile Coho Salmon in Response to a Flood

Abstract We compared the movement and spring out-migrant trap capture of 1,038 juvenile coho salmon Oncorhynchus kisutch tagged with passive integrated transponder (PIT) tags among four alcoves, seven backwaters, and six main-channel pool habitats after a 5-year flood. Sampling was conducted in November 1998 before the flood on 21 November and again in December, January, February, and March in selected habitat units. Along with out-migrant trapping during spring 1999, these repeated sampling efforts were used to measure the fidelity of juvenile coho salmon to particular habitat units, the immigration of coho salmon into those habitat units, and out-migration from them. Following the flood, fidelity and out-migrant trap capture were greater for juvenile coho salmon occupying alcoves (50% and 17.0%) than for those occupying backwaters (16% and 6.1%) or main-channel pools (7% and 2.7%). The out-migrant trap capture of juvenile coho salmon that had been PIT-tagged before the flood (16.1%; N = 209) was similar...

Summer movement and growth of juvenile anadromous salmonids in small western Washington streams

Movements of juvenile coho salmon (Oncorhynchus kisutch), cutthroat trout (Oncorhynchus clarki clarki), and steelhead trout (Oncorhynchus mykiss) were studied by observations and recapture of marked individuals in three western Washington streams to test the hypotheses that few fish would move, downstream movement would predominate, movers would be initially smaller and grow slower after movement than residents, and habitat quality would influence movement. Contrary to predictions, from 28 to 60% of marked fish moved at least one habitat unit, and immigration of unmarked fish also indicated considerable movement. Upstream movement predominated but the stream with the step-pool/cascade channel type had fewer upstream movers and greater distances moved downstream. Coho movers were not smaller than nonmovers, as predicted based on assumptions that movement results from competitive exclusion. Habitat units that coho left were smaller and shallower but lower in density than units where coho remained. Thus, movement is a common phenomenon rather than an aberration, and may reflect habitat choice rather than territorial eviction. Moreover, movers grew faster than nonmovers, so the "mobile fraction" of the population was not composed of competitively inferior fish but rather individuals that thrived. The phenomenon of small-scale habitat- and growth-related movements should be considered when planning and interpreting studies of juvenile salmonid ecology in streams.