An evaluation of camera traps for inventorying large- and medium-sized terrestrial rainforest mammals

Mammal inventories in tropical forests are often difficult to carry out, and many elusive species are missed or only reported from interviews with local people. Camera traps offer a new tool for conducting inventories of large- and medium-sized terrestrial mammals. We evaluated the efficiency of camera traps based on data from two surveys carried out at a single site during 2 consecutive years. The survey efforts were 1440 and 2340 camera days, and 75 and 86% of the 28 large- and medium-sized terrestrial mammal species known to occur at the site were recorded. Capture frequencies for different species were highly correlated between the surveys, and the capture probability for animals that passed in front of the cameras decreased with decreasing size of the species. Camera spacing and total survey area had little influence on the number of species recorded, with survey effort being the main factor determining the number of recorded species. Using a model we demonstrated the exponential increase in survey effort required to record the most elusive species. We evaluated the performance of different species richness estimators on this dataset and found the Jackknife estimators generally to perform best. We give recommendations on how to increase efficiency of camera trap surveys exclusively targeted at species inventories.     

Identifying hotspots of molluscan species richness on rocky intertidal reefs

A significant question faced by environmental managers is how muchsurvey effort is required in order to obtain an accurate representation of thespecies richness in an area. The appropriateness of rapid survey techniques foridentifying biodiverse hotspots has not been previously tested for molluscs onintertidal rocky reefs. We used species inventories from standardized 4-h searchsurveys to rank 13 intertidal reefs in terms of their species richness and thesewere then compared to cumulative species records following repeated surveys fromthe same sites. A total of 172 surveys were conducted during low water springtides over a 3 year period, with up to 20 surveys at a single site.Species richness in the inventories varied from 20 to 94 on the different reefs.There was a strong correlation between the number of species recorded in thestandardized inventory and the total species richness from cumulative surveyrecords (r = 0.969; P < 0.001).Importantly, the total species diversity recorded at each site was not relatedto the number of surveys that were conducted at that site(r = 0.110; P = 0.784). This confirmsthat a single standardized timed search produces a useful representation ofmolluscan species richness. The majority of molluscs recorded in this study wereendemic to Australia (59%) and, significantly, the number of endemics waspositively correlated to the total species richness found at each site(r = 0.992; P < 0.0001). Our dataprovide clear evidence for a local hotspot of molluscan species richness andendemism on the northern side of Bass Point, Shellharbour. We suggest that on alocal scale biodiversity hotspots should only be identified as those sites thatcontain significantly more species than the local average. Two standarddeviations above the mean appears to be an appropriate cut-off for identifyinglocal biodiversity hotspots.     

Estimating bird species richness: How should repeat surveys be organized in time?

Abstract Estimates of species richness for a given area require that repeat surveys be taken, so that the statistical robustness of the estimate can be assessed. But how should these repeat surveys be organized in time? Here we present a case study of Australian woodland birds, surveyed using the ‘active timed area search’ method, which has become the standard unit for the Australian Bird Atlas, a continental‐scale bird survey. To date, there has been no assessment of how estimates of species richness derived from this method are affected by the temporal organization of the repeat surveys. For instance, can conducting the repeat surveys in sequence on the same day effectively capture richness, or will additional species be obtained by repeating the surveys on different days within a season? If so, does the spacing of the repeat visits throughout the season have an effect? To answer these questions, we surveyed woodland birds in the Mount Lofty Ranges, South Australia, during late spring–summer 1999–2000, and compared the performance of two different temporal configurations of repeat visits to sites: (i) six repeat surveys performed on the same day; and (ii) three repeat surveys on different days. For both, we calculated the average number of species actually sighted and also estimated total species richness. The data supported our hypothesis that the same‐day surveys would yield fewer species and underestimate total species richness. The different‐day repeats captured significantly more species per unit of survey effort, and yielded a higher richness estimate. However, the timespan over which different‐day surveys were conducted within a season did not have a significant influence on species richness estimates, evincing a qualitative advantage to surveying on different days, regardless of the spacing of repeat visits. These results may be of assistance to conservation managers when planning cost‐efficient monitoring regimes.     

Long-term bat study on an island in the southeastern Brazilian coast with comparison of richness and composition of species among sites

Although Rio de Janeiro is one of the best sampled states of Brazil for bats, there are still some poorly studied islands on its coast. Hence, we inventoried the bat species of an island on the southwestern coast of Rio de Janeiro, compared five sites sampled within this island, and compared its bat community with seven other sites in the same region. We carried out sampling in July 1995 and from September 2006 to August 2010, comprising 58 samplings. We captured a total of 1502 individuals of 25 bat species with mist nets set far from roosts, or close to or inside roosts. The most abundant species were Artibeus lituratus, Molossus molossus, and Carollia perspicillata. Total sampling effort was 89,400 m² h. The present study was one out of five inventories carried out in the southwestern coast of Rio de Janeiro that registered more than 1000 bat individuals from more than 24 bat species. Long-term inventories on islands are still needed, because they can result in a large number of species and captures as observed in the present study.     

The Diversity and Distribution of the Fruit Bat Fauna (Mammalia, Chiroptera, Megachiroptera) of Danjugan Island, Cauayan, Negros Occidental, Philippines (with Notes on the Microchiroptera)

Bats are the most diverse mammalian order in the Philippines and whilst many endemic and threatened species have been documented, they are also probably the least well-known order. Negros Island (central Visayas, Philippines) represents one of the ten highest-ranking sites globally for megachiropteran diversity, and is listed as a priority area for the establishment of protected areas for megachiropteran conservation. It is also listed as a priority site for survey work. The current study undertook mist-netting, roost and observation surveys of the bat fauna of Danjugan Island, off the west coast of Negros Occidental, to inventory the bat species present and to provide baseline ecological information to identify key areas of conservation concern. Eight species – five megachiropterans and three microchiropterans – were recorded over the course of the study, representing over 10% of the total Philippine bat fauna. Four of the species are new records for the island, and three are IUCN Red Listed. The results show that the island provides important cave- and tree-roosting areas for the local populations of several endemic and globally endangered species and sub-species. Already designated with reserve status, and with an environmental education programme established within the local communities, the island may be considered of national and global importance for bat conservation. Recommendations are given for future management.     

Assessing biodiversity with species accumulation curves; inventories of small reptiles by pit‐trapping in Western Australia

Abstract We examined 11 non‐linear regression models to determine which of them best fitted curvilinear species accumulation curves based on pit‐trapping data for reptiles in a range of heterogeneous and homogenous sites in mesic, semi‐arid and arid regions of Western Australia. A well‐defined plateau in a species accumulation curve is required for any of the models accurately to estimate species richness. Two different measures of effort (pit‐trapping days and number of individuals caught) were used to determine if the measure of effort influenced the choice of the best model(s). We used species accumulation curves to predict species richness, determined the trapping effort required to catch a nominated percentage (e.g. 95%) of the predicted number of species in an area, and examined the relationship between species accumulation curves with diversity and rarity. Species richness, diversity and the proportion of rare species in a community influenced the shape of species accumulation curves. The Beta‐P model provided the best overall fit (highest r²) for heterogeneous and homogeneous sites. For heterogeneous sites, Hill, Rational, Clench, Exponential and Weibull models were the next best. For homogeneous habitats, Hill, Weibull and Chapman–Richards were the next best models. There was very little difference between Beta‐P and Hill models in fitting the data to accumulation curves, although the Hill model generally over‐estimated species richness. Most models worked equally well for both measures of trapping effort. Because the number of individuals caught was influenced by both pit‐trapping effort and the abundance of individuals, both measures of effort must be considered if species accumulation curves are to be used as a planning tool. Trapping effort to catch a nominated percentage of the total predicted species in homogeneous and heterogeneous habitats varied among sites, but even for only 75% of the predicted number of species it was generally much higher than the typical effort currently being used for terrestrial vertebrate fauna surveys in Australia. It was not possible to provide a general indication of the effort required to predict species richness for a site, or to capture a nominated proportion of species at a site, because species accumulation curves are heavily influenced by the characteristics of particular sites.     

A practical sampling design for acoustic surveys of bats

Acoustic surveys are widely used for describing bat occurrence and activity patterns and are increasingly important for addressing concerns for habitat management, wind energy, and disease on bat populations. Designing these surveys presents unique challenges, particularly when a probabilistic sample is required for drawing inference to unsampled areas. Sampling frame errors and other logistical constraints often require survey sites to be dropped from the sample and new sites added. Maintaining spatial balance and representativeness of the sample when these changes are made can be problematic. Spatially balanced sampling designs recently developed to support aquatic surveys along rivers provide solutions to a number of practical challenges faced by bat researchers and allow for sample site additions and deletions, support unequal-probability selection of sites, and provide an approximately unbiased local neighborhood-weighted variance estimator that is efficient for spatially structured populations such as is typical for bats. We implemented a spatially balanced design to survey canyon bat (Parastrellus hesperus) activity along a stream network. The spatially balanced design accommodated typical logistical challenges and yielded a 25% smaller estimated standard error for the mean activity level than the usual simple random sampling estimator. Spatially balanced designs have broad application to bat research and monitoring programs and will improve studies relying on model-based inference (e.g., occupancy models) by providing flexibility and protection against violations of the independence assumption, even if design-based estimators are not used. Our approach is scalable and can be used for pre- and post-construction surveys along wind turbine arrays and for regional monitoring programs. © 2011 The Wildlife Society.     

Determining adequate trapping effort and species richness using species accumulation curves for environmental impact assessments

Abstract Environmental impact assessments (EIA) require that the proponent indicates the potential impact that a development will have on the biodiversity of the area. As part of this assessment it is normal practice to inventory the vertebrate species in the area. We show here how species accumulation curves can be used as a tool by environmental consultants to indicate the adequacy of their trapping effort and predict species richness for a disturbance site. The shape of a species accumulation curve is influenced by the number of species in an assemblage and the proportional number of singletons (rarely caught species) in the survey sample. We provide guidelines for the number of individuals that need to be caught in a trapping program to achieve 80% and 90% of the species in a habitat, and we indicate how this number can be adjusted to accommodate variations in relative species abundance.     

Habitat-associated and temporal patterns of bat activity in a diverse forest landscape of southern New England, USA

The development and use of acoustic recording technology, surveys have revealed the composition, relative levels of activity, and preliminary habitat use of bat communities of various forest locations. However, detailed examinations of acoustic surveys results to investigate temporal patterns of bat activity are rare. Initial active acoustic surveys of bat activity on the Quabbin Reservoir watershed in central Massachusetts recorded high numbers of call sequences by five bat species. The results showed the importance of aquatic and open habitats for bats in this diverse forest landscape. Because the preliminary surveys were restricted in extent (habitats), number (replicates), and duration (active surveys only, limited number of repeated surveys), the authors strongly recommended more comprehensive and extensive surveys of bat activity on the area. This paper reports the results of active (manual) and passive (automated) acoustic bat activity surveys in three replicates of ten habitats, conducted three to four times per year over the course of the study between 2004 and 2006. Over the full study, 2,800 actively-recorded 37,632 passively-recorded call sequences were examined and identified to species when possible. General patterns in activity did not differ by habitat between the two survey methods. Call sequences were recorded more often in open, especially aquatic habitats than in cluttered habitats. The use of passive surveys allowed for the assessment of temporal patterns of activity and an analysis of the relationship between ambient temperature and activity.     

The inventory of bryophytes at sites: completeness and survey effort

Abstract

Knowledge of the species present within a site is often used to inform decisions that have significant implications for biodiversity conservation. This study surveyed eight woodland sites in north-west England for bryophytes. Searches for species within each site continued until all areas had been approached to within a minimum of 50 m and at least 60 minutes had elapsed since the discovery of a new species. Survey data were used to build predictive models that provided an estimate of the total number of species present at each site and the time required to compile a complete inventory. The ‘50 m 60 minutes stopping rule’ consistently produced comprehensive inventories for sites, judging by the numbers of species found and model predictions of the total number of species present. The study suggests that a minor alteration to conventional survey practice and a small amount of data analysis can provide useful assessments of the completeness of bryophyte inventories for sites.     

Species richness and assemblages of bats along a forest elevational transect in Papua New Guinea

Over the past decades, elevational gradients have become a powerful tool with which to understand the underlying cause(s) of biodiversity. The Mt. Wilhelm elevational transect is one such example, having been used to study the birds, insects, and plants of Papua New Guinea (PNG). However, a survey of mammals from this forest elevational transect was lacking. We thus aimed to investigate patterns in the community structure and species richness of bats (Chiroptera) along the transect, link the species to available regional data, and explain the observed patterns by including environmental characteristics. Bat assemblages were surveyed between 200 m and a timberline at 3700 m a.s.l. at eight study sites separated by 500 m in elevation. We conducted mist-netting and acoustic surveys to detect and identify species at each site. Regional data were compiled to compare local with regional diversity. Finally, biotic (i.e., food availability, habitat features) and abiotic (i.e., mean daily temperature) factors were included in our analyses to disentangle the ecological drivers underlying bat diversity. Results revealed that species richness decreases with ascending elevation and was best explained by a corresponding decrease in temperature. We observed both turnover and nestedness of the species composition at regional scale whereas turnover was dominant at local scale. Extensions and shifts of bat elevational ranges were also found in Mt. Wilhelm. Consequently, despite that the study was restricted to one mountain in PNG, it demonstrates how basic inventory surveys can be used to address ecological questions in other similar and undisturbed tropical mountains.     

Rapid Simultaneous Estimation of Aboveground Biomass and Tree Diversity Across Neotropical Forests: A Comparison of Field Inventory Methods

A standardized rapid inventory method providing information on both tree species diversity and aboveground carbon stocks in tropical forests will be an important tool for evaluating efforts to conserve biodiversity and to estimate the carbon emissions that result from deforestation and degradation (REDD). Herein, we contrast five common plot methods differing in shape, size, and effort requirements to estimate tree diversity and aboveground tree biomass (AGB). We simulated the methods across six Neotropical forest sites that represent a broad gradient in forest structure, tree species richness, and floristic composition, and we assessed the relative performance of methods by evaluating the bias and precision of their estimates of AGB and tree diversity. For a given sample of forest area, a ‘several small’ (< 1 ha) sampling strategy led to a smaller coefficient of variation (CV) in the estimate of AGB than a ‘few large’ one. The effort (person‐days) required to achieve an accurate AGB estimate (< 10% CV), however, was greater for the smallest plots (0.1 ha) than for a compromise approach using 0.5 ha modified Gentry plots, which proved to be the most efficient method to estimate AGB across all forest types. Gentry plots were also the most efficient at providing accurate estimates of tree diversity (< 10% CV of Hill number). We recommend the use of the 0.5 ha modified Gentry plot method in future rapid inventories, and we discuss a set of criteria that should inform any choice of inventory method.     

Assessment of sampling approaches for a multi‐taxa invertebrate survey in a South African savanna‐mosaic ecosystem

Invertebrate diversity is seldom included in conservation assessments, primarily because information is lacking. Broad surveys may be too costly, difficult or ineffective. Here we assess a ‘shopping basket’ approach, targeting 17 taxa using a range of methods. We sampled 43 one‐hectare sites stratified within 560 km² of heterogenous African savanna. We achieved up to 80% sampling completeness for epigaeic fauna, but generally much lower completeness (around 50%) for plant‐dwelling and flying taxa. For the former we identified duplication of methods, and for the latter, addition of methods and increased temporal variation rather than effort would improve completeness. Within a taxon, sampling 75% of species present required, on average, about 784 individuals. When considering the local richness, 75% completeness required about 27 individuals per species, but these figures require validation in other areas. About 58 sites were required to achieve 75% sampling completeness, translating to about one site per 10 km². The percentage of species sampled only in a particular month ranged between 4% and 46%, with greater temporal effects recorded for flying taxa than for epigaeic ones. The trend was similar for species unique to a particular year, with the most extreme case being 67% of the butterfly species sampled one year not previously recorded. We demonstrated and evaluated the feasibility of a simultaneous multi‐taxon survey approach to produce data useful for conservation planning and monitoring. We strongly recommend a quantified approach for surveys and inventories, with details such as specific methods decided based on the biome sampled, and taxonomic expertise available for identification.     

Improving geographically extensive acoustic survey designs for modeling species occurrence with imperfect detection and misidentification

Acoustic recording units (ARUs) enable geographically extensive surveys of sensitive and elusive species. However, a hidden cost of using ARU data for modeling species occupancy is that prohibitive amounts of human verification may be required to correct species identifications made from automated software. Bat acoustic studies exemplify this challenge because large volumes of echolocation calls could be recorded and automatically classified to species. The standard occupancy model requires aggregating verified recordings to construct confirmed detection/non‐detection datasets. The multistep data processing workflow is not necessarily transparent nor consistent among studies. We share a workflow diagramming strategy that could provide coherency among practitioners. A false‐positive occupancy model is explored that accounts for misclassification errors and enables potential reduction in the number of confirmed detections. Simulations informed by real data were used to evaluate how much confirmation effort could be reduced without sacrificing site occupancy and detection error estimator bias and precision. We found even under a 50% reduction in total confirmation effort, estimator properties were reasonable for our assumed survey design, species‐specific parameter values, and desired precision. For transferability, a fully documented r package, OCacoustic, for implementing a false‐positive occupancy model is provided. Practitioners can apply OCacoustic to optimize their own study design (required sample sizes, number of visits, and confirmation scenarios) for properly implementing a false‐positive occupancy model with bat or other wildlife acoustic data. Additionally, our work highlights the importance of clearly defining research objectives and data processing strategies at the outset to align the study design with desired statistical inferences.     

Spatially explicit estimation of occupancy,detection probability and survey effort needed to inform conservation planning

Aim It is increasingly recognized the importance of accounting for imperfect detection in species distribution modelling and conservation planning. However, the integration of detectability into a spatially explicit frame has received little attention. We aim (1) to show how to develop distribution maps of both detection probability and survey effort required to reliably determine a species presence/absence and (2) to increase awareness of the spatial variation of detection error inherent in studies of species occurrence. Location North‐western Spain. Methods  We registered the presence/absence of the endangered Egyptian vulture (Neophron percnopterus) in 213 surveys performed in 40 of 104 territories once known to be occupied. We model simultaneously both detection probability and occurrence, using site occupancy modelling. With the resulting regression equations, we developed distribution maps of both detection probability and required sampling effort throughout the area. Results Of the studied territories, 72.5% were detected as occupied, but after accounting for imperfect detection, the proportion of sites truly occupied was 79%. Detectability decreased in territories with higher topographical irregularity and increased with both the time of day of the survey and the progress of the season. Spatial distribution of detectability showed a mainly north–south gradient following the distribution of slope in the area. The likelihood of occupancy increased with rockier, less forested surface and less topographical irregularity within the territory. A minimum of five surveys, on average, are needed to assess, with 95% probability, the occupancy status of a site, ranging from ≤ 3 to > 24 visits/territory depending on survey‐ and site‐specific features. Main conclusions Accounting for detectability and its sources of variation allows us to elaborate distribution maps of detectability‐based survey effort. These maps are useful tools to reliably assess (e.g. with 95% probability) occupancy status throughout a landscape and provide guidance for species conservation planning.     

Size Bias in Visual Searches and Trapping of Brown Treesnakes on Guam

ABSTRACT The accidental introduction of the brown treesnake (BTS; Boiga irregularis) to the island of Guam after World War II set off a chain of bird, bat, and lizard extirpations. Fortunately, many of the eliminated species have the potential to be restored following population reduction or eradication of the snake. The primary operational tool for population reduction is an effective snake trap, but areas subjected to long-term trapping continue to support BTS, suggesting that some adult snakes are refractory to trapping. We closed a 5-ha area to BTS emigration and immigration and surveyed the population using trapping and visual surveys to determine whether a refractory stratum of adult snakes existed and if trapping was effective for snakes of all sizes. Our surveys included 101 trapping occasions and 109 visual surveys over 309 days, resulting in 2,522 detections of 122 individuals. We detected 44 of 45 supplemented snakes by this intensive sampling effort, which also revealed that trapping was fully effective for snakes >900 mm in snout—vent length (SVL), partially effective for snakes 700–900 mm SVL, and totally ineffective for smaller juveniles (350–700 mm SVL). Visual searching was effective for snakes of all sizes. As BTS mature at approximately 950-1, 050 mm SVL, continuous trapping should suffice to eliminate recruitment in the absence of immigration. Immigration or inadequate effort is most likely responsible for the persistence of BTS in areas subject to long-term trapping. Thus, current efforts to capture trap-refractory adult snakes with alternate control tools are less likely to be successful than immigration barriers alone or in combination with elevated capture effort.     

Determining woodpecker diversity in the sub‐Himalayan forests of northern India using call playbacks

ABSTRACT Tropical forests have exceptional woodpecker diversity, but little is known about the abundance and diversity of woodpeckers in the Indian subcontinent, particularly for the Shorea robusta‐dominated moist deciduous forests of northern India. Our objective was to compare the number of woodpecker species and number of individuals detected using playback surveys and visual/aural transect surveys at five sites. Each site was surveyed 5–6 times along a 2000‐m transect, with woodpeckers detected using two methods: (1) visual and aural cues, and (2) playing back calls of 13 species at 400‐m intervals. Both methods involved similar effort per survey (100–110 min). During surveys, we detected 11 species of woodpeckers. More species and more than twice as many individuals were detected during playback surveys than during visual/aural surveys. In addition, species accumulation curves showed that we detected the species known to be present based on previous work faster with playback surveys than with visual/aural surveys at four of the five sites. During field trials, 97% of targeted individuals (N= 269) of 12 species responded to playback, and 83% of the responses occurred within 1 min of broadcast. The number of species of woodpeckers in our study area (11 species) was typical for a structurally diverse, tropical/subtropical moist broad‐leaved forest. Our results demonstrate that playback surveys are more efficient and accurate than visual/aural surveys, and that playback surveys can be useful for assessing and monitoring woodpecker diversity in tropical forests.     

Searching for weed biocontrol agents—when to move on?

‘Classical’ biological control for an exotic weed requires time‐consuming and expensive surveys for natural enemies in the weed's native range. We advocate the use of rarefaction curves to improve survey efficiency, i.e. to determine the minimum sampling effort for discovering most of the potential control agents actually occurring in the weed's native range. Rarefaction (dilution) curves can be used to estimate the number of herbivore species expected on a given number of plants, at sampling sites or regions, using presence/absence data and species frequencies. An analysis of the shape of the rarefaction curves will therefore indicate (a) which sites possibly contain more undiscovered herbivore species and (b) whether sampling new sites is more likely to reveal further herbivores. This approach is illustrated with two case studies of insect surveys, of root and flower head feeders on Centaurea maculosa (Asteraceae) in Europe and for flower head feeders of various Asteraceae in Brazil. Finally, we consider consequences of combining this approach with focussed searches in the centre of endemism and propose a general survey protocol for natural enemies associated with a host plant in its native range.     

Using species accumulation curves to estimate trapping effort in fauna surveys and species richness

Abstract The shape of species accumulation curves is influenced by the relative abundance and diversity of the fauna being sampled, and the order in which individuals are caught. We use resampling to show the variation in species accumulation curves caused by the order of trapping periods. Averaged species accumulation curves calculated by randomly assigning the order of trapping periods are smooth curves that are a better estimate of species richness and a more useful tool for determining the trapping effort required to adequately survey a site. We extend this concept of randomly resampling the trapping period to show that randomizing the number of individuals caught for each species over the number of collection periods (e.g. days) can provide an accurate estimate of the averaged species accumulation curve. This is particularly useful as it enables an accurate estimation of the proportion of the total number of species caught in an area during a survey from information on the number of individuals caught for each species and the number of trapping periods, and is not dependent on having knowledge of the trapping period in which each individual was caught. This calculation also enables an assessment to be made of the adequacy of fauna surveys to report a species inventory in environmental impact assessments when only a species list and relative abundance data are provided.     

Unveiling the Limitations of Scat Surveys to Monitor Social Species: A Case Study on River Otters

Abstract: We examined the relationship between the production of sites with feces (i.e., latrines) and river otter (Lontra canadensis) abundance to determine whether scat surveys were adequate for monitoring relative population size for species leaving activity signs in a clumped distribution on the landscape. We conducted winter riparian transects to simultaneously monitor otter abundance via snow tracks and latrine sites along the rivers of Kouchibouguac National Park and surrounding area in New Brunswick, Canada. Our data showed that latrine abundance poorly reflected otter abundance for given stretches of rivers because the relationship was nonlinear and reached a plateau. The number of latrine sites was not related to the time period since last snowfall, which indicated that otters repetitively defecated at the same sites. Individual otters and groups did not produce activity signs over larger distances as a function of time, which indicated that they tend to stay in their home ranges in winter. We discuss why scat survey protocols based on determining presence—absence of a species at predetermined search sites may poorly reflect population size, as well as population fluctuations in time. Caution is advised when interpreting data from such surveys for species for which feces or other activity signs surveyed play a role in intraspecific communication and tend to be in a clumped distribution on the landscape.