Sampling communities of ground-foraging ants: Pitfall catches compared with quadrat counts in an Australian tropical savanna

The relative abundances of ant species captured in pitfall traps was compared with those obtained by direct counts in quadrats at a savanna site in Kakadu National Park, Northern Territory. Two measures of abundance in traps were used, one based on total numbers of ants, the other on species frequency of occurrence. All species commonly recorded in quadrats were collected in traps, and their relative abundances were highly correlated on all occasions. Of the 20 most common species in quadrats, five occurred with a significantly different (in all cases lower) frequency in pitfall traps, but these species represented only 1.8–3.1% of total quadrat counts. Results from quadrats and pitfall traps were particularly similar (r > 0.8) when species-were classified into functional groups. Frequency data from traps may sometimes overestimate the abundance of widespread, solitary foraging species (e.g. ‘Chelaner’ and Tetramorium spp.) and underestimate species with large colony sizes (e.g. Iridomyrmex spp.). Data based on total numbers of ants in traps may be more prone to distortion arising from species differences in locomotor behaviour. Species counts in traps could be scaled to reduce these distortions. The finding that pitfall traps gave results comparable with those from quadrat counts provides support for the use of pitfall traps in studies of Australian ant communities in open habitats.     

Methods of estimating ungulate populations in tropical forests

Pellet group counts, drive counts and track counts were used to estimate population abundances of one small and four large species of duiker (Cephalophus sp.) in a moist evergreen forest in northeastern Zaire. Procedures to develop estimates based on line transect counts of pellet groups are described. The Fourier Series estimator proved to be useful for estimating densities of pellet groups. Comparisons were made between population abundance in heavily and lightly hunted areas, and between small and large species. The three census methods were consistent in showing no significant difference between animal abundance in the hunted populations or between abundances of the smaller species relative to the larger species. All methods showed potential as population indices for assessing trends of rare and elusive species in forest environments. Drive counts and pellet group counts may also be useful for estimating densities.     

Is pitfall trapping a valuable sampling method for grassland Orthoptera?

Common methods to assess diversity and abundance of Orthoptera are sweep netting, transect counts and box-quadrat sampling. Pitfall trapping, by contrast, is rarely used, and the value of this method is still being questioned. In 2008, we studied Orthoptera species richness and abundance in five vegetation types along a gradient of dune succession on the Baltic Sea island of Hiddensee (NE Germany) by comparing transect-count and pitfall-trapping data. Using transect counts, 12 species were detected in the study area. With pitfall traps, three chorto- and thamnobiont Ensifera species (C. dorsalis, M. roeselii and T. viridissima) were not caught at all, and it was only in low-growing and sparsely-vegetated grey dunes that all present species were detected. With pitfall traps, the proportion of present species recorded strongly declined with increasing height and density of the vegetation type. Assuming that transect counts are a good proxy for relative Orthoptera densities, densities ascertained by pitfall traps are strongly biased by vegetation structure and locomotive behaviour of the species. More than 80% of all individuals were caught in sparsely-vegetated grey dunes. Frequency patterns of the species also differed. Using pitfall traps, especially chortobiont species were significantly underrepresented. Qualitative and quantitative sampling of Orthoptera using pitfall traps seems only reasonable in habitats with low and sparse vegetation and a high proportion of geobiont species.     

Land hermit crab (Coenobita clypeatus) densities and patterns of gastropod shell use on small Bahamian islands

Aim To examine patterns of abundance, density, size and shell use in land hermit crabs, Coenobita clypeatus (Herbst), occurring on three groups of small islands, and to determine how these variables change among islands. Location Small islands in the Central Exuma Cays and near Great Exuma, Bahamas. Methods Land hermit crabs were captured in baited pitfall traps and were separately attracted to baits. A mark–recapture technique was used in conjunction with some pitfall traps monitored for three consecutive days. The size of each crab and the type of adopted gastropod shell were recorded, along with physical island variables such as total island area, vegetated area, island perimeter, elevation and distance to the nearest mainland island. Results Relative abundances, densities and sizes of crabs differed significantly among the three island groups. Densities of land hermit crabs were as high as 46 m⁻² of vegetated island area. In simple and multiple linear regressions, the only variable that was a significant predictor of the abundance of hermit crabs was the perimeter to area ratio of the island. Patterns of gastropod shell use varied significantly among the island groups, and the vast majority of adopted shells originated from gastropod species that inhabit the high intertidal and supratidal shorelines of the islands. Main conclusions Although densities of land hermit crabs varied, they were relatively high on many islands, and land hermit crabs may play an important role in these insular food webs. Patterns of shell use may be strongly restricted by island geomorphology: irregular shorelines provide relatively more habitat for the gastropod species that account for the majority of adopted shells and the steep sides of the islands prevent the accumulation of marine gastropod shells. The size of adult hermit crabs appears to be limited by the relatively small gastropod shells available, while the abundance of hermit crabs may be limited by the number of shells available.     

The energetic equivalence rule rejected because of a potentially common sampling error: evidence from carabid beetles

Abundance data from pitfall traps are widely used to estimate the relationship between beetle body size and abundance. Such data probably overestimate densities of large bodied species and may overestimate slopes of size‐abundance relationships. Here, we test this idea by comparing size‐abundance patterns found using data from pitfall trapping with those found with data from a quantitative method of estimating abundance, quadrat sampling. We use data from a total of 47 communities. As expected, slopes of size‐abundance relationships are significantly more positive when estimated using data from pitfall traps compared to when using quadrat sampling data. This was seen when looking across different communities, within communities sampled by both methods and when focusing on the set of species found by both methods within a community. These results were also generally found regardless of method of analysis, which were done using regression with species values as independent data points and using the independent contrast method, and with slopes estimated using ordinary least square regression or the structural relation. Most important, slopes of size‐abundance relationships based on data from pitfall traps were on average significantly more positive than ?0.75 on log–log scales, and thus inconsistent with the energetic equivalence rule. Slopes based on quadrat sampling, on the other hand, were on average not significantly different from ?0.75. The rejection of the energetic equivalence rule based on data from pitfall traps here is therefore a sampling artefact. Similar problems may apply to abundance data from virtually all insect trapping methods, and should make us consider re‐examining many of the size‐abundance patterns documented so far. As a large proportion of all animal species are insects, and traps are widely used to estimate abundance, this is a potentially important problem for our general understanding of the relationship between species body size and abundance.     

A comparison of pitfall traps with bait traps for studying leaf litter ant communities.

A comparison of pitfall traps with bait traps for sampling leaf litter ants was studied in oak-dominated mixed forests during 1995-1997. A total of 31,732 ants were collected from pitfall traps and 54,694 ants were collected from bait traps. They belonged to four subfamilies, 17 genera, and 32 species. Bait traps caught 29 species, whereas pitfall traps caught 31 species. Bait traps attracted one species not found in pitfall traps, but missed three of the species collected with pitfall traps. Collections from the two sampling methods showed differences in species richness, relative abundance, diversity, and species accumulation curves. Pitfall traps caught significantly more ant species per plot than did bait traps. The ant species diversity obtained from pitfall traps was higher than that from bait traps. Bait traps took a much longer time to complete an estimate of species richness than did pitfall traps. Little information was added to pitfall trapping results by the bait trapping method. The results suggested that the pitfall trapping method is superior to the bait trapping method for leaf litter ant studies. Species accumulation curves showed that sampling of 2,192+/-532 ants from six plots by pitfall traps provided a good estimation of ant species richness under the conditions of this study.     

Assessment of population biology,size-weight relationship,condition factor,and spatial distribution of the mangrove crab Ucides cordatus (Crustacea: Ocypodidae) in southern Brazil

Brachyuran crabs are considered one of the most representative groups in mangroves, being recognised as mangrove engineers. However, species that present commercial interest may have their population structure and spatial distribution affected by human activities, such as crab capture. Therefore, monitoring populations over time is essential. We investigated the population biology, size-weight relationship, condition factor and spatial distribution of Ucides cordatus in a mangrove ecosystem from southern Brazil, providing information for population status assessment. Males and females differed in abundance and frequency, body size, size-weight relationship and condition factor. Nonetheless, they presented the same spatial distribution pattern. Abundance, sex ratio and body size also revealed a possible influence of anthropised areas in the configuration and distribution of the species. Our results indicate a possible increase in the exploitation of the species, mainly due to the decrease of the largest male size classes’ frequency. Interspecific competition seems to be a possible biotic factor influencing its condition factor. The spatial species distribution highlighted the importance of sites with less anthropogenic influence for the maintenance of the species that can be considered as key areas for the conservation of the U. cordatus in Babitonga Bay.     

Arthropod diversity and allochthonous-based food webs on tiny oceanic islands

Very small islands, on the order of a few hundred square metres in area, have rarely been the focus of ecological investigations. I sampled nine such islands in the central Exumas, Bahamas for arthropod species abundance and diversity using a combination of pitfall traps, pan traps and sticky traps. Three islands had no terrestrial vegetation, three islands contained only Sesuvium portulacastrum L., a salt‐tolerant perennial that had been experimentally introduced 10 years ago, and three islands supported one or two naturally occurring plant species. A relatively diverse arthropod assemblage was discovered, including representatives of 10 different orders of Crustacea and Insecta. Land hermit crabs were the most abundant crustaceans, and dipterans were the most abundant and speciose insects. Two of the most common insects were previously undescribed species. Measures of arthropod species abundance and diversity were not significantly different for vegetated vs. non‐vegetated islands. All 10 orders were present on bare islands, and nine of them were present on vegetated islands. Measures of arthropod species abundance and diversity were positively associated with island area, and negatively associated with distance from the nearest large island. Hypothesized food webs consist of several trophic levels and have strong allochthonous inputs. Tiny islands such as these hold insights into early successional processes and the base of insular food webs.     

Optimising sampling methods for small mammal communities in Neotropical rainforests

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Developing methods for quantifying the apparent abundance of fiddler crabs (Ocypodidae: Uca) in mangrove habitats

Counting the number of individuals emerging from burrows is the most practical method for estimating the apparent abundance of Australian Uca species living in mangrove habitats. Experiments were conducted to investigate the effect on counts of quadrat design, distance of observer, quadrat size, recovery time and observational technique. Significant differences in the apparent abundance of one species were found when the subjects were within 2 m of the observer, and when a conspicuous quadrat was used. The largest quadrat tested provided the least variability in counts but an intermediate size (0.56 m²) was more practical. Most Uca active within a 30-min period emerged during the first 10 min regardless of site, species, sex or season. There was a linear correlation between scanning and continuous observation indicating that the former method could be useful when sampling time was limited. Temporal changes in the apparent abundance of Uca suggest that long-term sampling and more detailed studies will be worthwhile.     

Hermit crabs, humans and Mozambique mangroves

There is a complex interrelationship between upper shore hermit crabs (such as Coenobita sp. and Clibanarius sp.), coastal human populations and mangrove forests in Mozambique. The abundance, activity, shell selection and behaviour of three species of hermit crab are related to the level of mangrove cover. With increased density of mangrove trees, the study species of hermit crab changed in abundance, tended to become diurnal, spent more time feeding and were clustered in larger groups when doing so, and selected longer spired shells. All five of the same variables are also linked to the proximity and activity of humans through both direct and indirect actions. Direct effects included a tendency to nocturnal activity with proximity to human activity; indirect effects included increased and more clumped food supplies, and shell middens from intertidal harvesting and deforestation. Mangroves are important to local human populations as well as to hermit crabs, for a wide variety of (similar) reasons. Mangroves provide storm shelter, fisheries and fishery nursery grounds for adjacent human settlements, but they also harbour mosquito populations and their removal provides valuable building materials and fuel. Hermit crabs may be useful (indirectly) to coastal human populations by being a source of food to certain commercial species, and by quickly consuming rotting/discarded food and faeces (thereby reducing disease and pests). They can also cause minor problems to coastal human populations because they use shells of (fisheries) target mollusc species and can be more abundant than the living molluscs, thereby slowing down effective hand collection through confusion over identification. The mixture of positive and negative attributes that the three groups impart to each other in the Quirimba Archipelago, northern Mozambique, is discussed.     

Restoration promotes ecological functioning through greater complementarity

Restoration projects are increasingly widespread and many promote habitat succession and the diversity and abundance of faunal communities. These positive effects on biodiversity and abundance may extend to enhancing the ecological functioning and resilience of previously degraded ecosystems, but this is rarely quantified. This study surveyed a 200-ha restoring coastal wetland and three control wetlands in the Maroochy River, eastern Australia to compare the effects of wetland restoration on the consumption of carrion and the biodiversity, abundance, and functional diversity of functionally important fish and crustaceans. Carrion consumption by fish and crustaceans was measured every 6 months from spring 2017 until spring 2021 for nine events using a combination of baited cameras and scavenging assays. We found restoration improved rates of carrion consumption and the biodiversity, functional diversity, and abundance of scavenger species. Despite positive effects on the diversity of scavengers and carrion consumption, the abundance of two species, longfin eels (Anguilla reinhardtii) and mud crabs (Scylla serrata), was the most important predictors of carrion consumption rates. The spatial distribution of carrion consumption was concentrated in areas with high saltmarsh extent, moderate to high mangrove extent, and high salinity, which also resembled the distribution of both longfin eels and mud crabs. We show that restoration can promote the rates of key ecological functions but that increases to functions are likely to be characterized by low functional redundancy and greater complementarity. Therefore, maintaining or increasing the abundance of functionally important species should become a key objective in future restoration projects.     

Can Malaise traps be used to sample spiders for biodiversity assessment?

Malaise traps are typically used to sample a range of flying insect groups; however non-target taxa such as spiders may also be collected in large numbers. In this study, spiders were sampled in peatlands and wet grasslands and catches in Malaise and pitfall traps were compared in order to determine the adequacy of Malaise traps for use in spider biodiversity assessment. Overall, the number of species and individuals caught in Malaise and pitfall traps were comparable, although more species were sampled in Malaise traps in locations with a greater structural diversity of the vegetation. The spider fauna sampled by the Malaise traps differed from that of the pitfall traps, but both methods consistently separated the species assemblages by biotope. These results demonstrate that Malaise traps are effective at sampling spiders and indicate that they can be used in biodiversity assessment. In addition the complementary species sampled by each method mean that employing both techniques will be useful where a full inventory of the species is required. The authors do not suggest that Malaise traps should be used solely to sample spiders; however, if traps are set to collect insects, identification of the spiders sampled may reduce the need to employ additional sampling techniques.     

Preliminary investigations into a potential ant invader in Kruger National Park,South Africa

The super‐abundance of Lepisiota incisa (Forel) in settlement areas of Kruger National Park, South Africa has raised concerns that it might be exotic and could negatively impact on natural ecosystems. We documented the current distribution of this ant species around the main settlement in Kruger, assessed how ant diversity varies across habitats, and investigated potential mechanisms facilitating dominance by L. incisa. Around the main camp of Skukuza, pitfall traps were set in five habitats differing in anthropogenic influence. Baiting trails were conducted to determine whether L. incisa and native ants differed in numerical and behavioural dominance. Aggression assays were performed on L. incisa to provide information on colony structure. Although L. incisa was found in all habitats, it had a significantly higher abundance in gardens and appears confined to human‐disturbed areas. It was numerically dominant recruiting more workers to food baits than all other ant species combined. Aggression levels were low between most nests of L. incisa indicating a potential supercolony structure. More information is urgently needed on the genetics, physiology and origins of L. incisa, and monitoring of its current distribution is recommended. This species warrants attention because there may be significant potential for overseas invasion.     

笼捕法和陷阱法对森林小型兽类多样性监测效率比较

<正>小型兽类包括食虫目(Insectivora)、啮齿目(Rodentia)、翼手目(Chiroptera)、兔形目(Lagomorpha)等,物种数量多,分布广,适应能力强,对环境变化敏感,因此其群落组成和种群数量变化可较好地反映生境变化的质量和人类活动的干扰程度(肖治术等,2002;李俊生等,2003;仝磊和路纪琪,2010)。小型兽类多样性一直是生物多样性和生态环境监测与评价的重要指示类群之一(周立志和马勇,2002)。统计动物毛发、粪便、巢穴、叫声、足迹等动物痕迹以及直接观察等方法已被广泛用于兽类物种监测和种群密度估计(Eberhardt and Van Etten,1956;Bider,1968;Gannon     

Tropical ant communities are in long-term equilibrium

Communities change with time. Studying long-term change in community structure permits deeper understanding of community dynamics, and allows us to forecast community responses to perturbations at local (e.g. fire, secondary succession) and global (e.g. desertification, global warming) spatial scales. Monitoring efforts exploring the temporal dynamics of indicator taxa are therefore a critical part of conservation agendas. Here, the temporal dynamics of the Otongachi leaf litter ant community, occurring in a cloud forest in coastal Ecuador, were explored. By sampling this community six times over eleven years, I assessed how the ant fauna caught by Winkler traps (more diverse and cryptic fauna) and caught by pitfall traps (larger, more mobile fauna) changed over time. The Otongachi leaf litter ant community was dynamic. Although species richness in the community remained constant, temporal turnover of species was high: on average, 51% of the ant species in Winkler traps, and 56% of those in pitfall traps, were replaced with other ant species from one year to the other. Shifts in the rank abundance of species in the community were also large across the eleven years and, on average, shifts in the rank abundance of species collected by Winkler traps doubled those occurring in pitfall traps from one census to the other. In spite of these trends, the Otongachi ant fauna showed no (Winkler) or weak (pitfall) evidence of directional change (towards a new community). Thus, this tropical ant community can be divided in two community compartments. The Winkler compartment composed by a more diverse and cryptic ant fauna appears to be resilient and stable in time. The pitfall compartment composed by larger and more mobile ants may be prone to respond to disturbance. This study suggests that 1) species appearing/disappearing from a site may be rather the rule, difficult to separate from responses to ecological stress. 2) Conclusions made in short-term studies, or studies comparing two (e.g. before and after) snapshots of a community, should thus be revisited. Finally, 3) the ant fauna caught by pitfall traps (a rather simple and cheap survey method) is the most likely community compartment to indicate ecological perturbation. This study adds to the growing evidence that using ants as ecological indicators should incorporate long-term temporal dynamics.     

Effectiveness and utility of acoustic recordings for surveying tropical birds

ABSTRACT Although acoustic recordings have recently gained popularity as an alternative to point counts for surveying birds, little is known about the relative performance of the two methods for detecting tropical bird species across multiple vegetation types. During June and July 2008, we collected species detection/nondetection data to compare the performance of a quadraphonic acoustic recording system and point counts for estimating species richness and composition and detection probabilities of 15 rare, moderately common, and common tropical bird species across six structurally distinct vegetation types (coastal dune scrub, mangrove, low‐stature deciduous thorn forest, early and late successional medium‐stature semievergreen forest, and grazed pastures) in the northern Yucatan Peninsula. We selected five rare species endemic to the Yucatan Peninsula and 10 moderately common and common species that also occur in other tropical regions. Species richness and composition did not differ between survey methods in any of the vegetation types. At the population level, however, we found support for an effect of method on detection probability for most species. For 13 species, regardless of their abundance, acoustic recordings yielded detection probabilities as high as or higher than those for point counts across all vegetation types. The remaining two species were better detected by point counts in pastures and coastal scrub, where greater visibility likely improved sightings of these species. However, these species were detected as well as or better by acoustic recordings in forests and mangroves where detections were primarily auditory. In tropical regions where experienced field observers may not be available and funding for field surveys may be limited, acoustic recordings offer a practical solution for determining species richness and composition and the occupancy patterns of most species. However, for some species, a combination of methods will provide the most reliable data. Regardless of the method selected, analyses that account for variation in detection probability among vegetation types will be necessary because most species in our study demonstrated vegetation‐dependent detection probabilities.     

红树林湿地相手蟹科动物摄食生态研究进展

相手蟹科物种是红树林湿地的主要底栖动物类群,在生态系统中起着重要的作用。我国大陆地区目前已记录的相手蟹科物种数量为12种,低于其它红树林地区(国内常用的采样方法会造成螃蟹物种数量和密度的低估),其中褶痕相手蟹(Sesarma plicata)、无齿相手蟹(S.deaani)和双齿相手蟹(S.bidens)等是常见种。红树植物叶片是相手蟹科动物的主要食物来源,相手蟹科动物通过地表摄食和洞穴贮存的形为消耗了大量的红树植物凋落叶,使这些凋落叶的有机质和营养元素得以保留在生态系统内,在凋落叶的周转和物质归还方面起到重要的作用。它们同时也摄食红树植物的繁殖体并且对不同物种的繁殖体具有摄食偏好,这可能对一些红树物种的植被更新能力和红树植被群落结构产生影响。相手蟹科动物对不同物种和不同状态的红树叶片也存在摄食偏好,通常对腐烂的叶片摄食偏好较强;螃蟹的摄食偏好与叶片的营养成份、粗纤维和单宁含量以及C/N比等性质有关;但在恶劣的野外环境下,螃蟹则会表现出随机性摄食。目前关于相手蟹科动物生态学作用的认识仍不充分,例如它们的种群大小和对凋落物的转化作用等,有待于进一步研究。     

The effects of rainforest canopy loss on arboreal dung beetles in Borneo: implications for the measurement of biodiversity in derived tropical ecosystems

We examine the effect of selective timber extraction, and corresponding forest canopy loss, on arboreal dung beetles in the tropical rainforests of Sabah, Malaysian Borneo. Changes in vertical distribution of beetles are measured through differences in the abundance of beetles in ground-based pitfall traps in primary, logged and plantation forest. Previous research has demonstrated that arboreal dung beetles are not generally collected in pitfall traps in primary forest, but are present in large numbers above the ground in canopy vegetation: the presence of arboreal beetles in pitfalls in areas of reduced or modified canopy cover may therefore reflect a response to the absence or modification of their usual habitat, and the proliferation of these beetles nearer to the ground. In this paper, statistically significant differences are found in the abundance of beetles in ground pitfall traps from logged forest compared to primary forest. Results show that virtually no arboreal dung beetles are recorded in primary forest traps, with an increased abundance of arboreal dung beetles in traps from logged and plantation forest, with 1.72% of the total number of arboreal beetles recorded from primary forest, 22.32% from logged forest, and 75.96% from plantation forest. The presence of arboreal dung beetles in plantations demonstrates that arboreal dung beetles can survive outside their normal habitat, and we relate these observations to adaptations to upper rainforest canopy conditions, and proliferation of these microclimatic conditions in man-made habitats. Results are also discussed in terms of their relevance to the measurement of species richness and diversity in logged and other derived ecosystems, where mixing of the ground-based and arboreal faunas occurs.     

A comparison of alternative methods for estimating population density of the fiddler crab Uca annulipes at Saco Mangrove, Inhaca Island (Mozambique)

Visual counts of surface-active crabs both by binocular and burrow counting methods have been used in many studies to estimate population density. However, their reliability has not yet been assessed comparatively. Three methods for estimating the abundance of fiddler crabs Uca annulipes in a mangrove forest (Inhaca Island, Mozambique) were compared from three different sub-areas: two sub-areas inundated only during spring tides and one sub-area inundated in both spring and neap tides. Burrow, binocular and direct (excavation) counting methods were performed by plotting ten 0.25 m² quadrats in each sub-area over the four moon phases. Overall densities (per 0.25 m²) differed according to method, sub-area and lunar phase. Burrow count overestimated crab density by up to 20%, while binocular count underestimated density by up to 41%. Correlation coefficient estimated for both counting methods showed that burrow count gives better density estimates than binocular count (0.91 and 0.56, respectively). Sex ratios were also investigated within the three sub-areas and at the moon phases. Males are dominant throughout the studied period except during new moon and first quarter, indicating that when the number of gravid females is low, sex ratio bias for binocular count is minimal.