Hubert Höfer

Structure and function of soil fauna communities in Amazonian anthropogenic and natural ecosystems

The soil biological conditions of two 5-year-old polyculture tree plantations in Amazonia were studied comparatively to a 13-year-old secondary forest and a nearby undisturbed primary forest. The polycultures had been planted to regenerate the soil degraded by land preparation and a former rubber tree monoculture. Abundance and biomass of functional groups of soil meso- and macrofauna were measured at three-months-intervals over 2 years and litterbag experiments with fauna exclusion were carried out. This paper concentrates on the description of the structure of the soil fauna communities, forming the background for an evaluation of the decomposition processes in polyculture plantations. Decomposition rates were strongly determined by the macrofauna particularly in primary forest, where large earthworms, termites and ants dominated the soil fauna. In the plantations, where litter originated predominantly from the non-planted, adventitious vegetation, an abundant decomposer fauna was found, in which however other groups or species dominated. Although decomposition rates in the plantations were about 60 % lower and soil biological variables like organic matter-, nitrogen-content and water holding capacity were slightly lower than in the primary forest, conditions seem favourable for a manipulation of the soil fauna by management of secondary vegetation and litter quantities.

Litter fall, litter stocks and decomposition rates in rainforest and agroforestry sites in central Amazonia

The sustainability of agroforestry systems in Amazonia was assessed from their litter dynamics and decomposition. Litter fall and litter stocks were determined from July 1997 to March 1999 in four sites in central Amazonia: a primary rainforest, a 13-year-old secondary forest, and two sites of a polyculture forestry system which consisted of four planted tree species of commercial use amidst upcoming secondary growth. The average annual litter fall in the undisturbed primary rainforest (FLO) was 8.4 t ha−1 year−1, which is within the range of litter fall in other rainforests in the region. It was similar in one of the two polyculture sites (8.3 t ha−1 year−1), but lower in the secondary forest and in the second polyculture site. In the litter fall in secondary forest and agroforestry sites, the leaf portion was higher (76–82% of total litter fall) than in FLO, due to reduced fine matter and wood fall. Leaf litter fall variability was much lower in the plantation sites than in the forests, which is explained by the much more homogeneous stand structure of the plantations. The quality of the produced litter, measured as C/N ratio, differed significantly between the primary forest site and one polyculture and the secondary forest site. The cumulative input of nitrogen through litter fall was 144 kg ha−1 year−1 in FLO, and 91–112 kg ha−1 year−1 in the polycultures and the secondary forest. Litter fall was not correlated with soil parameters, but had a significant linear regression with canopy closure. For the primary rainforest, litter fall was also (inversely) correlated with monthly rainfall. Litter fall was higher in the first year (1997–1998; an El Niño period) than in 1998–1999. Litter stocks on the forest floor were highest in the secondary forest (24.7 t ha−1), and much lower in the polyculture sites (15.1–16.2 t ha−1) and the primary forest (12.0 t ha−1). There were no differences in the relative N content (C/N ratio) of the litter stocks between the sites, but the larger stocks led to higher absolute N contents in the litter layer in the secondary forest. From the monthly values of litter stocks (S) and litter fall (P), the decomposition coefficient ke=P/S was calculated, which was, on average, highest for the primary forest (0.059), followed by the polyculture systems (0.040–0.042), and by the secondary forest (0.024). Thus, due to low decomposition rates, the secondary forest site showed large litter accumulations in spite of a relatively low litter fall. In contrast, the primary forest showed high litter fall but low stocks, due to high decomposition rates. The decomposition coefficients of the polyculture systems ranged between the primary and the secondary forest. The reduced decomposition rates in the man-managed agroecosystems indicate quantitative and/or qualitative changes in the decomposer communities of these systems that lead to a higher build-up of litter stocks on the forest floor. However, the decomposer systems in the polyculture sites still were more functional than in the site of non-managed secondary growth. Thus, from a soil biological viewpoint, ecologically sustainable low-input agroforestry in Amazonia will benefit from the application of these polyculture systems.

Microclimate in agroforestry systems in central Amazonia: does canopy closure matter to soil organisms?

Microclimate was recorded and soil organisms were collected 1997-1999 in ecosystem stands of contrasting structure in central Amazonia (a primary forest, a 12-year secondary forest, two different agroforestry systems, a rubber tree (Hevea brasiliensis) plantation, and a peach palm (Bactris gasipaes) monoculture with a densely closed canopy). The aim was to look at the effects of canopy closure on microclimate and soil organisms. Monthly maxima temperature, average air and soil temperatures, and saturation deficit were highest in September 1997, and total annual rainfall in 1997 was 12-28% lower than in the other study years. The monthly average litter temperatures were consistently 2-4 °C higher in the plantation sites than in the rainforest and the secondary forest, and temperatures on single days (not the monthly averages) in the plantations were up to 10 °C higher than in the primary forest. The highest average litter and soil temperatures and the highest temperature maxima were recorded in the agroforestry plantations. Canopy closure strongly determined the litter temperatures in the sites. Soil macrofauna biomass was also strongly correlated to canopy closure (linear regression, P = 0.05). We conclude that a well developed canopy effectively protects the soil macrofauna from high temperature variation and drought stress. Therefore, optimizing these agroforestry systems for canopy closure may contribute to a better management of the beneficial soil decomposer community.

Litter decomposition, microbial biomass and activity of soil organisms in three agroforestry sites in central Amazonia

Soil organisms play a central role in the decomposition of organic matter. The activity of soil organisms was comparatively examined in three experimental sites in central Amazonia (Brazil): a peach palm monoculture (Bactris gasipaes) a, rubber tree plantation (Hevea sp.), and an agroforestry system (four tree species planted in rows, the space between covered by upcoming secondary vegetation). The overall decomposition rates in the systems and the role of different groups of soil organisms (macrofauna, mesofauna, microflora) were studied with leaf litter (Vismia guianensis) enclosed in litter bags. Microbial respiration and biomass (SIR method) in litter and soil were measured (IRGA). Microbial respiration in all sites decreased in the gradient litter > topsoil (0–5 cm) > soil at 5–15 cm. The highest decomposition rate was always observed in the litter bags of coarse mesh size, pointing to the crucial role of the macrofauna in maintaining a high decomposition rate of the organic material in all systems. The Hevea (k = 3.4) and the Bactris plantation (k=3.1) both showed the highest decomposition rates, followed by the polyculture system (k=1.9). The Bactris plantation also had the highest level of microbial respiration and biomass in litter and soil. We discuss these findings in the light of data on rainfall, pH and canopy closure. They suggest that microclimate is a more important factor than biomass in determining litter decomposition rates and activity of soil organisms at these sites.

Feeding activities of soil organisms at four different forest sites in Central Amazonia using the bait lamina method

A recently developed technique in soil ecology is the use of the bait lamina method, for assessing the feeding activity of soil animals in situ. Here the bait lamina method (slightly adapted to tropical conditions) was used for the comparison of four closely situated sites (a primary rain forest, a secondary rain forest and two mixed- species tree plantations) in the Brazilian Amazon (project SHIFT ENV-52). The total feeding activity (portion of empty apertures in a set of laminae) and the vertical distribution of the feeding activity were evaluated for differences between the sites. The feeding activities in the primary and secondary forest were at the same level and significantly lower than in the two plantations. Feeding activity in subplots where surface litter has been experimentally removed was significantly lower than in the controls with the litter layer intact, at all four sites. The abundance of soil macrofauna or Enchytraeidae was not correlated with the results of the bait lamina tests, while the abundance of mesofauna (probably mainly Oribatida) was consistent with the pattern of feeding activity. The feeding activities as determined with bait laminae did not correlate with the decomposition activities determined with litterbags. Due to the easy applicability in combination with its feasibility for statistical evaluation and its consistent responses to site differences in experimental treatments we consider the bait lamina method to be a promising approach for the biological assessment of tropical soils.

ADULT SIZE OF EIGHT HUNTING SPIDER SPECIES IN CENTRAL AMAZONIA: TEMPORAL VARIATIONS AND SEXUAL DIMORPHISMS

Abstract We studied temporal variation in adult size and sexual size dimorphism (SSD) of seven hunting spider species, Ctenus amphora, C. crulsi, C. manauara, C. villasboasi (Ctenidae), Phoneutria fera, P. reidyi (Ctenidae), and Ancylometes rufus (Pisauridae) in a tropical rainforest, and one species from a relatively open vegetation habitat, C. minor, in central Amazonia. Size variation was great within and among field trips. Spiders were generally smaller in October (end of dry season) when compared with other months: adults of C. amphora, C. crulsi and C. manauara were significantly smaller in October 1995 when compared to February 1996; P. fera were smaller in October 1998 than in June 1998; and A. rufus were smaller in October 1998 than in August 1998. The temporal variation in size is possibly a result of low prey availability during the dry season. Six species had significant differences in prosoma length between males and females: C. amphora, C. crulsi, C. manauara and C. minor had larger males (which is considered rare in spiders), and P. reidyi and P. fera had larger females. However, considering an alternative index of size, the “rough area” (an approximate measure of the area of the spider as seen from above), the males were significantly larger for all species (up to 2.8 times in C. minor), because they have longer legs relative to their prosoma length. We suggest that selection for high mobility may be the reason for adult males with longer legs, and that the smaller species had higher degrees of sexual dimorphism in leg length because of the relative size of obstacles in the leaf litter. RESUMO. Estudamos a variação temporal de tamanho de adultos e o dimorfismo sexual de tamanho de sete espécies simpátricas de aranhas errantes, Ctenus amphora, C. crulsi, C. manauara, C. villasboasi (Ctenidae), Phoneutria fera, P. reidyi (Ctenidae), e Ancylometes rufus (Pisauridae) em uma floresta tropical úmida, e uma espécie em um habitat de vegetação relativamente aberta, C. minor, na Amazônia Central. A variação de tamanho foi grande dentro e entre excursões de coleta. As aranhas foram geralmente menores em outubro (final da estação seca) comparado com outros meses: adultos de C. amphora, C. crulsi, C. manauara e C. minor foram significativamente menores em outubro de 1995 comparado a fevereiro de 1996: P. fera foram menores em outubro de 1998 do que em junho de 1998 e A. rufus foram menores em outubro de 1998 do que em agosto de 1998. A variação temporal em tamanhos observada é possivelmente um resultado de baixa disponibilidade de presas durante a estação seca. Seis espécies tiveram diferenças significativas em comprimento do cefalotórax entre machos e fêmeas, C. amphora, C. crulsi, C. manauarae C. minor tiveram machos maiores (o que é considerado raro em aranhas), P. reidyi e P. fera tiveram fêmeas maiores. Entretanto, considerando um índice alternativo de tamanho, a “área aproximada” (uma medida da área da aranha em vista superior), os machos foram significativamente maiores em todas as espécies (até 2,8 vezes em C. minor), porque eles têm pernas mais longas em relação ao tamanho do cefalotórax. Nós sugerimos que uma seleção para alta mobilidade pode ser a razão para machos com pernas maiores, e que as menores espécies tem maior dimorfismo sexual no comprimento das pernas devido ao tamanho relativo dos obstáculos na serapilheira.

PATTERNS OF ABUNDANCE OF FOUR SPECIES OF WANDERING SPIDERS (CTENIDAE, CTENUS) IN A FOREST IN CENTRAL AMAZONIA

Abstract We studied spatial and temporal patterns of abundance of Ctenus amphora, C. crulsi, C. manauara and C. villasboasi, four syntopic species of medium-to-large sized wandering spiders that forage on the ground in a neotropical rainforest. We found temporal variation, apparently seasonal, in abundance for two of the four species. The four species are sympatric in the study area, but with very distinct spatial patterns of abundance. Ctenus amphora was more abundant in areas with sandy soil but are also common on clay soils, C. manauara and C. crulsi are the dominant species in areas with clay soil and are infrequent in sandy soils, and C. villasboasi had a more homogenous abundance in the study area. Previous studies suggested that a predator, army ants, could have an important impact on the abundance of these spiders. We estimated the frequency of attacks by army ants using pitfall traps in sandy and clay soil areas. The estimated probability of attack by army ants was higher in areas with clay soil (92% per 3 months), where all species are frequently found, than in sandy soil areas (21%), where C. crulsi and C. manauara were almost absent. However, it is still not clear if predation by army ants is a key factor that facilitates coexistence in clay soils, and this factor can not explain the difference on the dominant species between areas with different soil types. We also discuss the description of spatial patterns of abundance as a simple, but powerful, tool seldom used for preliminary studies on the coexistence of spiders.

A revision of the Neotropical spider genus Ancylometes Bertkau (Araneae: Pisauridae).

The spider genus Ancylometes Bertkau, 1880 is revised. A. vulpes Bertkau, 1880, type species of the genus, is considered a junior subjective synonym of Dolomedes concolor Perty, 1833. Both types are lost and we redescribe the species based on specimens similar to those found at the type locality of A. vulpes. Spiders of the genus are large nocturnal ground-living hunting spiders with a strong affinity in most species, to water bodies within their tropical environment. Those species hunt also on small vertebrates like frogs, tadpoles and fishes. All species show slight sexual dimorphism in colour and body-to-leg-size relations. Females carry brown egg-sacs in chelicerae and build a nursery web. The genus is morphologically diagnosed by the presence of ventral spines on tarsi III and IV in both sexes and by their genital characters: filiform embolus with a basal membranous lobe, wing-like conductor and hammer-like median apophysis in males; female epigyne consisting of two broad lateral plates and a central plate in form of a bike saddle with its nose pointing posteriorly. Ten valid species are recognized and described, five of them are new: Ancylometes japura, A. jau, A. riparius from Amazonas, A. terrenus from Acre, Amazonas and Mato Grosso and A. pantanal from Matto Grosso do Sul, all from Brazil. The female of A. amazonicus is described for the first time and the female of A. hewitsoni for the first time based on an adult specimen. Ancylometes vulpes Bertkau, Ctenus argentinus Holmberg, Ancylometes bolivianus Tullgren, Lycoctenus bahiensis Strand, Lycoctenus selenkae Strand, Lycoctenus paraguayensis Strand, Cupiennius argentinus Petrunkevitch, Ctenus paulensis Mello-Leitao, Cupiennius diplocellatus Mello-Leitao, Ctenus originalis Mello-Leitao, Ctenus iophorus Mello-Leitao, Corinoctenus anomalostomus Mello-Leitao, Ctenus infelix (Mello-Leitao, Ctenus metatarsalis Mello-Leitao, Phoneutria niveobarbata Mello-Leitao and Corinoctenus greenwayi Carcavallo & Martinez are newly synonymized with A. concolor (Perty). Ctenus fuscus Walckenaer, Ctenus giganteus Taczanowski, Ctenus bimaculatus Taczanowski, Leptoctenus tenkatei Hasselt, Lycoctenus brunneus Pickard-Cambridge, Lycoctenus gigas Pickard-Cambridge, Lycoctenus demerarensis Pickard-Cambridge, Lycoctenus saraensis Strand, Lycoctenus paraensis Strand, Ancylometes pindareensis Mello-Leitao, Ancylometes pindareannus Mello-Leitao, Ctenus juruensis Mello-Leitao, Ctenus striolatus Mello-Leitao, Ctenus xerophilus Mello-Leitao and Lycoctenus titanus Caporiacco are newly synonymized with A. rufus (Walckenaer). Lycoctenus palustris Pickard-Cambridge, Ancylometes orinocensis Simon, Lycoctenus venezuelensis Strand, Lycoctenus caracasensis Strand and Ctenus nasutus Kraus are newly synonymized with A. bogotensis (Keyserling). A. valentinei Petrunkevitch, 1925 from Panama is a Cupiennius (new combination) and considered a senior synonym of C. panamensis Lachmuth et al., 1985. The geographical distribution is Neotropical, with one northern widespread species (A. bogotensis) reaching Central America, one widespread species of the Amazon reaching the Sao Paulo coastal area and one widespread species of central Brazil reaching Argentina. From the Amazon region six rarely collected species are described and one species was recently collected in the Pantanal of Brazil.

The earthworm fauna of regenerating forests and anthropogenic habitats in the coastal region of Paraná.

The aim of this study was to evaluate abundance, biomass and diversity of earthworms in the southern coast region of the Mata Atlântica biodiversity hotspot. A total of 51 study sites in pastures, banana monocultures, mixed agroforestry systems, secondary forests in succession and old-growth forests near the coast of Parana, Brazil, were evaluated. Each site was sampled once. Species richness of the earthworms was generally low and varied little between sites. At all sites except for one, the peregrine species Pontoscolex corethrurus (Glossoscolecidae) strongly dominated. Three other peregrine species, Amynthas corticis , Amynthas gracilis (Megascolecidae) and Ocnerodrilus occidentalis (Ocnerodrilidae), were frequent in moist sites. No autochthonous species were found. Abundance and biomass of earthworms varied strongly within and between sites (0-338 individuals m -2 , 0-96 g m - ² fresh weight). Pastures had signifi cantly lower abundance than all other sites. The forest sites had similar earthworm abundance and biomass, with a tendency to be higher in younger succession stages. The coastal plain region has been strongly altered by human activities. Reasons for the lack of any autochthonous species and the dominance of one peregrine species require further investigation.

The spider fauna of neotropical tree canopies in Central Amazonia: First results

The fogging technique was used to collect spiders from tree canopies in the Central Amazon. Spiders were sampled from two canopies of a frequent terra firme rainforest tree species (Goupia glabra Aubl., Celastraceae) during the dry season (August 1991) and the rainy season (February 1992). We present species lists and discuss species inventory, species number, relative abundance and diversity comparing the different samples.