Animal-habitat relationships in the Knysna Forest, South Africa: discrimination between forest types by birds and invertebrates

Abstract

Effects of forest plant species composition and physiognomy on bird and invertebrate communities were investigated in three discrete, relatively undisturbed forest types along a dry-wet soil moisture gradient. Using discriminant function analysis, a 100% floristic and a 78% vegetation structural discrimination were obtained between the three forest types. However, the bird communities of these different forest types were very similar in species composition, and had much lower densities than those normally encountered in other, superficially similar forests. Although an 81% discrimination between forest types was attained through analysis of ground surface invertebrates, measures of litter and aerial invertebrate abundance were also of limited use as discriminators. Historical and biogeographic factors, as well as the low nutritional levels in the soil and vegetation may be the causes of low bird and invertebrate density and diversity. It is concluded that floristics and vegetation structure have, at best, a minor influence on bird community structure, and possibly also on invertebrate community structure in the Knysna Forest.

The relative influence of competition and prey defences on the trophic structure of animalivorous bat ensembles

“…Moths were the most abundant medium-and large-sized insect prey found in the light traps. Insect abundance declined to low levels during the winter months at all ensembles, consistent with evidence from other studies that sampled insect abundance in the fynbos (McDonald et al 1990;Schoeman and Jacobs 2003), forest (Koen and Crowe 1987) and savanna (Rautenbach et al 1988) biomes. There was a significant difference in insect abundance amongst the study sites weighted by the number of trapping hours at each study site [analysis of variance (ANOVA) F 4,18 = 3.0, P \ 0.05 and F 4,16 = 7.0, P \ 0.05 during the summer and winter, respectively).…”

“…The soils of the Knysna forests are generally acidic and nutrient poor, and compared to other forests in South Africa, plant species richness is low (Mucina and Geldenhuys 2006). Consequently, the species richness of invertebrates and of species that rely on invertebrate food, such as insectivorous birds, is relatively low in the Knysna forests (Koen and Crowe 1987). Nonetheless, the species richness of the clutter-edge functional group at KN was not significantly lower or higher than that of clutter-edge functional groups at the other study sites.…”

Importance of forest structure versus floristics to composition of avian assemblages in tropical deciduous forests of Central Highlands, India

“…In a majority of subsequent investigations on forest bird communities, vegetation composition emerged as the most significant factor (e.g., Lopez and Moro, 1997;Fleishman et al, 2003;Lee and Rotenberry, 2005). While some studies established the roles of both floristics and physiognomy as equally important in structuring avian assemblages (e.g., Arnold, 1988;Mac Nally, 1990;Bersier and Meyer, 1994), a few could not find any significant evidence for either of the components (e.g., Koen and Crowe, 1987). Such variations in avian responses have been attributed to several factors, among which the ecological scale of investigation (e.g., Wiens et al, 1987) and the food habits of birds (e.g., Cueto and de Casenave, 2000) have wide empirical support.…”

Understanding community structure: a data-driven multivariate approach

“…Studies examining the role of plant species in structuring animal communities have been similarly equivocal. These typically use species richness or diversity to summarize the plant community, and often Wnd weak (e.g., Siemann et al 1998;Parker et al 2001;Hawkins and Pausas 2004) or contradictory (Siemann 1998) relationships, or none at all (Heck and Wetstone 1977;Koen and Crowe 1987;Brose 2003). Studies using multivariate techniques to describe plant communities have generally met with greater success in detecting relationships between plant and animal communities (Rotenberry 1985;Sanderson et al 1995;Martínez-Vilalta et al 2002).…”