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Effects of woodland modification by African elephant Loxodonta africana on bird diversity in Northern Botswana
Ecography
Abstract
Bird diversity was assessed by point-transect-count sampling during the dry and the wet season in riverine gallery woodland and in Colophospermum mopane woodland with different levels of elephant impact Dramatic woodland degradation did not result in a dramatic overall reduction m bird diversity, but resulted in substantial changes in bird species composition and capacity for migrant birds Less affected, more dense woodlands functioned as dry season refuges for‘resident’Afrotropical species, but this function was lost in degraded woodlands In contrast, secondanzed habitat had a much higher capacity for long distance migrants in the wet season Species endemic to the sub-region and subspecies with restricted ranges centred in the area were not negatively affected by woodland degradation The cumulative interference of past and current elephant numbers with the conservation of bird diversity appears to be insignificant in northern Botswana
... In East Africa, it was shown that large herbivores, including elephants and giraffes, had a significant indirect effect on bird diversity via their negative effect on arthropod abundance and biomass (Ogada et al. 2008;Banks et al. 2010). Although elephant impact was found to have no effect on bird diversity in riparian woodlands in Botswana, more intact woodlands could better act as dry season refuges and were associated with many more birds than in the wet season (Herremans 1995). ...
... In riparian woodlands near Botswana's Chobe River, elephant-induced degradation of woody vegetation led to a replacement of bird species, rather than a loss of bird diversity. This suggests that patchiness in elephant disturbance could determine higher bird diversity at larger regional scales (Herremans 1995). Motsumi (2002) found that gallinaceous birds were more abundant in heavily impacted areas compared with elsewhere in the Chobe River region of Botswana. ...
... Motsumi (2002) found that gallinaceous birds were more abundant in heavily impacted areas compared with elsewhere in the Chobe River region of Botswana. Apart from browser impacts on bird communities via impacts on vegetation structure, browsers can also affect bird species by changing plant species composition (Ralph 1985;Herremans 1995;Whelan 2001). This especially occurs when fruit-bearing woody species (Willson et al. 1994), or plants that provide distinct foraging environments for insectivorous bird species, are lost due to intense browsing (Whelan 2001;Skowno and Bond 2003). ...
In this chapter we focus on the impacts of browsing and grazing ungulates on faunal biodiversity. It is not intended to be an exhaustive review of the literature, but aims to increase understanding of the extensive range of direct and indirect effects that ungulates may have on faunal diversity, and ultimately, consequences for management of systems where ungulates occur.
... In East Africa, it was shown that large herbivores, including elephants and giraffes, had a significant indirect effect on bird diversity via their negative effect on arthropod abundance and biomass (Ogada et al. 2008;Banks et al. 2010). Although elephant impact was found to have no effect on bird diversity in riparian woodlands in Botswana, more intact woodlands could better act as dry season refuges and were associated with many more birds than in the wet season (Herremans 1995). ...
... In riparian woodlands near Botswana's Chobe River, elephant-induced degradation of woody vegetation led to a replacement of bird species, rather than a loss of bird diversity. This suggests that patchiness in elephant disturbance could determine higher bird diversity at larger regional scales (Herremans 1995). Motsumi (2002) found that gallinaceous birds were more abundant in heavily impacted areas compared with elsewhere in the Chobe River region of Botswana. ...
... Motsumi (2002) found that gallinaceous birds were more abundant in heavily impacted areas compared with elsewhere in the Chobe River region of Botswana. Apart from browser impacts on bird communities via impacts on vegetation structure, browsers can also affect bird species by changing plant species composition (Ralph 1985;Herremans 1995;Whelan 2001). This especially occurs when fruit-bearing woody species (Willson et al. 1994), or plants that provide distinct foraging environments for insectivorous bird species, are lost due to intense browsing (Whelan 2001;Skowno and Bond 2003). ...
Indirect effects of browsers may ultimately influence woody: grass ratios and plant species, and thus have significant effects on the cycling and storage of key elements, such as nitrogen (N) and carbon (C) across savanna ecosystems. This chapter focuses on how indirect effects of browsers can affect other plant and animal species, ecosystem processes including C and N cycling and storage, and the frequency and intensity of wildfires. Megabrowsers can outcompete mesobrowsers for food by altering plant community structure and by creating unsuitable habitats for smaller herbivores. Changes in browse quality after defoliation are quite variable and may be related to the intensity of defoliation. Birds play an important role in woody plant regeneration through pollination and dispersal of seeds. Herbivore activities can increase herpetofaunal habitats either directly by increasing niches or indirectly by increasing habitat complexity.
... Separate studies of human and elephant disturbance suggest that while anthropogenic impacts on woody biomass and biodiversity are often negative (but see Luck 2007;Winfree et al. 2007;Andela et al. 2017 for exceptions), elephant impacts are variable, and dependent upon elephant density as well as factors such as fencing, proximity to artificial water bodies, rainfall and soil character (Guldemond and Van Aarde 2008;Guldemond et al. 2017). Furthermore, studies have demonstrated that increased elephant concentrations may reduce landscape heterogeneity through size-structured tree removal (Asner and Levick 2012), with possible effects on the landscape-wide species and functional b-diversity of faunal communities (Herremans 1995;Cumming et al. 1997). Thus, human and elephant disturbance may be associated with divergent consequences, an understanding of which is paramount for the effective management of the savanna woodlands. ...
... The open-canopied mopane woodlands provide a characteristic habitat for cavity nesting, ground foraging, and canopy-specialist birds-the woodland species (Herremans 1995). A less disturbed woodland containing trees of diverse size classes has high habitat heterogeneity and supports bird communities composed of the dominant woodland species as well as the locally infrequent non-woodland species (Herremans 1995). ...
... The open-canopied mopane woodlands provide a characteristic habitat for cavity nesting, ground foraging, and canopy-specialist birds-the woodland species (Herremans 1995). A less disturbed woodland containing trees of diverse size classes has high habitat heterogeneity and supports bird communities composed of the dominant woodland species as well as the locally infrequent non-woodland species (Herremans 1995). While, the dominant woodland species form the core of the bird community, the infrequent nonwoodland species largely determine the compositional variability-the spatial b-diversity (Socolar et al. 2016). ...
Context
Humans and elephants are major disturbance agents in the African savanna woodlands. While both species remove trees, humans selectively harvest larger stems, which are less vulnerable to elephants. Increasing human pressures raise the question of how the altered disturbance regime will modify woodland structure, and in turn biodiversity and ecosystem function.
Objectives
Here we investigate this process in the mopane woodlands of Zambia by examining relationships between woodland structure, species and functional bird diversity, and human and elephant disturbance intensity.
Methods
We conducted a single-season comparison of 178 plots from 45 sites using Bayesian mixed models.
Results
The effect of elephants on tree density (− 7.7 ± 1.6%; deviation from intercept) and bird species richness (− 15 ± 6%) was greater than that of humans (density: − 3.5 ± 1.5%; bird richness: − 11.6 ± 4.7%). Despite this, elephants did not significantly affect woody biomass or functional bird diversity, whereas humans had a negative effect on both (woody biomass: − 9.3 ± 2.3%; functional bird diversity: − 5 ± 2%). Elephants were associated with reductions in species and functional turnover (5.3 ± 2.5% and 6 ± 3%, respectively).
Conclusions
Replacement of elephants by humans is likely to reduce woody biomass and functional bird diversity affecting the woodland structure, sustainability, and functioning. Concentrated elephant disturbance could lead to spatial homogeneity in bird species and functional compositions, potentially reducing the spatial resilience of bird communities. This is the first study to highlight how the difference between elephant and human disturbances leads to dissimilar effects on biodiversity.
... Despite speculation that elephant-induced habitat modification threatens bird communities, there are only two published studies on the topic (Herremans 1995;Cumming et al. 1997). Both demonstrated that bird species with specific habitat requirements appear to be negatively influenced by elephants (Herremans 1995;Cumming et al. 1997) presumably because of reduced food supplies and increased predation risk due to altered habitat structure. ...
... Despite speculation that elephant-induced habitat modification threatens bird communities, there are only two published studies on the topic (Herremans 1995;Cumming et al. 1997). Both demonstrated that bird species with specific habitat requirements appear to be negatively influenced by elephants (Herremans 1995;Cumming et al. 1997) presumably because of reduced food supplies and increased predation risk due to altered habitat structure. However, for some bird species, reduced habitat complexity may be beneficial (Seymour and Dean 2010). ...
... Ecological responses depend on, but are not limited to, grazing/browsing intensity (Miller 1982), evolutionary history of grazing/browsing (Milchuna and Lauenroth 1993) and scale (Hill and Hamer 2004). In contrast to studies from Zimbabwe (Cumming et al. 1997) and Botswana (Herremans 1995), elephant presence did not appear to negatively affect the abundance and diversity of songbirds within Albany Thicket. In fact, my results suggest that songbird richness, density and diversity increased the longer elephants had been present at a site. ...
When vegetation structure is altered, songbird communities may be affected. Despite speculation that African Elephant (Loxodonta africana) browsing impacts bird communities, existing data are limited. I sampled the bird communities of the Albany Thicket Biome at 10 sites in the Eastern Cape, South Africa, half with elephants and half without. Songbird community parameters were best predicted by how long elephants had been present, elephant density and the percentage cover of thicket vegetation. The sites where elephants had been present for longer had more bird species and increased songbird density and diversity. However, bird density also increased with increasing thicket vegetation cover and this is a phenomenon unlikely to be compatible with long-term elephant presence. There was an almost equal split between the number of bird species that appeared to be negatively affected by changes in habitat structure (47%) and those which benefited (53%). Smaller birds were generally more abundant as vegetation structural integrity increased and larger birds were more abundant when vegetation structural integrity declined. The browsing of elephants could be viewed as facilitative for songbirds in the short term. However, this effect may not persist in the long term because all elephant populations (notorious tree-fellers) in the Eastern Cape are found in fenced areas where natural migration is not possible. More broadly, my data provide important insight into how avian communities respond to habitat transformation at the local and regional scales.
... It holds elephant numbers estimated at 11595 (~29% of CNP population) especially during the dry season exclusive of other species. The elephant is regarded as influential in habitat degradation and vegetation change (Herremans, 1995, Ben-Shahar, 1998. Therefore continued elephant presence in the Chobe river front has inevitably had an influence on the vegetation status quo. ...
... This situation is seen on the alluvial terrace adjoining the Chobe River (Owen-Smith 2006). Elephants are known for their ability to convert vegetation from woodland to shrubland and eventually to grassland over a prolonged period of time (Herremans, 1995). Opening of habitat poses an array of possibilities in an ecosystem, for instance it affords the non-dominant plant species the opportunity to colonize an area. ...
... The effects of vegetation changes caused by elephants on other wildlife species have been barely studied. A few studies have looked at the impact l. africana has had on vegetation (Rutina 2004, Herremans 1995and Ben-Shahar 1998 and even fewer have looked at the effects on other animals. Herremans (1995) studied the effects of woodland modification by elephants at high density on bird diversity at a large scale (Chobe National Park). ...
The ecological role played by elephants in African savannas has been of central concern to ecologists for decade. While elephant herbivory has been suggested to reduce biodiversity, it enhances biodiversity in some ecosystem. Elephants have been structuring woodlands along the Chobe Riverfront, changing them to shrublands. We investigated bird distribution in different habitat along the Chobe riverfront. We recorded 46 bird species, 18 of which were specific to close woodland, 2 to open woodland, 10 to shrubland and 5 common to all habitats. Bird diversity was high in closed woodland and less in shrubland. Bird diversity was high at low and medium elephant density and low at high elephant density. Baikiaea woodland had the highest diversity index, followed by mixed woodland; mixed shrubland and riparian woodland in descending order. Elephant density (20.97 elephants/square kilometer) was higher in mixed shrublands, followed by riparian woodland (10.51 elephants per square kilometer), mixed woodland (8.1 elephants per square kilometer) and Baikiaea woodland had the least elephant representation, with 3.34 elephants per square kilometer. There was a negative correlation between elephant densities and avian diversity (P < 0.05). The results suggest that although elephants have been reported to facilitate populations of herbivores in Chobe riverfront, it might have negative influence in avian diversity. Further studies to assess the influence of elephant herbivory on avian guild structure are recommended.
... In contrast, Herremans (1995), assessing bird community species shifts in riverine forest and Mopane woodland in northern Botswana, found that dramatic woodland change associated with the high abundance of elephants did not result in a reduction in bird diversity. This was possibly due to the fact Effects of elephants on ecosystems and biodiversity that woodland conversion was spatially restricted. ...
... Both small mammals and gallinaceous birds (guinea fowl and spur fowl) appeared more abundant in places that had incurred severe elephant impacts. The Chobe River front retained an exceptionally high density of land birds, especially of migrants (Herremans, 1995). Nevertheless, the opening of the woody vegetation cover by elephants was associated with a substantial reduction in the abundance of bushbuck, to a third or less of their former abundance (Addy, 1993). ...
... In contrast, Herremans (1995), assessing bird community species shifts in riverine forest and Mopane woodland in northern Botswana, found that dramatic woodland change associated with the high abundance of elephants did not result in a reduction in bird diversity. This was possibly due to the fact Effects of elephants on ecosystems and biodiversity that woodland conversion was spatially restricted. ...
... Both small mammals and gallinaceous birds (guinea fowl and spur fowl) appeared more abundant in places that had incurred severe elephant impacts. The Chobe River front retained an exceptionally high density of land birds, especially of migrants (Herremans, 1995). Nevertheless, the opening of the woody vegetation cover by elephants was associated with a substantial reduction in the abundance of bushbuck, to a third or less of their former abundance (Addy, 1993). ...
... Previous studies have consistently shown that these disturbances include, among others, climate extremes Bond, 2015, Scheiter andSavadogo, 2016), veld fires (Staver et al., 2017, Luvuno et al., 2016 and foraging by mega-herbivores like the African elephant (Bakker et al., 2016. For instance, ecologists generally agree that elephants change their own habitats as well as that of other animal species when foraging (Pringle et al., 2015, Herremans, 1995. Thus, change in vegetation structure driven by elephant foraging is a key topic in ecological disturbance theory. ...
... Thus, it can be hypothesised that in a heterogeneous savannah landscape, selective use of vegetation/cover type by elephants translates to differential impact on vegetation structure and that change can be conceptualised ( Figure 6-1). Overall, understanding where vegetation change occurs in the landscape and to what extent is critical because the change often alters the use of the landscape by other wildlife species (Herremans, 1995, Valeix et al., 2011. For instance, change in structure from woodland to grassland could result in the landscape being used more by grassland species than woodland species. ...
Knowledge of elephant (Loxodonta africana) impact on vegetation is critical for conservation of the mega-herbivore and of other wildlife species found in the ecosystem. Although the impact of elephants on vegetation structure has been investigated before, location and time specific knowledge on changes in the landscape has remained largely inconclusive. This is because most of the early studies largely depended on plot-based observations that are limited in scope both spatially and temporally. This thesis develops and applies GIS and remote sensing methods aimed at understanding the spatial pattern of elephant- impact on vegetation interaction in a predominantly savannah landscape. Specific objectives of the study were to: (1) understand the predictive ability of elephant distribution models developed using presence data collected from GPS collars and compare them to those developed from aerial survey data; (2) develop and test new methods for correcting locational error in aerial survey data for improving models of elephant distribution; (3) test whether elephant presence peaks farther from water points in addition to the known peak near water; (4) investigate whether elephants selectively utilise a heterogeneous landscape; and (5) test whether and how the rate of change in vegetation structure differs across a heterogeneous landscape. Firstly, results show that elephant presence models built from GPS collar data outperformed those built from aerial survey data. Secondly, the method suggested for correcting error in aerial survey data shifted location by 143 to 177m from the line of flight. In addition, the models of elephant presence built from the corrected dataset had better predictive ability than those built from uncorrected data. Thirdly, elephant presence peaked at places located farther from water sources in addition to the known peak near water. The peaks occurred in areas of high vegetation cover.
Fourthly, elephant speed of movement and utilisation of the landscape (i.e., speed, Linear Time Density and the Kernel Density Estimator) differed by vegetation/cover type. Fifthly, the rate of tree cover change differed by vegetation/cover type. The change was also observed to be correlated with elephant movement and utilisation of the landscape. Results of the thesis thus suggest that GIS and Remote sensing- based methods improve our understanding of elephant-vegetation dynamics distribution in the landscape in space and time. These findings underscore the utility of GIS and remote sensing in studies that investigate the spatial pattern of elephant interaction with impact on vegetation. Knowledge of those patterns could be applied in the formulation of strategies aimed at conserving the African elephant as well as other wildlife species that co-occur with the megaherbivore
... The sites of intermediate or high levels of herbivore presence in our study in Botswana were consistently associated with higher avian richness and diversity at species and functional group levels (Fig. 3). This is supported by other evidence that large African herbivores are functional drivers of ecosystems (Ogada et al. 2008;Banks et al. 2010), including within Botswana (Herremans 1995). The higher diversity and richness of 11 avian functional groups at sites with medium or high levels of herbivore presence were likely due to a mix of direct effects and indirect benefits provided by large herbivores. ...
... The higher diversity and richness of 11 avian functional groups at sites with medium or high levels of herbivore presence were likely due to a mix of direct effects and indirect benefits provided by large herbivores. These include variation in vegetation condition, structure, dispersal and germination (Herremans 1995;Campos-Arceiz and Blake 2011;Baker et al. 2016), faeces and urine deposition (van der Waal et al. 2011), and the creation of opportunities for other species including frogs (Nasseri et al. 2011), small herbivorous mammals (Valeix et al. 2011) andbirds (Banks et al. 2010), increasing food availability for the avian community. ...
Large herbivores directly and indirectly influence ecosystem function, positively and negatively affecting diversity of plants and animals, including birds. Such cascading effects are clearly important, particularly given ongoing global declines in large herbivores and many avian communities. We examined relationships between bird diversity (species richness and Shannon-Weiner Index, at a species and functional group level) at three similarly vegetated and flooded sites in northern Botswana. We explored the role that herbivore presence plays in ecosystem functioning considering bird species richness was significantly higher at the site of intermediate presence, followed by the high presence site. At a functional group level, the site of highest presence consistently had the greatest functional group richness. Also, at a functional group level we identified higher species richness and diversity in the two sites where herbivores were present at high levels. This was particularly pronounced for the avian aquatic carnivore, terrestrial herbivore, and aerial invertivore functional groupings. Large herbivores probably increased habitat complexity through their browsing and grazing, altering habitat structure, alongside other benefits such as faeces deposition and mutualistic relationships, creating more niches for avian communities. Fencing out large herbivores to reduce their grazing and browsing may therefore reduce bird diversity, and correspondingly, allowing large herbivores to increase in abundance through protected areas may indirectly increase bird diversity, acknowledging over abundance may be detrimental.
... He raised concerns about the depletion of other wildlife in Tsavo National Park, Kenya, through elephant impacts. Barnes (1983) stated that major changes in woody vegetation density will have important implications for birds, and Hall- Martin (1990) claimed drastic reductions in bird diversities due to elephant activities in Tsavo, but as noticed by Herremans (1995) no evidence supported it. Nothing was known about elephant impact on animal communities that elephants were already labelled as agents of diversity loss... Is it the case? ...
... 2.1.1 On various taxa Herremans (1995) observed a change in the bird community composition correlated to elephant impacts on vegetation in Chobe National Park, Botswana, but did not reveal a drastic loss in bird species diversity. Further, Stokke et al. (2014), showed in the same park a positive correlation between gallinaceous bird diversity and long-term elephant impact. ...
Species can indirectly affect other species and their interactions. The trophic interaction between a predator and its prey can be modified by the presence of a third species either through chain interactions (e.g. successive predation link) either through interaction modification. However, these indirect received few attentions in theorical modelling of food web, and fewer studies tried to explore this phenomenon at the scale of natural complex communities of large mammals. The role of the elephants as modifier of lion’s trophic interaction is explored in the semi-arid woodland savannah ecosystem of Hwange National Park, Zimbabwe. African elephants, as key competitor (male body mass ~ 4000 kg with aggressive behaviour) shape the behaviour of herbivores at waterholes results do not allow to state on the elephant mediation of lion trophic interaction at waterholes. In addition, elephants seem to facilitate the availability of food resources for impalas, possibly by increasing regrowth of shoots by breaking twigs and stem, as these last select habitats used by elephants. However, not effect of facilitation or competition were observed for the other herbivores, which lead to think that elephants do not influence lion trophic interaction in that way. Finally, by altering the physical environment (i.e. engineer species) the elephants affect the visibility and ambush sites for lions in the woody vegetation and ultimately seem to influence the lion kill site selection. This study suggests that indirect effects may act at the community level even if their observation and quantification are difficult in natural communities. Moreover, it supports the observation that it is important to take into account these indirect effects in order to have a thorough understanding and have a better ability to predict the consequences that disruptions may have on the structure and functioning of communities
... Our area of interest was Chobe National Park, Botswana (lat 18.5 S, long 24.5 E). The park has robust and increasing elephant populations (50,000– 80,000; Nellis et al. 1990; Ben-Shahar 1993; Herremans 1995) that damage Zambezi teak ( Balklaiea plurijuga ) and associated forest species. The negative effects of expanding elephant populations on woodland vegetation are of concern (e.g., Ben-Shahar 1993 Herremans 1995), particularly to local land managers and national conservation planners seeking a sustainable balance between wildlife populations and natural vege- tation. ...
... The park has robust and increasing elephant populations (50,000– 80,000; Nellis et al. 1990; Ben-Shahar 1993; Herremans 1995) that damage Zambezi teak ( Balklaiea plurijuga ) and associated forest species. The negative effects of expanding elephant populations on woodland vegetation are of concern (e.g., Ben-Shahar 1993 Herremans 1995), particularly to local land managers and national conservation planners seeking a sustainable balance between wildlife populations and natural vege- tation. After a search of the database of astronaut photography of Earth, we selected one photograph to demonstrate the use of this imagery in the detection of vegetation stress (NASA photograph STS008–33–993; Fig. 2, left). ...
The work of conservation biology has grown from local studies of single species into a discipline concerned with mapping and managing biodiversity on a global scale. Remote sensing, using satellite and aerial imaging to measure and map the environment, increasingly provides a vital tool for effective collection of the information needed to research and set policy for conservation priorities. The perceived complexities of remotely sensed data and analyses have tended to discourage scientists and managers from using this valuable resource. This text focuses on making remote sensing tools accessible to a larger audience of non-specialists, highlighting strengths and limitations while emphasizing the ways that remotely sensed data can be captured and used, especially for evaluating human impacts on ecological systems.
... Understanding the woody vegetation dynamic of the savanna ecosystem, which is mainly driven by the complex interaction of factors such as elephants and fire, is of crucial importance due to its cascading effects on many other biological components, such as birds, bats, mantises, and ants (Cumming et al. 1997;Fenton et al. 1998;Herremans 1995;Johnson et al. 1999;Lombard et al. 2001;Owen-Smith et al. 2006). GNP is characterized by at least a decade of high elephant density and has experienced intense fires over the past two decades. ...
Aims
This study assessed changes in woody vegetation cover, richness, diversity, and species composition in Gonarezhou National Park (GNP) between 2010 and 2023, focusing on the impacts of fire and elephants. Analyses were conducted for the entire park and its main vegetation types and ecoregions.
Location
GNP is located in southern Zimbabwe, bordering Mozambique, covering approximately 5000 km ² .
Methods
In 2010, 313 sampling areas were surveyed, and a resurvey was conducted in 2022/2023 using a plotless method. For each area, woody species cover was recorded in four height classes. Indices for total woody cover, species richness, diversity (Shannon), and evenness (Pielou) were calculated for both surveys across the park, ecoregions, and vegetation types. Differences between surveys were analyzed with paired t‐tests. Species composition changes were analyzed using NMDS and PERMANOVA, while the effects of fire frequency, slope, and distance from rivers on species composition were tested with a mixed linear model. The change in dominant species occurrence was also examined.
Results
Species richness significantly declined, with no changes in woody vegetation cover, diversity, or evenness, except in the alluvial ecoregion, where diversity decreased. Changes across height layers revealed increased richness and diversity in the < 1 m layer and declines in the 1–3 m and 3–5 m layers. Species composition changes were significant across ecoregions and influenced by fire frequency. A decrease in dominant tree species was observed, varying by species' resilience to current pressures.
Conclusions
GNP is undergoing simplification in woody vegetation, likely due to the combined effects of elephants and fire. This is leading to shrubbier vegetation and changes in species composition, particularly in trees. To prevent further degradation, actions must be implemented, such as the use of individual protection systems from debarking, the development of a fire management system, and the creation of ecological corridors in the Greater Limpopo Transfrontier Conservation Area to facilitate the movement of elephants.
... To date, only a limited number of studies have examined the effects of high levels of EHD on other wildlife species, with the majority focusing solely on herpetofauna and small bird species. While herpetofauna exhibited increased diversity and richness in areas with high EHD, passerines and other small avian species responded inversely and exhibited decreased levels of diversity, richness, and abundance in areas that had undergone high levels of EHD (Herremans 1995;Pringle 2008;Ogada et al. 2008;Nasseri et al. 2011;Vogel et al. 2014). The few studies conducted on the impacts of EHD on large birds and mammals have mostly focused on a single charismatic species, such as lions (Panthera leo) and vultures, omitting data on community dynamics (Fritz et al. 2002;Valeix et al. 2011;de Boer et al. 2015;Fležar et al. 2019;Ferry et al. 2020). ...
... As such, the effects that elephants have on the habitats they occupy have been explored for decades (see for example Beuchner and Dawkins 1961;Glover 1963;Laws 1970;Field 1971;Anderson and Walker 1974;Caughley 1976;Cumming et al. 1997;O'Connor et al. 2007). Elephants can have an extensive influence (both positive and negative) on local biodiversity (Kerley and Landman 2006) through processes such as tree mortality (toppling, pollarding, ringbarking;O'Connor et al. 2007), habitat modification for other organisms (Laws 1970;Herremans 1995;Pringle 2008;Fritz 2017), seed dispersal (Campos-Arceiz and Blake 2011; Beaune et al. 2013;Bunney et al. 2017), and predator access and predation risk (Tambling et al. 2013;Fležar et al. 2019). Elephants alter both the compositional and structural diversity of vegetation, ultimately affecting functional species biodiversity as well, across a range of scales from the population-species level up to the regional-landscape level Mapaure and Moe 2009;Rutina and Moe 2014). ...
Heterogeneity, the spatio-temporal variation of abiotic and biotic factors, is a key concept that underpins many ecological phenomena and promotes biodiversity. Ecosystem engineers, such as African savanna elephants (hereafter elephant), Loxodonta africana, are organisms capable of affecting heterogeneity through the creation or modification of habitats. Thus, their impacts can have important consequences for ecosystem biodiversity, both positive and negative. Caughley’s “elephant problem” cautions that confined or compressed, growing elephant populations will inevitably lead to a loss of biodiversity. However, a shift in our understanding of elephants suggests that not all elephant impacts lead to negative biodiversity consequences, as long as there is a heterogeneous spread of elephant impacts that allows for spatio-temporal refuges promoting the persistence of both impact-tolerant and impact-intolerant species. To date, little empirical evidence is available in support of managing elephants under this paradigm and few studies are available that infer the consequences of the distribution of elephant impacts on biodiversity. In addition, most studies use parametric statistics that do not account for scale, spatial autocorrelation, or non-stationarity, leading to a misrepresentation of the underlying processes and patterns of drivers of elephant space-use and the consequences of their impacts on biodiversity. Here, I evaluate spatio-temporal patterns and drivers of elephant space-use, and how the distribution of their impacts affects biodiversity through vegetation changes, using a multi-scaled spatial approach, in Liwonde National Park, Malawi. My study demonstrates that elephant space-use in Liwonde is heterogeneous, leading to spatio-temporal variation in the distribution of their impacts, even in a small, fenced reserve. The importance of the drivers of this heterogeneous space-use varied based on the scale of analysis, water was generally important at larger scales while vegetation quality (indexed by NDVI) was more important at smaller scales. When examined using local models, my results suggest that relationships exhibit non-stationarity, what is important in one area of the park is not necessarily important in other areas. The spatio-temporal variation of the inferred impacts of elephants in Liwonde still allowed for spatio-temporal refuges to be created, no clear linear relationship was found between elephant return intervals and woody species structural and functional diversity (indexed by changes in tree cover and changes in annual regrowth using Normalized Difference Vegetation Index as a measure, respectively) throughout the park. My study provides support for adopting the heterogeneity paradigm for managing elephants and demonstrates that not all elephant impacts result in negative vegetation change. I also demonstrate the crucial implications of accounting for scale, non-stationarity, and spatial autocorrelation to evaluate how animals both respond to, and contribute to, environmental heterogeneity.
... Our results suggest that the elephants' pastures are not completely unsuitable for Mount Cameroon forest birds, as the environmental changes caused by elephants were not so profound as to cause the loss of a bird community, as was found by other studies, e.g., [24]. Moreover, Herremans [29], supported the evidence that more species of birds inhabited open landscape as opposed to less affected areas. Although increased vegetation heterogeneity or floristic diversity of a given habitat does not always lead to increased species diversity [63,64], the vast majority of studies show that heterogeneity of vegetation supports increased diversity of animals [65,66]. ...
Most of the tropical rainforests are subject to both anthropogenic and natural disturbances. Forest elephants (Loxodonta cyclotis) cause forest clearings within the tropics. This study was conducted at mid-elevations (1100–1700 m a.s.l.) in Mount Cameroon National Park. We assessed the difference in the structure of bird communities in the forest and areas located nearby affected by elephant activities. We used the point-count method; 22 points were established within each habitat. The vegetation was visually estimated within a 50 m radius surrounding each counting point. In total, 1603 birds from 85 species were recorded. The vegetation cover from 3 to 5 m at points with elephant activity was significantly lower compared to points without elephant activity. Bird species richness was significantly higher around points in pasture compared to points in intact forest. Habitat type and the percentage of vegetation layer from 3 to 5 m significantly impacted the bird community structure. The points in the pasture were especially characterized by the increased abundance of some open habitat species (e.g., Chubb’s Cisticola chubbi). Few studies have documented the effects of elephant activity on other species, although the effects are widely stated as important drivers of habitat diversity in tropical forests. In conclusion, disturbance caused by elephants leads to increased bird community diversity due to the increased heterogeneity of the environment, which documents the high importance of elephants as ecosystem engineers.
... Our results extend on previous research on the link between animal behaviour and land cover taking a step further (Herremans 1995;Da Silveira et al., 2016;Brown et al. 2017). As first proposed by Weinzierl et al. (2016) in the field of atmospheric simulation, our study suggests animals are useful sensors and we showed they can also provide valuable ground-truth data for remote sensingbased land cover classification. ...
Land cover is a key variable in monitoring applications and new processing technologies made deriving this information easier. Yet, classification algorithms remain dependent on samples collected on the field and field campaigns are limited by financial, infrastructural and political boundaries. Here, animal tracking data could be an asset. Looking at the land cover dependencies of animal behaviour, we can obtain land cover samples over places that are difficult to access. Following this premise, we evaluated the potential of animal movement data to map land cover. Specifically, we used 13 White Storks (Cicona cicona) individuals of the same population to map agriculture within three test regions distributed along their migratory track. The White Stork has adapted to foraging over agricultural lands, making it an ideal source of samples to map this land use. We applied a presence–absence modelling approach over a Normalized Difference Vegetation Index (NDVI) time series and validated our classifications, with high‐resolution land cover information. Our results suggest White Stork movement is useful to map agriculture, however, we identified some limitations. We achieved high accuracies (F1‐scores > 0.8) for two test regions, but observed poor results over one region. This can be explained by differences in land management practices. The animals preferred agriculture in every test region, but our data showed a biased distribution of training samples between irrigated and non‐irrigated land. When both options occurred, the animals disregarded non‐irrigated land leading to its misclassification as non‐agriculture. Additionally, we found difference between the GPS observation dates and the harvest times for non‐irrigated crops. Given the White Stork takes advantage of managed land to search for prey, the inactivity of these fields was the likely culprit of their underrepresentation. Including more species attracted to agriculture – with other land‐use dependencies and observation times – can contribute to better results in similar applications. Land cover is a key variable in monitoring applications and new processing technologies made deriving this information easier. Here, we evaluated the potential of animal movement data to map land cover. Specifically, we used 13 White Storks (Cicona cicona) individuals of the same population to map agriculture within three test regions distributed along their migratory track. We applied a presence–absence modelling approach over a Normalized Difference Vegetation Index (NDVI) time‐series and validated our classifications, with high‐resolution land cover information. Our results suggest White Stork movement is useful to map agriculture, but we identified some limitations. Including more species attracted to agriculture – with other land‐use dependencies and observation times – can contribute to better results in similar applications.
... In contrast, browsing mammals reduce canopy and so reduce diversity and species composition (Ogada et al. 2008). In some cases, species composition but not diversity changed with browsing (Herremans 1995;Caston and Samantha 2014), which underlines the point that diversity may not be the best metric for measuring impacts on biotic communities and measures of species composition, richness and similarity are more meaningful. ...
Context
The increase in density of large tree species, Vachellia robusta and V. tortilis, in the Serengeti Ecosystem of Tanzania has resulted in a decline of small tree species Senegalia senegal, V. hockii, Commiphora spp. This change has occurred since the late 1970s, a consequence of an increase in wildebeest following the extirpation of rinderpest, which reduced the dry grass fuel for fires, resulting in low fire frequencies. Change in tree species raises the question of whether there are indirect consequences for the avifauna that depend on the large trees for food and nesting.
Aims
To determine how an increase in large mammals could influence diversity and distribution of avifauna communities in the Serengeti ecosystem woodlands.
Methods
Data used to estimate changes in density of large and small trees were measured by Point Centre Quarter (PCQ). Bird species were recorded in 19 small-tree sites and 18 large-tree sites in the Serengeti National Park. Richness of bird guilds was calculated in the two habitat complexes (small and large trees), and the ‘rarefaction’ method was used to assess the difference in richness in habitats of the study area. Mean abundance for each species was calculated over the total number of sites for each habitat and compared using the Wilcoxon Rank Sum test to examine how the abundance of avifauna changes with each habitat type.
Key results
There was an increase in the density of large trees in some areas in which they have replaced the original small trees. Such changes have resulted in greater richness of hole nesters and bark feeders, and a greater abundance of large-hole nesters and gleaner bird species.
Conclusions
Because the increase in tree density was caused by an increase in large mammals, we conclude that this increasing mammal population is indirectly increasing richness and abundance of birds using the trees.
Implications
Understanding the influence of large mammal populations on bird distributions has important conservation implications because the Serengeti ecosystem is classified as an important, endemic bird area.
... (1) The publication included key terms and phrases about the threat categories but was not relevant to this review (e.g. 'Effects of woodland modification by African elephant (Loxodonta africana) on bird diversity in northern Botswana' (Herremans, 1995)). ...
Dryland forests provide essential resources critical to the survival of human and animal populations. They are particularly important in developing countries where community livelihoods are often directly dependent upon the use of natural resources in these habitats. In Botswana, as elsewhere in Africa, dryland forests are under increasing pressure with concomitant degradation in ecosystem services. Active management is constrained by a limited understanding of ongoing threats to dryland forest resources. Using key search terms, we conducted a systematic review of published literature in order to evaluate research trends, resource threats and knowledge gaps in respect of dryland forest resources occurring in Botswana and the Southern African region. Of the 221 publications identified (1974-2016), fire and elephant research dominate the scientific literature (58%), often in combination with each other (11%).While other threats are noted and considered important (agriculture, climate change, commercial harvesting, disease and pests, exotic invasive species and human encroachment), there remains a paucity of research on these topics. These data suggest that there is an urgent need to expand the research agenda in the forest sector prioritizing other threat types rather than continued focus on elephants and fire.
... High densities of large wild mammals, which substantially affect vegetation structure and composition (Sankaran, Augustine, & Ratnam, 2013), characterize savannas in Africa. In Kenya, Ogada, Gadd, Ostfeld, Young, and Keesing (2008) documented a 30% increase in bird diversity in plots from which large mammals were excluded, and in southern Africa, intensive browsing by elephant (Loxodonta africana) reduced bird species abundance and diversity (Cumming et al., 1997;Herremans, 1995). We know of no studies that have attempted to disentangle the combined effects of large ungulates and termites on savanna bird abundance, richness, and diversity. ...
Vast areas of the African savanna landscapes are characterized by tree-covered Macrotermes termite mounds embedded within a relatively open savanna matrix. In concert with termites, large herbivores are important determinants of savanna woody vegetation cover. The relative cover of woody species has considerable effects on savanna function. Despite the potentially important ecological relationships between termite mounds, woody plants, large herbivores, and birds, these associations have previously received surprisingly little attention. We experimentally studied the effects of termites and large herbivores on the avian community in Lake Mburo National Park, Uganda, where woody vegetation is essentially limited to termite mounds. Our experiment comprised of four treatments in nine replicates; unfenced termite mounds, fenced mounds (excluding large mammals), unfenced adjacent savanna, and fenced savanna. We recorded species identity, abundance, and behavior of all birds observed on these plots over a two-month period, from late dry until wet season. Birds used termite mounds almost exclusively, with only 3.5% of observations occurring in the treeless intermound savanna matrix. Mean abundance and species richness of birds doubled on fenced (large herbivores excluded) compared to unfenced mounds. Feeding behavior increased when large mammals were excluded from mounds, both in absolute number of observed individuals, and relative to other behaviors. This study documents the fundamental positive impact of Macrotermes termites on bird abundance and diversity in an African savanna. Birds play crucial functional roles in savanna ecosystems, for example, by dispersing fruits or regulating herbivorous insect populations. Thus, the role of birds in savanna dynamics depends on the distribution and abundance of termite mounds.
... Botswana still has a diversity of vulture species in the wild (Hancock and Welersby 2016) and all are listed as globally threatened by the Wildlife Conservation and National Parks, Act of 1992. However, vultures have been reported to be significantly declining in unprotected areas in Botswana due to many factors including drought (Herremans 2004), land use change (Herremans & Herremans-Tonnoeyr 2000), and elephant habitat modification (Herremans 1995). Recently there have been recorded cases of vulture mortalities at wildlife and livestock carcasses in Northern Botswana (Figure 1). ...
Agrochemicals are widely used across the world to serve different purposes. However, inappropriate
use of agrochemicals affects wildlife particularly non-target species such as vultures. In this paper, we
discuss the potential threats posed by inappropriate use of agrochemicals to vultures in Botswana. We
discuss the ecosystem services provided by vultures, recent incidents of potential vulture poising in
Botswana, why vultures are vulnerable to agrochemical poisoning and status of the use of chemicals in
Botswana. We show that incidents of vulture mortalities possible due to deliberate and accidental poisoning
of livestock and wildlife carcasses by farmers and poachers, respectively, are increasing since
2009 in Botswana. In Botswana, the distribution of agrochemicals is not well regulated although the
Agrochemicals Act of 1999 and subsidiary 2003 legislation are in place to assist in this endeavour. In
addition, factors contributing to vulture declines are not well documented and researched. The lack of
information on factors contributing to vulture poisoning calls for collaborate multidisciplinary research
to assess vulture population dynamics and the drivers of their population change, including poisoning
to inform policies on use of agro-chemicals in Botswana
... Savanna elephants (Loxodonta africana) harvest food from all these plant types (Barnes, 1982;Field, 1971;Kabigumila, 1993), but their conspicuous impact on woody plants has the greatest potential to cause long-term vegetation change (Lamprey et al., 1967;Laws, 1970b;Leuthold, 1977). Over time, this behaviour may simplify the structure and composition of woodlands (O'Connor & Page, 2014), jeopardising the persistence of impacted species (Lombard et al., 2001;O'Connor, Goodman & Clegg, 2007) and the biota that are dependent on the original complexity (Cumming et al., 1997;Herremans, 1995;Kerley & Landman, 2006). Extensive impact on woodlands by elephants was first noticed in the 1930s (Laws, 1970a) and since then many wooded areas in Africa have been converted to shrubland or grassland (Spinage, 1994). ...
Loss of biodiversity caused by impact of elephants ( Loxodonta africana ) on African woodlands may require a management response, but any action should be based on an understanding of why elephants choose to utilise trees destructively. Comprehension of elephant feeding behaviour requires consideration of the relative value of the plant groups they may potentially consume. Profitability of available food is partly determined by the time to locate a food patch and, therefore, as a foundation for understanding the influence of food availability on diet selection, key controls on the density of grass, forb, and browse patches were investigated across space and time in a semi-arid African savanna. Density of food patches changed seasonally because plant life-forms required different volumes of soil water to produce green forage; and woody plants and forbs responded to long-term changes in soil moisture, while grasses responded to short-term moisture pulses. Soil texture, structure of woody vegetation and fire added further complexity by altering the soil water thresholds required for production of green forage. Interpolating between regularly-timed, ground-based measurements of food density by using modelled soil water as the predictor in regression equations may be a feasible method of quantifying food available to elephants in complex savanna environments.
... Although elephants harvest food from a range of plant life forms, it is their conspicuous impact on woodlands that has the greatest potential to cause long-term vegetation change (Lamprey et al., 1967;Laws, 1970;Leuthold, 1977;Morrison, Holdo & Anderson, 2016). Extensive conversion of woodlands to shrubland by elephants (Spinage, 1994) and the potential associated loss of biodiversity (Cumming et al., 1997;Herremans, 1995;Kerley & Landman, 2006) may require management intervention (O'Connor, Goodman & Clegg, 2007), but any action should be based on an ...
As a foundation for understanding the diet of African savanna elephants ( Loxodonta africana ), adult bulls and cows were observed over an annual cycle to determine whether harvesting ( P t ), chewing ( C t ) and handling times ( H t ) differed across food types and harvesting methods (handling time is defined as the time to harvest, chew and swallow a trunkload of food). Bulls and cows were observed 105 and 26 times, respectively (94 and 26 individuals), with a total of 64 h of feeding recorded across 32 vegetation types. Some food types took longer to harvest and chew than others, which may influence intake rate and affect choice of diet. The method used to gather a trunkload of food had a significant effect on harvesting time, with simple foraging actions being comparatively rapid and more difficult tasks taking longer. Handling time was constrained by chewing for bulls, except for the processing of roots from woody plants, which was limited by harvesting. Time to gather a trunkload had a greater influence on handling time for cows compared to bulls. Harvesting and handling times were longer for bulls than cows, with the sexes adopting foraging behaviors that best suited their energy requirements.
... In many protected areas in southern Africa, elephant populations are increasing, re-establishing former densities (Lewin, 1986;Skarpe et al., 2004) or in some cases overpopulating confined protected areas (Cumming et al., 1997;Child, 2004). In many of these areas, elephants are important agents of ecosystem change, profoundly influencing plant and animal communities (Herremans, 1995;Cumming et al., 1997;van de Koppel and Prins, 1998;Fritz et al., 2002;Chapters 4, 14 and 15). Reviewing the trophic-guild structure of ungulate communities in southern and eastern Africa, Fritz et al. (2002) found a negative correlation between the metabolic biomass density of elephants and that of ungulate browsers and mixed feeders, but no relationship with grazers, and suggested that elephants compete with browsers and mixed feeders but might facilitate grazers (Owen-Smith, 1988). ...
This chapter explores whether species in the grazing and browsing guilds respond differently to ecosystem changes induced by elephant. The target area is the northernmost part of the Chobe National Park. The chapter discusses food and habitat use by some grazers and browsers in relation to elephant impact and ecosystem type, distinguishing between the relatively nutrient-rich savannas on alluvial soil and the nutrient-poor woodlands on sand. In the chapter, preferential browsers are referred as browsers and preferential grazers as grazers; only impala and elephant are considered to be mixed feeders. The dynamics of the ungulate community has potentially been influenced by several factors, including the effects of changes in the elephant population. The chapter presents specific information on some of the species in the area.
... Wood harvesting changes not only biomass, but also vertical stratification of vegetation. Vertical vegetation complexity has relevance to ecosystem function as canopy height is related to biomass and productivity [40], biodiversity [41][42][43] and contributes to structural heterogeneity [44]. We submit that a method of understanding and, potentially, improving biomass change estimations, is to examine the vertical vegetation structure. ...
Woody biomass dynamics are an expression of ecosystem function, yet biomass estimates do not provide information on the spatial distribution of woody vegetation within the vertical vegetation subcanopy. We demonstrate the ability of airborne light detection and ranging (LiDAR) to measure aboveground biomass and subcanopy structure, as an explanatory tool to unravel vegetation dynamics in structurally heterogeneous landscapes. We sampled three communal rangelands in Bushbuckridge, South Africa, utilised by rural communities for fuelwood harvesting. Woody biomass estimates ranged between 9 Mg ha(-1) on gabbro geology sites to 27 Mg ha(-1) on granitic geology sites. Despite predictions of woodland depletion due to unsustainable fuelwood extraction in previous studies, biomass in all the communal rangelands increased between 2008 and 2012. Annual biomass productivity estimates (10-14% p.a.) were higher than previous estimates of 4% and likely a significant contributor to the previous underestimations of modelled biomass supply. We show that biomass increases are attributable to growth of vegetation
... Wood harvesting changes not only biomass, but also vertical stratification of vegetation. Vertical vegetation complexity has relevance to ecosystem function as canopy height is related to biomass and productivity [40], biodiversity [41][42][43] and contributes to structural heterogeneity [44]. We submit that a method of understanding and, potentially, improving biomass change estimations, is to examine the vertical vegetation structure. ...
... De rarefactionstatistiek is al 30 jaar in omloop en de berekening wordt aangeboden in een aantal statistische pakketten. Het is jammer dat deze bovendien visueel bevattelijke methode om diversiteit objectief te bepalen zo moeilijk ingang blijkt te vinden.Voor mij persoonlijk heeft ze al een nuttige staat van dienst voor uiteenlopende situaties, bijvoorbeeld bij vergelijking van de impact van olifanten op de vogeldiversiteit in galerijbossen(Herremans 1995), van de rijkdom en waarde van verschillende types wetlands voor watervogels in de Kalahari(Herremans 1999), van de impact van droogte op de samenstelling van vogelgemeenschappen in de Kalahari(Herremans 2004), van verschillen tussen plaatsen en seizoenen bij trekvogels in de Sahara(Herremans & Verbeeck 2005a,b) en van de invloed van het landschap op de zichtbare vogeltrek in Vlaanderen(Herremans 2005). Vooral soortenrijke groepen die relatief even-wichtig en gestandaardiseerd te bemonsteren zijn zoals bijvoorbeeld nachtvlinders, loopkevers, spinnen, paddenstoelen en (zweef)vliegen, zijn bijzonder geschikt om via rarefactionprofielen de biodiversiteit van gemeenschappen te vergelijken.Op de Vlaamse telgegevens van ondermeer overwinterende watervogels, algemene broedvogels (ABV) en de vlinderroutes, zou rarefaction bijvoorbeeld kunnen toegepast worden om de toestand of erosie van biodiversiteit omvattend te vergelijken in tijd of ruimte, of tussen habitattypes. ...
HERREMANS M. 2008. Measuring biodiversity: only counting the trees?
An attempt to include the forest.Natuur.focus 7(2):60-67.[in Dutch]
The objectives of countdown 2010 are straightforward and easy to understand, yet difficult to translate into quantitative operational targets. Indeed, no such targets are used in policy in Flanders. The distance-to-target is unknown and so is the progress (if any).This is at least in part due to the difficulties of measuring biodiversity comprehensively. Consequently, so far we seem primarily occupied by measuring what is done for biodiversity rather than what effect this all has on biodiversity. The limited data available, however, suggest
that over the last 25 years about one third of all living creatures might have disappeared from Flanders. Therefore, the situation is fairly critical. Biodiversity studies mostly focus on species richness, which is, however, very sensitive to search effort. Indicator species are another popular way to assess biodiversity, but only few suitable indicators have been identified for specific habitats in Flanders so far.
In this paper I suggest to measure biodiversity also at the community level, taking into account the abundance structure in the community. The rarefaction algorithm allows to do so, and furthermore, is the appropriate method to compare samples of different size (which is a frequent problem in nature research). Rarefaction translates community structure biodiversity into ‘the chance that the next individual found belongs to a different species’.It allows to draw a curve expressing expected species diversity in samples of various
sizes. Several examples are given to demonstrate the possibilities of the method is assessing a community measure of biodiversity.This measure is furthermore sensitive to early disturbance in the community,
while measuring species diversity has to wait until extinct species eventually show up in the statistics.
... Unfortunately, Baobab trees are being damaged by local people in the southeast Lowveld, through fibre extraction/removal from tree trunks to make mats for sale to tourist, and also as fibre for the construction of dagga huts. Elephants in our national parks bring down and destroy many Baobab trees to feed on the fibre, because of the lack of foliage for the ever-increasing elephant population during drought years (Herremans 1995). Many other large trees are being claimed for dugout canoes in the Zambezi Valley, while virgin forests, most of them Mopane Woodland, are also being cleared to make way for crop cultivation, especially in Zimbabwe's Agricultural Regions 1-3, mainly in Mashonaland, where tobacco is heavily cultivated. ...
... Unfortunately, Baobab trees are being damaged by local people in the southeast Lowveld, through fibre extraction/removal from tree trunks to make mats for sale to tourist, and also as fibre for the construction of dagga huts. Elephants in our national parks bring down and destroy many Baobab trees to feed on the fibre, because of the lack of foliage for the ever-increasing elephant population during drought years (Herremans 1995). Many other large trees are being claimed for dugout canoes in the Zambezi Valley, while virgin forests, most of them Mopane Woodland, are also being cleared to make way for crop cultivation, especially in Zimbabwe's Agricultural Regions 1-3, mainly in Mashonaland, where tobacco is heavily cultivated. ...
... The effects African elephants have on vegetation have been studied extensively (Osborn & Parker, 2003;Shannon et al., 2006;Boundja & Midgley, 2009;Chira & Kinyamario, 2009;Guldemond & Van Aarde, 2007;Ihwagi et al., 2010). However, research is limited on whether elephants are degrading or enriching habitats for invertebrate (Haddad et al., 2009) or vertebrate (Herremans, 1995;Cumming & Brock, 1997;Pringle, 2008) species. ...
In Africa, no other nonhuman animal fulfils the role of ecosystem engineers to the extent of the elephant. However, little is known about the relationship between elephant modified habitats and species composition of other animals. Our objective was to sample the herpetofauna within an Acacia habitat that varied in the degree of elephant impact. If elephant foraging was only modifying but not degrading or enriching the habitat, then herpetofauna species abundance and richness were predicted to be similar in elephant damaged and elephant excluded areas. We conducted this study at Endarakwai Ranch in northeastern Tanzania for 6 months in 2007 and 2008. We sampled herpetofaunal species richness and abundance within high, medium and low elephant damaged areas and in a plot that excluded elephants. Areas of heavy damage yielded higher species richness than the exclusion plot. Species diversity did not differ between the damaged areas and the exclusion plot. Frogs were more abundant in areas of high damage; in contrast, toads were found the least in high damage areas. The results support the notion that free ranging elephants influence herpetofaunal species distribution by creating habitat complexity through modifying the woodland area.
... Their activity can dramatically affect vegetation composition and structure, in particular of woody species [7][8][9][10]. Consequently, it also modifies animal biodiversity [11,12], as well as nutrient cycling and ecosystem productivity [13]. Moreover, elephants are responsible for crop-raiding, especially where cultivated land borders protected areas [14][15][16]. ...
This study investigates the ranging behavior of elephants in relation to precipitation-driven dynamics of vegetation. Movement data were acquired for five bachelors and five female family herds during three years in the Marsabit protected area in Kenya and changes in vegetation were mapped using MODIS normalized difference vegetation index time series (NDVI). In the study area, elevations of 650 to 1100 m.a.s.l experience two growth periods per year, while above 1100 m.a.s.l. growth periods last a year or longer.
We find that elephants respond quickly to changes in forage and water availability, making migrations in response to both large and small rainfall events. The elevational migration of individual elephants closely matched the patterns of greening and senescing of vegetation in their home range. Elephants occupied lower elevations when vegetation activity was high, whereas they retreated to the evergreen forest at higher elevations while vegetation senesced. Elephant home ranges decreased in size, and overlapped less with increasing elevation.
A recent hypothesis that ungulate migrations in savannas result from countervailing seasonally driven rainfall and fertility gradients is demonstrated, and extended to shorter-distance migrations. In other words, the trade-off between the poor forage quality and accessibility in the forest with its year-round water sources on the one hand and the higher quality forage in the low-elevation scrubland with its seasonal availability of water on the other hand, drives the relatively short migrations (the two main corridors are 20 and 90 km) of the elephants. In addition, increased intra-specific competition appears to influence the animals' habitat use during the dry season indicating that the human encroachment on the forest is affecting the elephant population.
... In the Zambezi Valley, Zimbabwe, Cumming et al. (1997) documented lower species richness of birds, ants and "total animals" (ants, bats, birds and mantises) in elephant-impacted sites than in non-impacted sites. Herremans (1995) recorded substantial changes in bird species composition in northern Botswana due to habitat modification by elephants, but noted that bird species ric hness may be increased if elephant impacts remained patchy. Rare antelope species such as bushbuck (Tragelaphus scriptus) are also adversely affected by the reduction in cover and quality browse (Addy 1993). ...
... However, these reserves are small (<1000 km 2 ) and surrounded by electric fences, essentially acting as an enclosed system, preventing the immigration and emigration of large mammals. As a result, elephant populations within these enclosed reserves need to be actively managed (Slotow & van Dyk 2004) to ensure that reserves do not become overpopulated, that genes can be exchanged, that elephants can meet all of their social, behavioural and other needs (Garaï et al. 2004), and so that the perceived negative impact on the vegetation by elephant (Anderson & Walker 1974;Herremans 1995) can be minimized. ...
African elephant have been reintroduced into small, enclosed reserves in South Africa, many populations being established with orphans <10 years old. This has resulted in abnormal behaviour in some elephant populations, which was corrected in Pilanesberg National Park by introducing older bulls and culling certain problem elephants. In July 2003, three older bulls (29-41 years old) were introduced into Phinda Private Game Reserve, KwaZulu-Natal, South Africa, in order to normalize the bull age structure and in an attempt to reduce the abnormally long musth period of one particular resident bull. These introduced bulls were monitored intensively after release, as was the resident bull population, both before and after introduction of the older bulls. The introduced bulls all came into musth within eleven months post release. The older bulls do not appear to have had any influence on the musth periods of the oldest resident bull (36 years old at introduction). Detailed behavioural studies of the effects of management actions on elephant populations, within small, enclosed reserves provide information and resources for future management decisions. This study demonstrates that old bulls can be successfully introduced to very small areas provided that electrification of the entire perimeter is secure. Further, the introduction has no detectable medium-term (one year) effect on the behaviour of a relatively dense population of resident elephants, and the welfare of the elephants was not greatly affected.
... Vegetation along the riverfront has been heavily impacted by elephants (Mosugelo et al., 2002) and is now dominated by shrubs, especially Croton megalobotrys (Mü ll.Arg.), Capparis tomentosa (Lam.) and Combretum mossambicense (Engl.; Herremans, 1995). Approximately 1-2 km from the river, the vegetation changes to a shrubwoodland mixture dominated by Baikiaea plurijuga (Harms) including Burkea africana (Hook.), ...
Background/Question/Methods
The piosphere effect describes a gradient of vegetation degradation that increases with proximity to water due to herbivore effects. Understanding and monitoring these effects is an important part of management in semi-arid systems. The African elephant (Loxodonta africana) is a prime contributor to piosphere effects due to its water-dependency and large size. We assess how vegetation degradation by elephants varies with distance to water in Chobe National Park, home to one of the largest elephant populations in Africa. Elephant utilization of vegetation was evaluated in thirty-four vegetation plots spanning over 60 km heading inland from the Chobe River.
Results/Conclusions
Regression analysis suggests that patterns differ between local and landscape scales. Branch utilization by elephants follows piosphere predictions at local scales. At landscape scales, branch herbivory initially follows piosphere predictions but then increases beyond the highly utilized riverfront section. Debarking at landscape scales linearly decreases with distance from river, fitting piosphere predictions but extending far beyond distances previously recognized in the literature. At local scales, debarking initially declines with distance to water but then increases beyond about 3 km. These varying patterns between debarking and branch utilization are suggested to relate to seasonal shifts in elephant diet and distribution in the park. They emphasize the importance of monitoring vegetation beyond a “zone of sacrifice” near water and of considering multiple types of vegetation utilization, as these may show divergent trends.
... Little is known of ecological processes in riverine woodlands, despite their importance as dry season concentration areas for mammals. Herremans (1995) suggests that Acacia woodlands growing along the rivers in N Botswana may have germinated during the 19th Century under a more humid climate, with low densities of wildlife and livestock as a result of the rinderpest outbreak and low numbers of elephant as a result of hunting. Riverine woodland might be incapable of regeneration under the current soil moisture regime when combined with high levels of herbivory. ...
... Indeed species richness of "other birds" was slightly higher in habitat modified by elephants. An alternative interpretation of the results would be that plant communities, rather than being "destroyed", are simply modified in ways that provide habitat for a different range of species, as was concluded by Herremans (1995) in his study of bird species diversity in elephant habitat of northern Botswana. Cumming et al. (1997) conceded the lack of reliable data on biodiversity impacts and called for further research to support the conventional wisdom that elephants at high densities (or even the somewhat arbitrary, and arguably low, density of 0.5 to 1 per km2) are "bad" for trees, elephants and other wildlife. ...
... Their activity can dramatically affect vegetation composition and structure, in particular of woody species (Holdo, 2003;Nelleman et al., 2002;Skarpe et al., 2004). Consequently, it also modifies animal biodiversity (Ben-Shahar & Macdonald, 2002;Herremans, 1995), as well as nutrient cycling and ecosystem productivity . Elephant are disproportionally responsible for crop-raiding, especially where cultivated land borders protected areas (Hoare, 1999;Jackson et al., 2008). ...
... Elephants are known ecosystem engineers, capable of altering landscapes by reducing plant biomass, changing species composition and increasing landscape patchiness (White & Goodman, 2009). The ability of elephants to transform landscapes is of major concern in elephantdominated areas (Herremans, 1995;Boundja & Midgley, 2010;Kalwij et al., 2010), as the impact of elephants on the vegetation could have negative consequences for species that require a particular vegetation structure (Skarpe et al., 2004;Pringle, 2008;Valeix et al., 2008). Increased elephant densities are related to severe declines in large tree abundance (Shannon et al., 2008;Kalwij et al., 2010). ...
Negative influences on the establishment and persistence of large trees used by tree-nesting birds as nesting sites represent a potential threat to vultures and raptors. We monitored large trees and their surrounding vegetation and analysed whether trees with nesting sites are at risk due to elephant impact. Trees with nests did not differ in elephant impact from control trees without nests, and the survival rates of trees with nests and the actual nests within the trees showed that nests decreased at a faster rate than the trees themselves. Elephant damage did not affect the persistence of nests over the 5-year monitoring period. However, the presence of insects and fungus on large trees was negatively related to tree survival, thereby indicating that elephant impact could indirectly facilitate insect and fungus attack and shorten the lifespan of a tree.RésuméL'influence négative des oiseaux qui utilisent les arbres pour y faire leur nid sur le recrutement et la persistance de grands arbres fréquentés constitue une menace potentielle pour les vautours et autres rapaces. Nous avons suivi de grands arbres et la végétation qui les entoure et nous avons vérifié si les arbres avec sites de nidification couraient plus de risques à cause de l'impact des éléphants. Les arbres avec nids ne différaient pas des arbres contrôle sans nid pour ce qui est de l'impact des éléphants, et le taux de survie des arbres avec nids et des nids eux-mêmes dans ces arbres montrait que les nids diminuaient à un rythme plus rapide que les arbres. Les dommages causés par les éléphants n'ont pas affecté la persistance des nids pendant les cinq années de suivi, mais la présence d'insectes et de champignons sur les arbres était liée négativement à la survie des arbres, ce qui indique que l'impact des éléphants pourrait faciliter indirectement les attaques d'insectes et de champignons et raccourcir la durée de vie des arbres.
... This serves as a measure of the robustness of the meta-analysis. Birkett 2002;Botha et al. 2002;Buechner & Dawkins 1961;Chapman et al. 1997;Cumming et al. 1997;Eckhardt et al. 2000;Fenton et al. 1998;Goheen et al. 2004;Guy 1981;Herremans 1995;Jachmann & Croes 1991;Keesing 1998;Leuthold 1977;Lombard et al. 2001 Study site characteristics may also influence these outcomes. While most of the data for plants show that elephants decrease abundance, for sites 6, 7, 9 and 13, there is no consistent pattern (figure 6.1a). ...
: Large herbivores such as elephants (Loxodonta africana) apparently have a negative impact on woody vegetation at moderate to high population densities. The confounding effects that fire, drought, and management history have may complicate assignment of such impacts to herbivory. We reviewed 238 studies published over 45 years and conducted a meta-analysis based on 21 studies that provided sufficient information on response of woody vegetation to elephants. We considered size and duration of studies, elephant densities, rainfall, fences, and study outcomes in our analysis. We detected a disproportionate citation of 20 published studies in our database, 15 of which concluded that woody vegetation responded negatively to elephants. Our analysis showed that high elephant densities had a negative effect on woody vegetation but that rainfall and presence of fences influenced these effects. In arid savannas, woody vegetation always responded negatively to elephants. In transitional savannas, an increase in elephant densities did not influence woody vegetation response. In mesic savannas, negative responses of woody vegetation increased when elephants occurred at higher densities, whereas elephants confined by fences also had more negative effects on woody plants than elephants that were not confined. Our analysis suggested that rainfall and fences influenced elephant density related impact and that research results were often site-specific. Local environmental conditions and site-specific objectives should be considered when developing management actions to curb elephant impacts on woody vegetation.
Background
African elephants can convert woodland to shrubland or grassland. Moderate conversion observed at low elephant densities may improve conditions for other animals, while extensive transformation at high densities may reduce plant and animal diversity. The threshold density separating facilitation from habitat destruction varies spatially and is partly determined by food choice, which differs between adult bulls and members of breeding herds. When elephants consume herbaceous forage, woodland damage is low but this increases when woody plants are the primary food source. Consequently, an understanding of diet selection by elephants is important for forecasting the degree of vegetation conversion. One hypothesis is that elephants select forage that provides the highest rate of intake. The mass harvested per trunkload is a constraint to intake and therefore this study sought to determine if trunkload mass changes seasonally; varies across common forage types utilised by elephants; and differs between adult bulls and members of breeding herds.
Methods
Mechanistic models were used to estimate the mass harvested per trunkload of green grass, mixed green and dry grass, forbs, and leaves and bark from woody plants across a heterogenous, semi-arid savanna at a daily time step for one annual cycle. Separate models were constructed for adult bulls and members of breeding herds.
Results
Harvestable mass changed seasonally for herbaceous forage and for leaves from woody plants but was constant for canopy bark. The maximum average trunkload mass of green grass was >75 times heavier than the bite mass reported for other grazers while trunkloads of leaves from woody plants were only eight times heavier than the bite mass reported for other browsers. This is attributed to the advantage provided by the trunk, which increases harvestable mass beyond the constraint of mouth volume, particularly when feeding on grass. Herbaceous forage yielded heavier trunkloads than leaves and bark from woody plants during the wet season, but this was reversed in the dry season. Adult bulls harvested heavier trunkloads than members of breeding herds for all forage types except forbs; and adult bulls harvested disproportionately large trunkloads of grass and bark.
Conclusion
The strong correlation between the model outputs and well-established trends in the seasonal changes in elephants’ diet suggests that elephants are preferential foragers of the largest trunkload on offer. Consequently, they are grazers when suitable herbaceous forage is available, and browsers when it is scarce. Green grass provides adult bulls with disproportionately large trunkloads and, therefore, adult bulls are predicted to have a strong preference for green grass. Availability of suitable green grass during the dry season may therefore buffer woodlands from heavy impact by adult bulls. Consequently, where possible, protected areas with elephants should aim to include key grass resources.
Research on human-elephant interactions (HEI) seeks to better understand relationships between people and elephants with the goal of reducing unwanted interactions for the long-term survival of elephants in social-ecological systems. Many examinations of HEI often rely on a short temporal scale of several seasons to several years, often because of limited data availability across time. These examinations offer limited understanding of processes that influence HEI and mutual adaptations of people and elephants. In this synthesis, I present an ethnographic case study from the Okavango Delta, Botswana, where human and elephant populations have increased in the past 20 years. I use bricolage, a practice of using available materials at hand, to weave together diverse historical and current scholarship and primary data to understand dynamics of HEI and coadaptation across three different periods (pre-colonial, colonial, and post-independence). I show that people and elephants were coadapted in the pre-colonial period when people were highly mobile and hunted elephants with rudimentary technologies in ways that supported human development across southern Africa with minimal impact on elephants. European colonization brought sweeping changes, including through the introduction of guns and the development of the ivory trade that led to massive declines in elephant populations. Development policies that were magnified in the years following independence, including the establishment of land policies that settled communities, additionally disrupted the formally fluid nature of HEI. Simultaneously, wildlife conservation policies that coincided with dramatic increases in elephant populations shape how people perceive HEI and elephants as a predominant environmental force today. I argue that the incorporation of wider historical contexts, where necessary through the practice of bricolage, reveals coadaptation across time and offers understanding of possibilities of coexistence where people and elephants thrive alongside each other.
Colophospermum mopane (mopane) forms mono-dominant woodlands covering extensive areas of southern Africa. Mopane provides a staple foodstuff for elephants, who hedge woodland by reducing trees to small trees or shrubs, leaving emergent trees which are too large to be pollarded. Emergent trees are important for supporting faunal biodiversity, but they can be killed by ringbarking. This study first examined the influence of elephant density on woodland transformation and the height distribution of canopy volume, and, second, whether canopy volume is maintained, and tall emergent trees too large to be broken can persist, under chronic elephant utilisation. Three regimes of 0.23, 0.59 and 2.75 elephants km ⁻² differed in vegetation structure and the height structure of trees. Areas under the highest elephant density supported the lowest total canopy volume owing to less canopy for plants >3 m in height, shorter trees, loss of most trees 6–10 m in height, but trees >10 m in height (>45 cm stem diameter) persisted. Under eight years of chronic utilisation by elephants, transformed mopane woodland maintained its plant density and canopy volume. Plant density was greatest for the 0–1 m height class, whereas the 3.1–6 m height class provided the bulk of canopy volume, and the 1.1–3 m height layer contained the most canopy volume. Emergent trees (>10 m in height) suffered a loss of 1.4% per annum as a result of debarking. Canopy dieback of emergent trees increased conspicuously when more than 50% of a stem was debarked, and such trees could be toppled by windthrow before being ringbarked. Thus relict emergent trees will slowly be eliminated but will not be replaced whilst smaller trees are being maintained in a pollarded state. Woodland transformation has not markedly reduced canopy volume available to elephants, but the slow attrition of emergent trees may affect supported biota, especially cavity-dependent vertebrate species, making use of these trees.
Identifying proper surrogate species or groups is a challenging but critical step in the application of surrogate species approaches in biodiversity conservation because their effectiveness can vary according to biological communities. Recently, the brood parasitic common cuckoo, Cuculus canorus, has been suggested as a surrogate for describing biodiversity, primarily based on its strong parasitic relationship with other host species. However, the efficiency of cuckoo surrogates has been challenged because of the potential limitations of the methodological approaches. Furthermore, its generality rarely has been explicitly tested in other parasitic species with local biodiversity data collected through conventional schemes such as grid-based sampling. Using bird survey data obtained from a grid-based sampling scheme in South Korea, we evaluated the surrogate efficiency of five cuckoo species for bird diversity (species richness and phylogenetic diversity) and generated surrogate species groups. We found that among the five parasitic cuckoo species breeding in South Korea, the common cuckoo and the Indian cuckoo C. micropterus were effective surrogate species. Among these, only the common cuckoo belonged to the best surrogate species group together with its major host species; the Indian cuckoo showed less effective surrogate efficiency than the common cuckoo. In conclusion, our study shows that the common cuckoo, as a single species and a member of a species assemblage, is an effective indicator species for bird diversity in grid-based survey data. However, the result that not all parasitic cuckoo species performed a surrogate role effectively implies that multiple functions may be associated with the surrogate efficiency of brood parasitic cuckoos, along with the importance of host-parasite relationships.
African elephants (Loxodonta africana) negatively influence woody vegetation, causing structural changes to ecosystems. Field-based survey methods used to monitor elephant impact, while valuable, are costly and time-consuming to execute. By applying distance-sampling techniques such as remote sensing technology, inaccessible areas can be surveyed. This overview provides insight into methods used by scientists to determine the impact of elephants on woody vegetation in sub-Saharan Africa. Data were sourced from a variety of research databases. Findings indicate that 87% (n = 92) of the reviewed studies used field-based methods and 13% (n = 14) used remote sensing-based methods. We explore the national affiliations of the lead and the last authors of the reviewed studies and the scientific journals that published them. Field-based is the dominant method used in the majority of published studies on elephant impact. The majority of these studies were published in European and American journals, instead of African journals, which are less represented. However, the majority of the lead and last authors’ affiliations for both field-based and remote sensing based methods are affiliated with African institutions. We conclude that there is a need to improve the integration of remote sensing techniques into conservation and other ecological fields.
The management of assemblages of species across many taxa is a common concern in conservation. Consequently, the use of one or a few surrogate or indicator species to represent an entire assemblage has become an increasingly important tool in conservation science. However, conservation schemes based on the needs of one or two focal species often fail to account for individualistic responses of larger assemblages of species. Data from bird point counts along with vegetation characteristics from a coastal tropical dry forest in Kenya that is subject to elephant disturbance were used to explore the differential responses of bird species to environmental conditions in a forest reserve where wildlife management includes both endangered birds and mammals. Results revealed that even birds with similar foraging habits had idiosyncratic responses to both environmental traits and elephant disturbance. While overall species responded to important characteristics such as percent canopy cover and leaf litter depth, individualistic responses of different species trait diversity defied easy characterization of optimal forest management schemes. Taken together, our analyses highlight the difficulty in basing the development of management plans for entire assemblages of species on the response of a single or a few species. Implications for wildlife conservation in Arabuko-Sokoke Forest and similar forest reserves are discussed, emphasizing the need for a better understanding of individual species’ responses to forest conditions.
The hypothesis that African elephants may cause the local extirpation of selected woody species was evaluated in a medium-sized, semi-arid reserve following their reintroduction at low density. Mortality, state-change, and regeneration of 25 tree and 17 shrub species were studied between 1997 and 2010. Annual mortality of shrub species ranged from 0.2 to 8.0%, with six species experiencing 6–8%. Eight shrub species lost more than half their adult population (range 10–94%). Annual tree mortality ranged from 0.2 to 10.5%. The two dominant dryland tree species experienced <1% annual mortality, 18 species lost more than half their tree population, and one was eliminated. Elephants accounted for >63% and stress-related agents >20% of tree deaths. The manner in which elephants induced tree death depended on species. The proportion of individuals of a species killed by pollarding or uprooting ranged from 0 to 74%, and by debarking from 0 to 100%. Complete uprooting was a common cause of death for three shrub species. Regeneration ranged from zero for six tree and one shrub species to a seedling every 7 m² for Colophospermum mopane and 23 m² for Dichrostachys cinerea in riparian habitat. Three shrub and eight tree species were identified as vulnerable to local extirpation owing to a combination of high mortality and poor regeneration that is likely to result in a considerably simplified system. Reintroduction of elephants into medium-sized reserves without regulation of their numbers may not be a desirable action.
Elephants have been transforming the Chobe Riverfront vegetation from a woodland state to a shrubland state. Subsequently along with the transformation certain woody species have shown low regeneration. Elephants have earlier been reported not to be an important factor directly affecting woody species regeneration, suggesting that other factors, such as fire and browsing ungulates may be responsible for the observed low woody species regeneration. There has been no fire along the Chobe Riverfront for the past decades, pointing to browsing ungulates as most plausible factor suppressing of woody species regeneration. Although most ungulates along the Chobe Riverfront have been either decreasing or stabilizing, the impala population has been increasing. This thesis tested the prediction that impalas invade elephant-modified habitats and subsequently retard regeneration of certain woody species. Specifically, the thesis address the following questions: 1) how has the riparian woodland plant community been influenced by elephant impact, 2) how has the Chobe impala population responded to the recovering of elephant population and associated woodland changes, 3) how are patterns of resource use by Chobe impalas associated with patterns of elephant impacts on vegetation, and 4) can impala herbivory restrict woodland regeneration in the Chobe riparian woodland.
Generally, densities, species diversities, functional diversity and functional dominance of woody species were higher on sites that were lightly disturbed than sites that were heavily disturbed by elephants. On each site dominant species had functionally minors species. Effect of elephant disturbance on dominant species was influenced by soil type. On Kalahari sandy soils, 75% of species dominating on lightly disturbed sites decreased in abundance on heavily disturbed sites. Of these decreasing dominant species, only 33% had functionally similar species that were mionor on lightly disturbed sites increasing in abundance on heavily disturbed sites. On alluvial soils, 20% of species dominating on lightly disturbed sites decreased in abundance on heavily disturbed sites, and had functionally similar species which were mionor on lightly disturbed sites increasing in abundance on heavily disturbed sites. Along the Chobe Riverfront the impala population increased with increasing openness of the woodland, and used elephant-modified habitat more than relatively unmodified habitats. Within 2 km of Chobe River the capita growth rate of elephants increased at an increasing rate until 1980s when it started to increase at a decreasing rate. Meanwhile, the capita growth of impala increased at a slow rate until 1980s when it started to increase rapidly. During the
ii
dry season impalas browsed more than expected on the shrubland and riparian woodland, did not show any browsing preference or avoidance for mixed woodland and browsed less than expected in Baikiaea woodland. An exclosure experiment showed that the presence of ungulates significantly decreased the likelihood of tree seedling survival. Ungulate browsing was also the most common damage type to surviving tree seedling in this experiment. Proportions of tree seedlings surviving were negatively correlated with impala biomass, but were not significantly correlated with kudu and elephant biomasses along the Chobe Riverfront.
The results presented in this thesis support the prediction that impalas invade elephant-modified habitats and through selective browsing retard and alter the composition of woody species regeneration. Impalas’ preferences of elephant-modified habitats, where they browsed more than expected might have contributed to the low density and diversity of woody species below 1 m along the Chobe Riverfront. The interaction between elephant browsing, that open the woodland, and impala browsing, that lower woody species regeneration, might have created irreversible states within the woody species community, such that elimination of either elephants or impalas may not revert the woodland state along the Chobe Riverfront. Thus, the Chobe Riverfront appears to be locked into one-way directional shift from a woodland state towards a shrubland state.
When elephant densities exceed approximately 0.5 per km2, savanna woodlands are generally converted to shrublands or grasslands. The impact of such elephant-mediated habitat change on biodiversity in African game reserves has seldom been measured. We examined species richness of woody plants, birds, bats, mantises and ants in reserves where elephants had destroyed the miombo woodland and in adjacent but intact miombo woodlands outside the reserves. Species richness of woodland birds and ants was significantly lower where elephants had removed the tree canopy. Our findings may have important policy implications for conserving biodiversity in many African reserves in the face of rapidly growing elephant populations (approximately 5% per annum). The problem is further compounded by international public pressures against reducing elephant densities within game reserves while, outside these protected areas, savanna woodlands and their associated faunas are being lost to agriculture. Where then will refugia for habitat-sensitive species exist if not within the region's largest protected areas?.
The potential long-term influences of mesobrowsers versus those of savannah elephants on woodland dynamics have not been explored. This may be a critical omission especially in southern African savannahs, where efforts to preserve existing woodlands are typically directed at elephant man-agement. We describe a simple browse–browser model, parameterized from an extensive review of the literature and our own data, including quantitative assessment of impala impact, from the study site, iMfolozi Park, South Africa. As there is a paucity of species-specific demographic data on savannah woody species, we modelled, in a novel approach, functional groups of plant species typical of Acacia wood-lands. Outputs suggest that over the long term (100 years), low-to-moderate densities of impala will have a similar impact on woodland structure, in terms of density of adult trees, as low-to-moderate densities of elephant. Further, the outputs highlight the apparently strong synergistic effect impala and elephant impacts combined have on woodland dynamics, suggesting that reduction or removal of either impala or elephant will radically reduce long-term destruc-tion of savannah woodlands. Recorded changes in adult tree numbers in iMfolozi broadly supported the model's outputs. R esum e Les influences potentielles a long terme des m eso-herbivores sur la dynamique des for^ ets n'ont pas encore et e explor ees par rapport a celles des el ephants de savane. Ceci pourrait ^ etre une omission importante en ce qui concerne les savanes d'Afrique australe o u les efforts pour pr eserver les for^ ets existantes sont g en eralement orient es vers la gestion des el ephants. Nous d ecrivons un mod ele simple consommation-consommateur, param etr e a partir d'un examen approfondi de la litt erature et de nos propres donn ees, y compris une evaluation quantitative de l'impact des impalas sur le site etudi e, le Parc d'iMfolozi, en Afrique du Sud. Comme il existe tr es peu de donn ees d emographiques sp ecifiques, par esp ece, sur les esp eces ligneuses de savane, nous avons mod elis e, dans une approche nouvelle, des groupes fonctionnels d'esp eces v eg etales typiques des for^ ets d'Acacia. Nos r esultats sugg erent qu' a long terme (100 ans), des densit es faibles a mod er ees d'impalas auront sur la structure foresti ere un impact comparable, en termes de densit e d'arbres adultes, a celle de densit es faibles a mod er ees d' el ephants. De plus, les r esultats soulignent l'effet synergique apparemment puissant qu'ont les impacts combin es des impalas et des el ephants sur la dynamique des for^ ets, laissant penser que la r eduction ou l'enl evement des impalas ou des el ephants pourront radicalement r eduire les destructions a long terme des for^ ets de savane. Les changements enregistr es dans le nombre d'arbres adultes a iMfolozi soutiennent largement les r esultats du mod ele.
(1) Multiple stable states in ecosystems have been proposed on theoretical grounds, and examples have been offered, but direct tests of the predictions are lacking. A boundary between states exists if: (i) a system when disturbed from one state to another does not return to its original state once the cause of the disturbance returns to its original value; and (ii) a second factor takes over and holds the system in the new state. We examine these predictions for two stable states in the woodlands of the Serengeti-Mara ecosystem in East Africa. (2) Woodlands in natural areas of savannah Africa have declined over the past 30 years. Three general hypotheses have been proposed: (i) expanding human populations have concentrated elephants into protected areas, elephants then caused the decline of woodlands but man-induced fires prevented regeneration (two stable states); (ii) fires caused the decline and also prevented recovery (one stable state); (iii) fires caused the decline while elephants inhibited recovery through density-dependent mortality of seedlings (two stable states). (3) Two time periods, the 1960s when woodlands changed fastest and the 1980s when grasslands prevailed, produced four specific hypotheses. (i) `The 1960s elephant hypothesis' and (ii) `the 1960s fire hypothesis' hold that elephants and fire, respectively, caused woodland change. (iii) The `1980s elephant hypothesis' and `the 1980s fire hypothesis' hold that these factors, respectively, prevented woodland recovery. (4) From experiment and observation of seedling recruitment, mortality due to combinations of burning rates, elephant browsing, wildebeest trampling, and antelope browsing was estimated and used to model tree population dynamics; predictions for rates of decline and increase were compared with independent estimates from aerial photographs. (5) Maximum rates of elephant and antelope browsing could not have caused the observed decline of woodlands in the 1960s. The most conservative burning rates in the 1960s, without elephants, could have caused a decline consistent with the 1960s fire hypothesis. (6) The combined impact of fire and browsing most closely matched the observed rate of woodland loss. (7) Wildebeest grazing in the 1980s reduced dry grass and minimized fire incidence. The model predicted that fire mortality and wildebeest grazing could not maintain the present grassland state. (8) The present high elephant density was sufficient to prevent an increase in the woodlands consistent with the 1980s elephant hypothesis. Wildebeest trampling and other browsers ensures that the vegetation is currently stable in a grassland state. (9) Thus, an external perturbation, such as fire, was necessary to change the vegetation from woodland to grassland. Elephants were unable to cause such a change. Once the grassland was formed, however, elephants were able to hold it in that state. These results are consistent with the third general hypothesis that there are two stable states of woodland and grassland, the latter maintained by herbivores. (10) Simulation of conditions in the 1890s suggests that the rinderpest epidemic combined with elephant hunting could have caused the woodland regeneration observed before the 1950s. Therefore, (i) savannah woodlands may regenerate in pulses as evenaged stands, and (ii) there may have been more grassland in Africa before 1890. This longer time-scale view of the dynamics of vegetation has implications for the conservation of elephants and their habitats.
Diversity indices are frequently applied in the form of ratios of absolute diversity to the maximum diversity possible. Regardless of whether the maximum diversity is defined to be limited by the number of species or by the number of individuals present, the resultant indices can be shown to possess mathematically undesirable qualities. All such indices, including equitability as measured by Pilou's J and J', Lloyd and Ghelardi's ratios, redundancy, and the scaled diversity formulations of Fager, are inappropriate for most ecological applications.
The influence of the African Elephant on the vegetation of the Kruger National Park
A survey of elephant impact at various distances from roads was conducted in June 1978 for Sclerocarya caffra (marula) tree populations in Acacia nigrescens Tropical Plains Thornveld in the Kruger National Park, Republic of South Africa. Data from scar recovery indicate that widespread scarring of S. caffra trees by elephant commenced in 1973, coinciding with a wet cli- matic phase. Elephant impact, old and fresh and irrespective of kind, decreased with distance from roads. Substantially higher impact was also recorded along S. caffra population boundaries. The most recent impact on some populations was higher than expected from the established relationship between elephant impact and tree density.
Olifantinvloed op groot Acacia nigrescens (knop- piesdoring) borne in die Punda Milia-Sandveld van die Nasionale Krugerwildtuin, is in Desernber 1978 ondersoek. 'n Monster van 951 borne toon dat die voortbestaan van die boornpopulasie bedreig word. Elephant impact on Acacia nigrescens trees in a section of the Punda Milia-Sandveld of the Kruger National Park. An investigation of elephant impact on tall Acacia nigrescens trees in the Punda Milia- Sandveld of the Kruger National Park was conducted during December 1978. A sample of 951 trees showed that the tree population is endangered.
Aspects of reproduction in the African elephant in the Luangwa Valley in Zambia were studied in relation to the population dynamics of the species. The fetal and the secondary sex ratio up to 16 years of age did not depart significantly from equality. Males left family units soon after 16 years of age and joined bachelor herds. From 1964 to 1968, 88% of conceptions were in the rains, but in 1969 there was a shift in the breeding season peak to the dry months of the year. There was no evidence of seasonal breeding in the male elephant. Females reached maturity at 14 years, and males at 15 years, when the combined weights of the testes reached 650 to 700 g, and the mean seminiferous tubule diameter reached 90 to 120 μm. The mean calving interval was 3·5 to 4·0 years. In the population, 6% of the elephant were less than 1 year old. Apparent cycles of recruitment were considered to be artefacts caused by slight inaccuracies of the ageing technique used. Corpora albicantia accumulated at the approximate mean rate of 0·6/year, and the significance of this was examined in relation to comparative studies of population fertility. Reproductive senescence was a consequence of a combination of uterine defects and a reduction of oocyte number.
Palaearctic migrant passerines and near‐passerines which visit eastern Africa can be divided into six groups based on the latitude of their final wintering area. Species wintering further north in Africa tend (a) to breed in more southern parts of the Palaearctic, (b) to prefer drier habitats and (c) to feed more from the ground than those wintering further south. Many species use quite narrow passage routes through eastern Africa and, for some species, passage is centred further east in spring than in autumn. Southward migration can take more than 4 months from the Palaearctic breeding grounds and many birds stopover in the northern tropics from September to November. By contrast, the return migration takes only about 6 weeks. The timing and strategy of migration within Africa can be broadly related to seasonal patterns of rainfall and vegetation.
Rarefaction is a method for comparing community diversities that has consistently been abused by paleoecologists: here its assumptions are clarified and advice given on its application. Rarefaction should be restricted to comparison of collections from communities that are taxonomically similar and from similar habitats: the collections should have been obtained by using standardised procedures. The rarefaction curve is a graph of the estimated species richness of sub-samples drawn from a collection, plotted against the size of sub-sample: it is a deterministic transform of the collection's species-abundance distribution. Although rarefaction curves can be compared statistically, it may be more efficient to compare the species-abundance distributions directly. Both types of comparison are discussed in detail.
The objectives of this chapter are to discuss which habitats migrants choose for the winter quarters, and how they use these habitats. This discussion will focus on small migrant land birds that move from high to tropical latitudes. Therefore, the term “migrants” refers to north temperate species that winter at tropical and subtropical latitudes, and the term “residents” will refer to local, tropical, resident species.
So far this book has concentrated on the measurement of species diversity. Yet there are many studies concerned with other varieties of diversity. Attempts by ecologists to explain why some areas are species rich and others are species poor or why a species is abundant in one location but rare in another often prompts an investigation of habitat diversity. In undertaking a study of habitat diversity ecologists are asking similar questions to the ones they pose when describing species diversity. The methods devised for measuring species diversity are also employed when niche width is being investigated. Niche width is, after all, a measure of the diversity of resources utilized. The first section of this chapter therefore looks at other contexts in which measures of species diversity can be utilized.
Two woodland populations were surveyed in Ruaha National Park to assess the effects of browsing by Loxodonta africana. Some 40% of the Acacia albida trees were dead, and 67% of the Commiphora ugogensis trees had been killed during the previous 6 yr. The size distribution of both species showed a lack of regeneration and both populations are therefore in decline. The proportion of A. albida trees killed by elephants increased with tree density, but the proportion of C. ugogensis trees killed was independent of tree density. Evidence from the literature suggested two more mortality patterns caused by elephant browsing: 1) the proportion of trees killed decreased with tree density; 2) elephants killed a fixed number of trees rather than a proportion of the population. Simple deterministic models showed that very large numbers of elephants need to be killed in order to stabilize or reverse the woodland decline. The 4 browsing mortality patterns mean that different tree species behave differently under the same elephant population and therefore the benefit/cost ratio of culling (number of trees saved per elephant shot) is higher for some species than for others. The benefit/cost ratio declines rapidly with time: to be effective culling must start early.-Author
The preferred habitats of the African bush elephant, Loxodonta africana, are forestedge, woodland, bushland and wooded or bushed grassland. Increasing amounts of grass in the elephants' diet are correlated with conversion of wood habitats towards grassland, and with increasing elephant mobility, poorer physical condition, and progressively increasing natural regulatory processes leading to decrease in numbers. Elephant occur in discrete unit populations. Each population shows a series of highly contagious instantaneous distributions which, when averaged over a period of time, probably tend, in a uniform habitat, to approach a random or regular distribution. High densities or disturbance by man lead to increase in mean group size and more uneven distribution. The effect on woody vegetation is greater and more lasting than on grass or herbs and usually radiates outwards from the initial centre of damage. The typical cycle begins with destruction of the understory, followed by ringbarking of adult trees, and is accelerated by fire. Several case studies involving forest, moist and dry woodlands, and dry bushland are described which fit this pattern. /// Предпочитаемые местообитания Африканских слонов Loxodonta africana - опушки леса, лесистые местности, кустарник и открытые участки с деревьями или кустами. Увеличение относительного количества травы в диете слонов коррелирует со сменой лесных местообитаний открытыми, увеличением подвижности слонов, ухудшением физических условий и усилением действия естественных регулирующих процессов, ведущих к снижению поголовья. Слоны встречаются отдельными разрозненными популяциями. Каждая популяция образует ряд временных, вступающих в контакт группировок, которые при анализе в среднем за определенный промежуток времени очевидно имеют тенденцию к однородным местообитаниям, и их распределение приближается к рандомическому распределению. Высокая плотность и влияние деятельности человека приводит к увеличению стад слонов и еще более неравномерному распределению. Повреждения древесной растительности более сильные и длительные, чем травянистой. Обычно эти повреждения распространяются вширь от одного исходного очага. Типичный цикл смены местообитаний начинается с уничтожения подстилки и обгрызания коры на деревьях. Эта деятельность усугубляется пожарами. Приведены некоторые случаи исследований во влажных и сухих лесах и сухих кустарниках, которые подтверждают эту схему.
An explicit means of calculating the expected number of species [E(S"n)] and the variance of (S"n) in a random sample of n individuals from a collection containing N individuals and S species is presented. An example illustrates a new use of E(S"n): determination of the sample size required for any desired degree of accuracy in collecting species known to occur in a particular area.
(1) The seasonal pattern of occurrence of the Palaearctic-breeding landbird migrants in Tsavo East National Park in south-eastern Kenya is described. (2) The majority of the migrants did not arrive in the autumn until the onset of the rains, usually about mid-November. By this time they had been in Africa south of the Sahara for 2 or 3 months. (3) Those species feeding on the ground and in the air remained in Tsavo East N.P. for the remainder of the northern winter. (4) Those species feeding in the woody vegetation moved on by mid-January, presumably farther south, and then returned in smaller numbers during April. (5) The arrival in November appeared to be largely the result of typical long-distance nocturnal migration. (6) The patterns of occurrence can be explained in terms of the available food supplies, and there is circumstantial evidence for the suggested movements from ringing studies carried out at a nearby site. (7) It is suggested that the migrants have adopted the strategy of always living in areas with an abundance of resources and moving on when these become reduced; and that the only real difference between the so-called Palaearctic migrants and those that migrate within Africa is that of distance moved.
Humans and elephants are complete competitors. Biological theory maintains that such species cannot co‐exist on the same range and that increase in one will exclude the other. Measurements of human increase, elephant decline and ivory production are in keeping with this hypothesis.
1. The effect of disturbance on a biological community is commonly measured by a change in an index of community structure. When such an index is calculated from a sample from the community, it is important to assess the statistical significance of an observed change. 2. A simple randomization test is described for testing for change in community structure. The test can be used in conjunction with any measure of community structure based on observed species abundances such as diversity indices. An example is given.
General patterns of density, species richness, and relative abundance of breeding birds are examined in a wide variety of North American forests. Taking data from censuses published in American Birds, we use rarefaction to ordinate the species richness of communities in terms of samples of equal numbers of individuals. By this criterion young forests in secondary succession and mature deciduous forests can be equally rich in bird species; coniferous forests and dense successional stands having only one or two species of trees have the fewest species of birds. For our data set the density of birds is higher in mature deciduous forests than in successional stands. The species/area relationship (s/a) is a function of both this species/individuals relationship (s/n) and the individuals/area relationship (n/a). According to the Jonckheere-Terpstra statistic there is a statistically significant pattern to the order in which bird communities fall with regard to s/n and n/a. To see these relationships in terms of the structure of the vegetation, we present the positions of 56 stands in a graphic space determined by principal components. Tree species richness and canopy cover dominate the first axis, and variation in canopy height the second. Tree density has a somewhat independent pattern of variation and is expressed by the third axis. In the bivariate space of principal components one and three, a SYMAP contour diagram of the number of bird species expected in 10 ha (s/a) shows maximal values in mature deciduous forests, but not in those that have the highest trees species richness, canopy height, or tree density. The number of individual birds/10 ha (n/a) shows a similar pattern except that maximal density occurs at maximal values of tree species richness and canopy height. By this criterion both bird species richness and density are minimal in coniferous forests characterized by high tree density, low canopy, and few species of trees. These patterns are not discernible by the classic bird species diversity/foliage height diversity method proposed by Mac Arthur and Mac Arthur in 1961. They are masked by correlation coefficients, partly because the coefficients are insensitive to nonlinear relationships. We recommend rarefaction, principal components analysis, and contour diagrams to display relationships among communities.
Seven major habitats were designated, ranging from open grassland to woodland with a small area of riverine forest. Seeds and arthropods showed main peaks of abundance in December and January and a smaller peak after the 2nd wet season. In the 5 more open habitats fruits also peaked in abundance in the latter part of the wet season, but in the woodland the fruits of Commiphora spp. were most available from June to September. Nectar was important only to sunbirds, which were not a significant part of the bird community in any habitat. The number of granivores and insectivores greatly increased in the wet seasons, because of immigration. Granivorous visitors were all African migrants, but 2/3 of insectivorous species were Palearctic migrants. In woodland there was a 2nd but smaller peak of numbers of birds coinciding with fruiting of Commiphora in the dry season, predominantly resident species eating both fruit and insects. In open habitats density, biomass and energy requirements were lowest in the dry season and increased 5-fold in the wet seasons. Average density, biomass, energy requirements, and number of species were broadly correlated with increasing complexity of vegetation. -from Author
Three small elephant populations have survived in South Africa despite near extermination in the recent past. In Tongaland a group of fewer than 30 bulls survives by keeping contact with the population in a nearby reserve; in the Knysna, where there were 13 in 1920, there are now 12; and in the Addo Bush 11 survivors in 1931 had increased to only 18 in 1953, but to 102 in 1979. The author tells the story of each group, discusses the reasons for the different status of each, and describes what is being done to conserve them.
Dr Laws was the first Director of the Tsavo Research Project. This was started in February 1967 to investigate the habitat destruction in the Tsavo National Park, in Kenya, and the part played by the elephants which had been increasing rapidly—the research team's estimate was 23,000 in the park with an additional 12,000 in the peripheral areas, a total of 35,000 ± 7,000. After nine months the research programme, which included sample kills of elephants, was interrupted by the National Parks. Dr Laws spent the next eight months trying to restart the work and to discuss his findings and proposals; no discussions took place and he resigned. The article here consists of part of a paper (slightly amended by Dr Laws) published in the Journal of Reproduction and Fertility, Supplement No 6, 1969, and reproduced by permission. It explains why he regards the sample cropping as essential to find out what is happening in the elephant populations, and whether they are regulating their numbers quickly enough to save the habitat. Since Dr Laws left the Tsavo in June 1968, the Research Project has been carried on under the direction of the Botanist Warden, Dr P. E. Glover, an article by whom appeared in the September ORYX, page 323; a comment on this by Dr Laws will appear in the next ORYX, May 1971.
Data on passerine migrants in West Africa published since the works of Moreau j 1972) and Curry-Lindhal (1981) are reviewed and new information on wintering ranges are summarized. An important feature of West Africa as a wintering zone is the presence of the two great river basins of the Senegal and the Niger, which are responsible for the Sahel being far richer than would be expected at this latitude. This ‘paradoxical’ or ‘green’ Sahel is under the threat of agricultural developments and of increasing desertification. Conversely, Palaearctic migrants can take advantage of the new-savanna/forest mosaics and agricultural developments which have replaced the rain forest.
The reduction in canopy cover of the Seronera woodlands since the mid‐ 1960s can be largely attributed to the destruction of mature Acacia tortilis trees by elephants. The development of the tree regeneration that has colonized the gaps in the mature canopy is being suppressed by giraffe browsing and periodic burning. A simple model is presented which simulates these impacts upon the dynamics of the A. tortilis population. Height‐specific impact rates of these three agents are quantified. Between 1968 and 1977, mature trees were lost at a mean annual rate of some 6%, although this figure showed considerable annual variation (13.5‐2%). Combinations of impact rates, simulating possible natural developments within the Serengeti woodlands, are programmed into the model to assess their effects upon the tree population structure. The results suggest that measures to promote regeneration development (fire protection and/or giraffe culling) are more effective in the long‐term to encourage mature canopy recovery than are measures to reduce mature tree mortality (elephant culling). The management implications of these results are considered, and their extrapolation to other wildlife conservation areas experiencing similar declines in mature canopy woodland is discussed. It is suggested that the effects of the combination of low elephant densities and high giraffe densities prevalent in the Serengeti produce a dynamic system in which the woodland structure oscillates between mature canopy and open regeneration‐grassland phases. The woodland structure desired by Park management to ensure continuity of mature tree canopy represents an unstable transitional stage between these two phases.
Résumé
La réduction du couvert végétal dans les forêts de Seronera depuis les années 1965–1970 peut être largement attribuée ai la destruction des Acacia tortilis par les éléphants. Le développement de la régénération des arbres ayant colonisé les espaces libres du couvert végétal est anihilé par le broutage des girafes et les incendies saisonniers. On présente un modeile simple qui simule ces impacts sur la dynamique de population de Acacia tortilis . Pour ces trois facteurs, les taux d'impact spécifique de la hauteur sont quantifiés. Entre 1968 et 1977, le taux de perte
Elephant damage to woody plant species in northern Botswana was distinguished from damage caused by fire, and other unknown factors. Elephant-induced damage to trees and shrubs that dominated the vegetation biomass in 33 sites suggested that elephants had a more or less random impact on the vegetation throughout their distribution range although the total biomass removal was low. Three principal patterns of vegetation utilization became apparent: (1) there was a hight variation in the proportion of woody plants damaged by elephants, particularly in the vicinity of permanent water sources; (2) the proportion of important food plants damaged by elephants increased significantly with the proximity of plants to temporary water sources; (3) there was a clear distinction between the effects of elephants and fire on different plants species. Ordination analyses suggested that the vegetation in northern Botswana could be classified into three zones containing (1) high fire impact and low elephant damage; (2) high elephant impact and low fire damage; and (3) minor damage by elephants and/or fire.
The trend in the volume of African ivory coming onto the world market suggests that African elephant populations have declined progressively since at least 1950 and that the rate of decline is presently accelerating. The process is well-advanced in East Africa where few elephants are predicted to survive beyond 1995 outside high-security areas. A similar trend is deduced for Africa as a whole but lagged about 20 years behind that of East Africa.
The problem of ‘excess Elephants’ in Tsavo National Park, Kenya, came to a head with the die-off during the 1970–1971 drought. Like many parts of Africa, Tsavo is being threatened in its workings—and, in the long run, in its existence—by the pressure of people in the environs. Tsavo's present travails epitomize many of the threats facing Africa's wildlife refuges. These problems of conservation require solutions that are much more complex than they would have been in the past—solutions which will reflect the balances of the entire environment, outside the park as well as inside. A wildlife ecosystem demonstrates characteristics which can scarcely be predicted from the properties of its constituent components. It embodies a different and higher level of organization (an ‘emergent quality’) which cannot be perceived by looking with microscopic intensity at any particular part, but only with a microscopic perspective at the total pattern. By extension, Tsavo can be taken as a measure of how far people around the world are ready to assist in safeguarding Africa's wildlife, and what costs they are willing to bear—in terms of their pockets and philosophies alike. This survey of the present position at Tsavo attempts to propose perspectives which do not always receive as much attention as they should.
This paper presents data on elephant distribution and abundance in northern Botswana and uses these as a basis for considering conservation problems with this species.Although the land available to elephants will inevitably be reduced in years to come, the Wildlife Management Area system is seen as the key to the long-term survival of elephants in large numbers in northern Botswana.The main problem in assessing management options to deal with the elephant overabundance problem in the Chobe National Park is suggested to be the absence of a management plan giving conservation and management goals for the area.
The recent literature on species diversity contains many semantic, conceptual, and technical problems. It is suggested that, as a result of these problems, species diversity has become a meaningless concept, that the term be abandoned, and that ecologists take a more critical approach to species-number relations and rely less on information theoretic and other analogies. As multispecific collections of organisms possess numerous statistical properties which conform to the conventional criteria for diversity indices, such collections are not intrinsically arrangeable in linear order along some diversity scale. Several such properties or "species composition parameters" having straightforward biological interpretations are presented as alternatives to the diversity approach. The two most basic of these are simply =the proportion of potential interindividual encounters which is interspecific (as opposed to intraspecific), assuming every individual in the collection can encounter all other individuals, and =the expected number of species in a sample of n individuals selected at random from a collection containing N individuals, S species, and Ni individuals in the ith species.
Evidence for an increasing elephant population m northern Botswana - Department of Wildlife and National Parks
- G W Calef
Bird Research Priorities for Botswana Conservation status and prospects for birds in Botswana -Department of Wildlife and National Parks
- M Herremans
Research priorities and projects of the ornithology research unit Dept of Wildl and National Parks
- M Herremans
Long-term data series relating to southern Africa's renewable natural resources South African National Scientific Programmes
- A J Viljoen