Article

Do Changes in Elephant Abundance Affect Forest Composition or Regeneration?

Authors:
  • Nature Conservancy of Canada
If you want to read the PDF, try requesting it from the authors.

Abstract

While overall numbers of African elephant have declined dramatically in recent times, some populations are now confined to protected areas and are locally overabundant-an undesirable situation for both biodiversity conservation and elephants. In forested protected areas, options to manage elephants are limited because it is difficult to safely approach animals, yet it is vital that these populations are managed because browsing by elephants can dramatically alter forest ecosystems. Using data collected over 50 yr in Kibale National Park, Uganda, we examine the prediction that increasing elephant numbers and associated changes in their foraging behavior have caused a shift in tree community composition. Although the relative abundance of elephants increased significantly between 1996 and 2010, the population structure of their preferred tree food species did not change, nor did tree community composition change in favor of species able to re-sprout after elephant damage. Furthermore, over the last 50 yr Kibale elephants have not become more selective foragers, as would be expected if more nutritious tree species were declining. However, elephants are more abundant in disturbed areas dominated by shrubs and grasses and appear to have arrested forest succession in these areas. At their current abundance, elephants have not selectively altered the composition of intact old growth forest, but they do inhibit the regeneration of disturbed areas.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Plant functional diversity in ED2 is represented by three plant functional types (PFTs): early-successional trees (shade-intolerant, fast-growing pioneers, low wood density), mid-successional trees (intermediate) and late-successional trees (shade-tolerant, slow-growing, canopy-dominant and high wood density) (see the PFT parameters in Supplementary Table 1). We represented elephant disturbance by increasing the mortality of trees with diameters <30 cm based on observations of plant survival rates from browsing or trampling 18,19 . Mortality was inversely proportional to tree size and proportional to animal population density 4 . ...
... Elephants thus by-pass the natural succession initiated by tree fall that creates the gaps that allow the recruitment of light-demanding species with low wood density-a process that constrains AGB 28 . Short-term (10-30 yr) variations in forest properties when elephant densities change are subtle and mainly involve the demography of young trees (Table 1), as reported previously 19 . The effect of elephants becomes more evident in the medium term (50-150 yr; Fig. 1). ...
... Seed dispersal and nutrient transport may affect plant species composition, carbon stocks 10,30 and primary productivity at large scale and over very long periods 31 . Elephants may also further suppress tree recruitment and maintain light gaps through frequent visitations, although this mechanism has been observed more frequently in logged forests 19 . The large-scale effects over the entire African forest depend critically on the actual area under elephant disturbance, and on the spatial patterns of trails 17 ; we accounted for this in our estimate in a highly simplified manner (see Methods). ...
Article
Full-text available
Large herbivores, such as elephants, can have important effects on ecosystems and biogeochemical cycles. Yet, the influence of elephants on the structure, productivity and carbon stocks in Africa’s rainforests remain largely unknown. Here, we quantify those effects by incorporating elephant disturbance in the Ecosystem Demography model, and verify the modelled effects by comparing them with forest inventory data from two lowland primary forests in Africa. We find that the reduction of forest stem density due to the presence of elephants leads to changes in the competition for light, water and space among trees. These changes favour the emergence of fewer and larger trees with higher wood density. Such a shift in African’s rainforest structure and species composition increases the long-term equilibrium of aboveground biomass. The shift also reduces the forest net primary productivity, given the trade-off between productivity and wood density. At a typical density of 0.5 to 1 animals per km², elephant disturbances increase aboveground biomass by 26–60 t ha⁻¹. Conversely, the extinction of forest elephants would result in a 7% decrease in the aboveground biomass in central African rainforests. These modelled results are confirmed by field inventory data. We speculate that the presence of forest elephants may have shaped the structure of Africa’s rainforests, which probably plays an important role in differentiating them from Amazonian rainforests.
... Moreover, tree growth and recruitment may have been slowed by early competition from the rapid establishment of dense herbaceous and shrubby vegetation (Donato et al., 2012) and increased elephant activity. Elephants are known to forage extensively on these shrubs (Paul et al., 2004;Lawes and Chapman, 2006;Duclos et al., 2013;Omeja et al., 2014). Based on the measured structural attributes and continued dominance of herb and shrub vegetation, our study supports previous findings that logged forest in KNP is in an arrested state of succession Chapman, 1997, 2004;Bonnell et al., 2011). ...
... Such events have recently been reported for KNP, including changing climates (i.e. longer drought events since the mid-1990s (Hartter et al., 2012) and increased elephant abundance and activity (Omeja et al., 2014). ...
... We show in this study that a tropical forest may remain with the imprint of logging for many decades. Furthermore, persistent effects of selective logging have exerted cascading effects on other trophic levels, particularly affecting the population dynamics of primates (Chapman et al., 2010b;Bonnell et al., 2011) and movements of elephants (Omeja et al., 2014). Interestingly, logging extraction levels in KNP ranged from 14 to 17 m 3 /ha (Struhsaker, 1997), comparably less than the 32.5 m 3 /ha reported by Blanc et al. (2009) for a selectively logged forest in French Guiana that rapidly recovered AGB within 40 years. ...
Article
Full-text available
Selective logging of tropical forests is increasing in extent and intensity. The duration over which impacts of selective logging persist, however, remains an unresolved question, particularly for African forests. Here, we investigate the extent to which a past selective logging event continues to leave its imprint on different components of an East African forest 45 years later. We inventoried 2358 stems ≥ 10 cm in diameter in 26 plots (200 m × 10 m) within a 5.2 ha area in Kibale National Park, Uganda, in logged and unlogged forest. In these surveys, we characterized the forest light environment, taxonomic composition, functional trait composition using three traits (wood density, maximum height and maximum diameter) and forest structure based on three measures (stem density, total basal area and total above-ground biomass). In comparison to unlogged forests, selectively logged forest plots in Kibale National Park on average had higher light levels, different structure characterized by lower stem density, lower total basal area and lower above-ground biomass, and a distinct taxonomic composition driven primarily by changes in the relative abundance of species. Conversely, selectively logged forest plots were like unlogged plots in functional composition, having similar community-weighted mean values for wood density, maximum height and maximum diameter. This similarity in functional composition irrespective of logging history may be due to functional recovery of logged forest or background changes in functional attributes of unlogged forest. Despite the passage of 45 years, the legacy of selective logging on the tree community in Kibale National Park is still evident, as indicated by distinct taxonomic and structural composition and reduced carbon storage in logged forest compared with unlogged forest. The effects of selective logging are exerted via influences on tree demography rather than functional trait composition.
... The classification of predominantly F or H was based on published descriptions of animal species' diets (Oates 1977;Rudran 1978;Olupot 1998;Chapman et al. 2002;Stickler 2004;Rode et al. 2006;Struhsaker 2017) and extensive observation and sampling of dung (CAC unpublished data). The potential effects of elephants and the primates on forest dynamics are clearly documented (Wing and Buss 1970;Oates 1977;Rudran 1978;Olupot 1998;Chapman et al. 2002;Stickler 2004;Rode et al. 2006;Omeja et al. 2014). However, these effects are not so clear for less well-known duikers, bushbuck, and bushpigs. ...
... In addition, we expected that tree species preferred by elephants would change in abundance with changes in elephant numbers as elephants would be killed them either because by pushing them over or debarking them. The species preferred by elephants were determined from several studies (Kasenene 1980;Kasenene 1984;Kasenene 1987;Lwanga 1994;Struhsaker et al. 1996;Omeja et al. 2014). To quantify elephant feeding preferences their tree species selection ratio was calculated (for details of the calculation see Omeja et al. 2014). ...
... The species preferred by elephants were determined from several studies (Kasenene 1980;Kasenene 1984;Kasenene 1987;Lwanga 1994;Struhsaker et al. 1996;Omeja et al. 2014). To quantify elephant feeding preferences their tree species selection ratio was calculated (for details of the calculation see Omeja et al. 2014). A ratio greater than one indicates the species was selectively browsed. ...
Article
Full-text available
Background Tropical forests are repositories of much of the world’s biodiversity and are critical for mitigation of climate change. Yet, the drivers of forest dynamics are poorly understood. This is in large part due to the lack of long-term data on forest change and changes in drivers. Methodology We quantify changes in tree abundance, diversity, and stand structure along transects first enumerated in 1978 and resampled 2019 in Kibale National Park, Uganda. We tested five predictions. First, based on the purported role of seed dispersal and herbivory and our quantification of changes in the abundance of frugivores and herbivores, we tested two predictions of how faunal change could have influenced forest composition. Second, based on an evaluation of life history strategies, we tested two predictions concerning how the forest could have changed following disturbance that happened prior to written history. Finally, based on a 50-year climate record, we evaluate the possible influence of climate change on forest dynamics. Results More trees were present on the assessed transects in 2019 (508) than in 1978 (436), species richness remained similar, but diversity declined as the number of dominant species increased. Rainfall increased by only 3 mm over the 50 years but this had not significant effect on forest changes measured here. Annual average monthly maximum temperature increased significantly by 1.05 °C over 50 years. The abundance of frugivorous and folivorous primates and elephants increased over the 50 years of monitoring. Neither the prediction that an increase in abundance of seed dispersing frugivores increases the abundance of their preferred fruiting tree species, nor that as an increase in folivore abundance causes a decline in their preferred species were supported. As predicted, light-demanding species decreased in abundance while shade-tolerant species increased as expected from Kibale being disturbed prior to historical records. Finally, while temperature increased over the 50 years, we found no means to predict a priori how individual species would respond. Conclusions Our study revealed subtle changes in the tree community over 40 years, sizable increases in primate numbers, a substantial increase in the elephant population and an increase in local temperature. Yet, a clear picture of what set of interactions impact the change in the tree community remains elusive. Our data on tree life-history strategies and frugivore/herbivore foraging preferences suggest that trees species are under opposing pressures.
... The encounter rate of black and white colobus in the heavily-logged area initially increased right after logging, but then declined thereafter; however, to levels still higher than those immediately recorded in the earliest record (1980). This initial increase likely happened because black and white colobus could feed on the largely undefended young leaves of fast growing pioneer species (e.g., Trema orientalis), that rapidly establish after logging, but were replaced in the 1990s by less palatable herbaceous species such as Acanthus pubescens Omeja et al. 2014). Of all the species, black and white colobus thrive in heavily-logged areas (Struhsaker 1975;Skorupa 1988;Struhsaker 1997). ...
... However, our data provides an opportunity to see how the park has changed in the last 40 + years and can help predict future biodiversity conservation issues. These populations have been affected by many changes including: logging that resulted in decreased food availability and compression caused by animals moving away from the disturbed areas Osazuwa-Peters et al. 2015a, b), the disappearance of fragments outside of the park and the immigration of animals into Kibale (Chapman et al. 2013b), climate change , exponentially rising elephant numbers impacting vegetation (Omeja et al. 2014), changing forest tree community structure (Chapman et al. 2010a;Omeja et al. 2012), and the impact of invasive plant species (Lantana camera) . None of these processes are likely to have a linear affect, they will change at different rates, and the processes will likely combine in unexpected ways. ...
... This puts great pressure on the parks as the people living next to the park boundary are poor and resources are difficult to find (Naughton et al. 2011;MacKenzie et al. 2017). Recently the elephant population in Kibale have increased substantially (Omeja et al. 2014;Mondol et al. 2015;Omeja et al. 2016), partially as a result of immigration from the Democratic Republic of Congo (Keigwin et al. 2016), and since these animals are predominantly found within the forest and elephants can damage forest ecosystems, the success with elephant conservation may become a problem for primate conservation in the near future. To manage changes in threats like these and new ones that will arrive (e.g., climate change, introduced species like Lantana camera), continued monitoring and modification of conservation plans are needed. ...
Article
Full-text available
The rapid disappearance of tropical forests, the potential impacts of climate change, and the increasing threats of bushmeat hunting to wildlife, makes it imperative that we understand wildlife population dynamics. With long-lived animals this requires extensive, long-term data, but such data is often lacking. Here we present longitudinal data documenting changes in primate abundance over 45 years at eight sites in Kibale National Park, Uganda. Complex patterns of change in primate abundance were dependent on site, sampling year, and species, but all species, except blue monkeys, colonized regenerating forest, indicating that park-wide populations are increasing. At two paired sites, we found that while the primate populations in the regenerating forests had increased from nothing to a substantial size, there was little evidence of a decline in the source populations in old-growth forest, with the possible exception of mangabeys at one of the paired sites. Censuses conducted in logged forest since 1970 demonstrated that for all species, except black-and-white colobus, the encounter rate was higher in the old-growth and lightly-logged forest than in heavily-logged forest. Black-and-white colobus generally showed the opposite trend and were most common in the heavily-logged forest in all but the first year of monitoring after logging, when they were most common in the lightly-logged forest. Overall, except for blue monkey populations which are declining, primate populations in Kibale National Park are growing; in fact the endangered red colobus populations have an annual growth rate of 3%. These finding present a positive conservation message and indicate that the Uganda Wildlife Authority is being effective in managing its biodiversity; however, with constant poaching pressure and changes such as the exponential growth of elephant populations that could cause forest degradation, continued monitoring and modification of conservation plans are needed.
... The limited duration of field studies increases the uncertainty in their results. There is a lack of long-term tropical forest inventories with data covering multiple decades, except for a few notable sites such as Kibale National Park in Uganda and Barro Colorado Island in Panama (Wright et al. 2000, Omeja et al. 2014). In addition, it is difficult to find comparable regions (similar adult tree composition, disturbance history, and environmental conditions) with different defaunation histories, and to regularly monitor forest regeneration without sufficient long-term funding. ...
... In particular, there is a research gap concerning the physical impacts (ecosystem engineering) of megafauna in tropical forests. Studies of both African forest and Asian elephants Elephas maximus, and of Asian water buffalo Bubalus bubalis have shown that megafauna can influence plant composition and diversity, and forest structure (Braithwaite et al. 1984, Pradhan et al. 2007, Ssali et al. 2013, Terborgh et al. 2016, although, no effects on species composition have been reported in some cases (Omeja et al. 2014). Forest elephants can also inhibit forest regeneration and increase understory openness. ...
... Forest elephants can also inhibit forest regeneration and increase understory openness. However, these processes might be interlinked with natural and human disturbances (Lawes and Chapman 2006, Inogwabini et al. 2013, Omeja et al. 2014. Megafauna can change competition among plants by modifying light, water, nutrients, and soil properties favoring certain plant species or life strategies. ...
Article
Full-text available
Megafauna (terrestrial vertebrate herbivores > 5kg) can have disproportionate direct and indirect effects on forest structure, function, and biogeochemical cycles. We reviewed the literature investigating these effects on tropical forest dynamics and biogeochemical cycles in relation to ecology, paleoecology, and vegetation modelling. We highlight the limitations of field‐based studies in evaluating the long‐term consequences of loss of megafauna. These limitations are due to inherent space‐time restrictions of field‐studies and a research focus on seed dispersal services provided by large animals. We further present evidence of a research gap concerning the role of megafauna in carbon cycling in tropical ecosystems. Specifically, changes in aboveground biomass might not be noticeable in short‐term studies because of slow vegetation dynamics requiring decades to respond to disturbance (i.e., defaunation). Nutrient cycling has received even less attention in relation to the role of megafauna in tropical forests. We present an approach to investigate the effects of megafauna from new perspectives and with various tools (notably, vegetation models) which can simulate long‐term dynamics in different environmental and megafauna density scenarios. Vegetation models could facilitate interaction between plant‐animal ecology and biogeochemistry research. We present practical examples on how to integrate plant‐animal interactions in vegetation models to further our understanding of the role of large herbivores in tropical forests. This article is protected by copyright. All rights reserved.
... This relationship is still evident today in tropical forests. Changes in seed dispersal success (136), seedling recruitment (137), and sapling recruitment (138) have already been linked to frugivore declines in Central Africa (139,140) and in turn to decreases in carbon storage (141). However, diminished seed dispersal, particularly for long-lived trees with a large number of dispersers, could be less relevant than the increased sapling choking and understory thickening, which also occurs when browsers such as elephants or gorillas are lost. ...
... However, diminished seed dispersal, particularly for long-lived trees with a large number of dispersers, could be less relevant than the increased sapling choking and understory thickening, which also occurs when browsers such as elephants or gorillas are lost. On the other hand, severe sapling browsing by elephants may inhibit recruitment, even when seed dispersal is high (139,142). Grasping the significance of rapid changes in animal populations has placed defaunation prominently on the list of critical anthropogenic factors in environmental issues for the region, but although we understand that trophic change is in motion, for many plant and animal species in Central Africa direct mortality from land conversion or hunting will alter populations, possibly eradicating them, far faster than declines from reduced ecological success. ...
... Available data on liana growth and geographic range suggest that high liana abundance and competitive vigour (and hence also non-linear forest recovery pathways) are most feasible in moist forests (Durán et al., 2015) under high seasonality and long dry season length (DeWalt et al., 2015;Schnitzer, 2018) and local scale disturbance-induced increases in water stress and light (Capers et al., 2005;Dupuy and Chazdon, 2006;Jirka et al., 2007;Schnitzer and Bongers, 2011;Magnago et al., 2017). In addition, liana growth and/or abundance correlate positively with elevated CO 2 (Granados and Körner, 2002), windspeed (Magnago et al., 2017) and probably also mammal herbivory (Omeja et al., 2014;Luskin et al., 2019) and fire (Gerwing, 2001) although findings are inconsistent (Wright et al., 2007;Balch et al., 2011). Recent data, whilst limited (Fadrique and Homeier, 2016), show a positive influence of soil fertility on liana growth relative to trees (Lai et al., 2017). ...
... Similarly, disturbance to forest canopies is often accompanied by other forms of potential disturbance feedbacks, including defaunation from hunting that removes a functional component vital for recovery, further impairing seed predation and dispersal (Wright et al., 2007). Conversely, in the absence of hunting, canopy disturbance may instigate feedbacks from large animals, e.g., savanna elephants and pigs, that appear to maintain open canopy forest suitable for lianas (Marshall et al., 2012;Omeja et al., 2014;Luskin et al., 2019). ...
Article
Full-text available
Lianas are woody vines, rooted in the soil, and supported physically by trees. Lianas contribute to forest ecosystem functioning globally, but especially in the tropics and subtropics. However, prolific liana growth following heavy disturbance frequently affects subsequent recovery of forest tree diversity, biomass, structure, and function. Understanding this forest liana dynamic, and its sensitivity to climate and anthropogenic forces, is essential for worldwide forest restoration and climate change mitigation. Here, we synthesise the evidence for both positive and negative effects of lianas on forests and propose a framework that outlines the expected global response of forests to disturbance-induced liana proliferation. Emerging evidence suggests that lianas play a major role in both facilitating and delaying forest recovery following disturbance. At low levels of disturbance and/or where environmental conditions favour tree growth, lianas can facilitate forest recovery by protecting trees from extreme weather, fire, weed invasion and herbivory. However, under conditions where lianas proliferate beyond critical thresholds, positive feedbacks are expected to induce and sustain liana-dominated forest states that can endure for decades or even longer. We conceptualise alternative classes of forest recovery response to disturbance and describe measurement and modelling of liana thresholds.We identify four essential challenges for global change science relating to lianas: (1) incorporation of lianas and sapling stems into forest monitoring and tree stand measurements worldwide; (2) long-term experiments to determine variation in liana-tree competition, and potential drivers across forest successional gradients; (3) identification and prediction of liana thresholds and other alternative forest recovery response classes; and (4) dynamicmechanisticmodelling of forest recovery to determine regional and global variation within and among different recovery response classes, in relation to variation in potential drivers, liana feedbacks and their interactions. Addressing these challenges will determine the importance of lianas in shaping regional and global forest composition, recovery and dynamics.
... The change in primate abundance was complex with the magnitude of change dependent on site and species. Primate populations were affected by logging, changes in food availability, increased diffuse competition from animals fleeing disturbed areas (Chapman, Balcomb, Gillespie, Skorupa, & Struhsaker, 2000;Osazuwa-Peters, Chapman, & Zanne, 2015;Osazuwa-Peters, Jime´nez, Oberle, Chapman, & Zanne, 2015), climate change (Chapman, Hou, & Kalbitzer, Submitted;Rothman et al., 2015), exponentially rising elephant numbers disturbing vegetation (Omeja et al., 2014), changing forest tree community structure (Chapman et al., 2010;Omeja, Obua, Rwetsiba, & Chapman, 2012), and invasive plant species (Lantana camera; Omeja et al., 2016). None of these processes had a strictly linear affect; they caused change at different rates with different and sometimes unexpected synergies between them. ...
... Long-term monitoring also often produces surprises. For example, the slow population decline and reduced distribution of blue monkeys (Chapman et al., 2018), the dramatic increase in population size of elephants (Omeja et al., 2014), or the foraging by folivorous primates can alter the composition of the tree community (Chapman et al., 2013),-none of this would have been detected without long-term monitoring in Kibale. ...
Article
Full-text available
In much of the tropics, the proportion of the land covered by regenerating forest surpasses than in primary forest, thus protecting regenerating forest could offer a valuable conservation opportunity, but only if those lands promote faunal recovery. Chapman et al. documented the recovery of populations of six primate species over up to 45 years in Kibale National Park, Uganda and discovered that in preexisting forest, populations of all species grew, except blue monkeys. Populations (except blue monkeys) also increased by colonizing regenerating forests at previously cleared sites. In many cases, populations in these regenerating areas were of comparable size to those in old-growth forest, and there was little evidence that this population increase corresponded with a decline in neighboring old-growth forests. This research demonstrates the potential for management of regenerating forest to be an effective conservation tool and illustrates the importance of conducting and funding long-term monitoring.
... Available data on liana growth and geographic range suggest that high liana abundance and competitive vigour (and hence also non-linear forest recovery pathways) are most feasible in moist forests (Durán et al., 2015) under high seasonality and long dry season length (DeWalt et al., 2015;Schnitzer, 2018) and local scale disturbance-induced increases in water stress and light (Capers et al., 2005;Dupuy and Chazdon, 2006;Jirka et al., 2007;Schnitzer and Bongers, 2011;Magnago et al., 2017). In addition, liana growth and/or abundance correlate positively with elevated CO 2 (Granados and Körner, 2002), windspeed (Magnago et al., 2017) and probably also mammal herbivory (Omeja et al., 2014;Luskin et al., 2019) and fire (Gerwing, 2001) although findings are inconsistent (Wright et al., 2007;Balch et al., 2011). Recent data, whilst limited (Fadrique and Homeier, 2016), show a positive influence of soil fertility on liana growth relative to trees (Lai et al., 2017). ...
... Similarly, disturbance to forest canopies is often accompanied by other forms of potential disturbance feedbacks, including defaunation from hunting that removes a functional component vital for recovery, further impairing seed predation and dispersal (Wright et al., 2007). Conversely, in the absence of hunting, canopy disturbance may instigate feedbacks from large animals, e.g., savanna elephants and pigs, that appear to maintain open canopy forest suitable for lianas (Marshall et al., 2012;Omeja et al., 2014;Luskin et al., 2019). ...
Article
Full-text available
Lianas are woody vines, rooted in the soil and supported physically by trees. Lianas contribute to forest ecosystem functioning globally, but especially in the tropics and subtropics. However, prolific liana growth following heavy disturbance frequently affects subsequent recovery of forest tree diversity, biomass, structure and function. Understanding this forest liana dynamic, and its sensitivity to climate and anthropogenic forces, is essential for worldwide forest restoration and climate change mitigation. Here, we synthesise the evidence for both positive and negative effects of lianas on forests and propose a framework that outlines the expected global response of forests to disturbance-induced liana proliferation. Emerging evidence suggests that lianas play a major role in both facilitating and delaying forest recovery following disturbance. At low levels of disturbance and/or where environmental conditions favour tree growth, lianas can facilitate forest recovery by protecting trees from extreme weather, fire, weed invasion and herbivory. However, under conditions where lianas proliferate beyond critical thresholds, positive feedbacks are expected to induce and sustain liana-dominated forest states that can endure for decades or even longer. We conceptualise alternative classes of forest recovery response to disturbance and describe measurement and modelling of liana thresholds. We identify four essential challenges for global change science relating to lianas: (1) incorporation of lianas and sapling stems into forest monitoring and tree stand measurements worldwide; (2) long-term experiments to determine variation in liana-tree competition, and potential drivers across forest successional gradients; (3) identification and prediction of liana thresholds and other alternative forest recovery response classes; and (4) dynamic mechanistic modelling of forest recovery to determine regional and global variation within and among different recovery response classes, in relation to variation in potential drivers, liana feedbacks and their interactions. Addressing these challenges will determine the importance of lianas in shaping regional and global forest composition, recovery and dynamics.
... Howard et al. (1999) reported elephants in Itwara, but we found neither camera evidence nor direct observations of elephant activity. Future research should investigate whether this is because Itwara is inhospitable to elephants or whether Kibale National Park draws elephants away (Omeja et al., 2014). Buffalo, L'Hoest's monkey, Peters's duiker, bushbuck and the giant forest hog also F I G U R E 1 Box a: Study site and location of Ugandan protected areas (shaded in green). ...
... These two species were likely eradicated or drawn away from Itwara. Elephant populations in neighbouring PAs, especially Toro-Semliki Wildlife Reserve and Kibale National Park, are increasing dramatically though (Omeja et al., 2014). ...
... The villages bordering the park suffer crop raiding by park animals Mackenzie and Ahabyona 2012) and are not compensated by the government because compensation for crop raiding is prohibited by the Wildlife Act for Uganda (Hartter 2009) and because of the logistical and financial difficulties of compensation. While the impact of different crop raiding animals has changed overtime (MacKenzie et al. 2017), elephants and baboons (Papio anubis) are currently considered large problems ) see below) and elephant populations have increased exponentially in Kibale (Omeja et al. 2014;Omeja et al. 2016). ...
... Stratified random sampling first based on distance from the park boundary was used to select villages. Studies on crop-raiding in the region found that farms closer to the park boundary are more susceptible to crop raiding (Naughton-Treves 1998;Omeja et al. 2014). Similarly, elephant crop damage is confined to <200m of the park boundary (Rode et al. 2006). ...
Article
Full-text available
It is widely viewed that by providing employment or services to neighbouring communities, a protected area may increase positive attitudes towards conservation and discourage encroachment, but this is rarely tested. Our research examines this view by evaluating local attitudes towards the park and incidence of encroachment before and after the implementation of a novel conservation strategy – a mobile health clinic - in the predominantly agricultural communities bordering Kibale National Park, Uganda. The implementation of the mobile clinic programme coincided with a more positive attitude towards the park and a decrease in the number of people who 'disliked' the park. Despite this, the incidence of encroachment increased. There are a number of possible explanations for this contradiction, including respondents giving answers they believe will maintain the service they appreciate, and that while the local community may appreciate the mobile clinic, this appreciation is not sufficient to make people alter their behaviour because of tradition or need (e.g., the need among the very poor to feed their family or send a child to school is very high). Overall, people typically expressed that they did not have a problem with living adjacent to the park, except for the harm done by crop-raiding animals. However, local people expressed the view that they receive few benefits from the park – a perception that might be improved with more extensive use of the mobile clinic.
... An alternative explanation is that there are multiple forest-wide perturbations simultaneously operating on the vegetation in Kibale independent of the selective logging event 45 years ago. Three main sources of forest-wide disturbance in Kibale have been reported including changing rainfall patterns (Hartter et al., 2012), concentrated elephant abundance and activities (Omeja et al., 2014), and intense competition from non-tree vegetation (Duclos et al., 2013). Synergistic interactions among multiple perturbations are thought to result in long-term changes in fundamental aspects of the structure and function of biological communities (Paine et al., 1998). ...
Conference Paper
Background/Question/Methods: The disturbance-recovery hypothesis posits that current structural changes in tropical forests, such as increasing stem density and biomass, are due to successional recovery from past disturbances. This hypothesis has typically been tested using taxon analyses to assess increases in abundance of shade-tolerant or late-successional species. Here, we focus on testing the prediction that community change (turnover) decelerates during succession as the community recovers from disturbance and stability increases. Further, we expect that the rate of deceleration in turnover will be greater for a recently disturbed forest relative to an undisturbed forest. To test these predictions, we compare magnitude of turnover and rate of change in turnover in stem number, species composition, and functional composition of forest that was selectively logged 46 years ago to an adjoining undisturbed old-growth forest. Our analysis is based on functional trait data related to carbon storage capacity (wood density, maximum height and maximum diameter at breast height), as well as abundance data from four censuses spaced over 24 years (1989 – 2013) for 26 plots totaling 5.2 ha in Kibale National Park, Uganda. Results/Conclusions: Rates of change in turnover did not decelerate through time in any of the three community attributes irrespective of plot logging status. Instead, rates of change in turnover for stem number and species composition accelerated while turnover in functional composition showed no temporal changes. However, selectively logged plots showed greater turnover in stem number with slower acceleration, as well as greater turnover in species composition than unlogged plots. Our results do not support the disturbance-recovery hypothesis as an explanation of change in Kibale forest as we do not find the reduced change through time predicted for communities recovering from disturbance. Although disturbance (selective logging) seems to have affected the magnitude of turnover in stem number and species composition, it had little effect on temporal patterns of change. Since, both selectively logged forest and undisturbed forest showed increasing rates of change, we suggest that there is a forest-wide synchronous driver of change unrelated to the disturbance event of selective logging 46 years ago. While our results are consistent with reports of global-scale temporal changes in tropical forests, they raise further questions about the direction and drivers of turnover in Kibale forest.
... An alternative explanation is that there are multiple forest-wide perturbations simultaneously operating on the vegetation in Kibale independent of the selective logging event 45 years ago. Three main sources of forest-wide disturbance in Kibale have been reported including changing rainfall patterns (Hartter et al., 2012), concentrated elephant abundance and activities (Omeja et al., 2014), and intense competition from non-tree vegetation (Duclos et al., 2013). Synergistic interactions among multiple perturbations are thought to result in long-term changes in fundamental aspects of the structure and function of biological communities (Paine et al., 1998). ...
... Though highly controversial, the introduction of a functional analogue such as elephants (Elaphas maximus or Loxodonta africana) to South American forests with megafaunal fruits might restore tree regeneration patterns (e.g. Galetti, 2004;Blake et al., 2009;Haddad et al., 2009;Omeja et al., 2014;Asner et al., 2016), along with other ecological functions presumably also associated with gomphotheres, giant sloths, and perhaps other herbivorous megafauna (Galetti et al. in review). An exciting opportunity to test the role of elephants as megafauna surrogates in South America is a recently established sanctuary for elephants in Brazil, where 1100 ha of savanna will be designated for the well-being of formerly captive elephants (globalelephants.org). ...
Article
Full-text available
There are various approaches to rewilding, corresponding to different socio-ecological and policy contexts. Most South American ecosystems have experienced Pleistocene and historical defaunation and the functional persistence of many areas will depend on restoration and rewilding. Rewilding is not seen as a priority or as a tool for restoration in South America, but we argue that several concepts could potentially be adapted to their contexts to respond flexibly to developing socio-ecological conditions. Here, we consider 10 questions that rewilding projects should consider, and we provide examples of how these questions are relevant to South America and how they have been answered already, in some cases. The 10 questions include: What role should humans play in rewilding projects? How can society deal with "monsters"? Is there a rationale for non-analogue rewilding? How do we justify baselines? Is it possible to do rewilding with small species? What is the right scale for a rewilding project? Should rewilding projects worry about sample size and pseudo-replication? When should we rewild carnivores? Do we need to distinguish rewilding from safari parks and zoos? What should be included in integrated monitoring and assessment? The questions we raise here do not have general answers optimal for all situations, but should be answered with reference to the socio-ecological conditions and transformational possibilities in different areas of South America.
... Elephant and rhinoceros damage trees (Schüle, 1992;Omeja et al., 2014;Terborgh et al., 2016) Large scale deforestation to gain forage areas for domestic herbivores and crop fields (Godwin, 1944;Williams, 2008) Nutrient cycling and fertilization Recycling and spreading of nutrients away from hotspots and counteracting gravity Doughty et al., 2013Doughty et al., , 2016b Active fertilization of agricultural areas: manuring, plowing, cultivation of legumes in rotation (Galloway et al., 2013); recycling human and animal waste (Melillo, 2012); increasing P export (Boyle et al., 2015) Megafruit and seed dispersal Promoting dispersal of plants with megaseeds (Guix, 2009;Corlett, 2013) Domestication of megafruit plant species (e.g., avocado, chocolate, squashes Kistler et al., 2015) Emissions of greenhouse gas Methane emissions through digestive fermentation (Smith et al., 2016a) CO 2 emissions through forest clearing (Ruddiman and Ellis, 2009). Methane emissions by domestic ruminants, rice paddies (Fuller et al., 2011) In some cases, humans have limited the negative impact of the loss of megaherbivores for the plant species producing very large fruits and they behaved as a partial replacement of large fruits dispersers (Guimarães et al., 2008). ...
Article
Full-text available
Megaherbivores fulfilled a number of important ecological functions in terrestrial ecosystems and behaved as ecological engineers since 300 million years until around 12,000 years ago. These essential ecological functions include opening vegetation cover, selective seed dispersal and nutrient recycling and spreading. Thanks to these effects, megaherbivores change the vegetation structure where they live, with cascading effects on smaller herbivores and also on climate. The late Pleistocene extinction strongly impacted the megaherbivores almost all over the world and led to the loss of these important ecological functions in terrestrial ecosystems. These functions were partially restored by agriculturist humans through an ecological replacement that occurred through an ecological shift within the species Homo sapiens. A better understanding of the differences and similarities between the ecological impacts of megaherbivores and those of agricultural humans should help to predict the future of terrestrial ecosystems.
... The outcome of such conservation efforts is, however, not always predictable because other factors, such as climate and the immigration of competitors (e.g. elephants; Omeja et al. 2014Omeja et al. , 2016, can change, and different species of primates respond in different ways to habitat regeneration Jack 2001, 2012;). ...
Chapter
Most primate habitats are undergoing intense and rapid changes due to anthropogenic influences resulting in many primate populations being threatened. Habitat loss and fragmentation are already extensive; thus dispersal to unoccupied habitats is an unlikely adaptive response to these changes. Furthermore, most primates have slow life histories and long generation times, and because environmental change is occurring at an unprecedented rate, gene-based adaptations are also unlikely to evolve fast enough to offer successful responses to these changes. However, long primate life histories are linked to well-developed brains, which may allow primates to respond to environmental change through behavioural flexibility. Here we ask: What are the most common challenges of changing environments for primates and what do we know about their behavioural abilities to respond to such changes? To answer this question, we first review the most common types of habitat/landscape alterations, the extent of human-primate interactions, and the impact of climate change. Next, we evaluate how primates respond to these changes via behavioural flexibility, and using different approaches and datasets, we discuss how to investigate if these responses are beneficial with regard to population persistence. Finally, we discuss how comparisons across species, space, and time can be used to draw generalizations about primate responses to environmental change while considering their behavioural flexibility and the data derived from case studies. We demonstrate how understanding behavioural flexibility as a response to environmental change will be crucial to optimize conservation efforts by constructing informed management plans.
... Forest elephant populations are being decimated across much of Central Africa (Maisels et al. 2013, Poulsen et al. 2017, while in a few protected forested areas, like Kibale, where they are likely seeking refuge, their numbers are increasing rapidly (Omeja et al. 2014). It is therefore critical that the scientific community provides information on their role in forest ecosystems as they are a clear example of ecosystem engineers (Chapman et Table 1. ...
Article
Megaherbivores play a central role in the evolution and functioning of ecosystems. In tropical forests elephant species are some of the few remaining megaherbivores. Through elephant foraging, nutrients that would be locked in leaves and stems, taking months or years to decay, are quickly liberated for use. In 10 experimental sites in Kibale National Park, Uganda, we set up 10 pairs of plots (4 × 4 m), each pair involved one treatment, elephant dung addition, and one control. After 1 y, we quantified growth (height and leaf number) and survival of young light-demanding (12) and shade-tolerant (19) plant species (439 stems in total). In general, the addition of elephant dung did not increase seedling growth, and it only increased the number of leaves in shade-tolerant plants with a large initial number of leaves. Researchers have speculated that the loss of elephants would shift the composition of African forests to slow-growing tree species. However, this is not supported by our finding that shows some slow-growing shade-tolerant plants grew more new leaves with additional nutrient input from elephant dung, a condition that would occur if elephant numbers increase.
... Note that this kind of growth is the classical behaviour in branching processes including the Galton-Watson predator-prey process (see [1]), but it is not typical in predator-prey systems modelled through ODEs, where periodic cycles are observed. However, there are examples of populations with this exponential growth behaviour (see [43], [42], [37], [45] or [3]). Moreover, our model can be also applied at initial stages of other populations when there is a small number of individuals, such as, for example, in populations of endangered species where the exponential growth is shown (see [26], [21] or [29]). ...
Preprint
In this paper, we introduce a two-sex controlled branching model to describe the interaction between predator and prey populations with sexual reproduction. This process is a two-type branching process, where the first type corresponds to the predator population and the second one to the prey population. While each population is described via a two-sex branching model, the interaction and survival of both groups is modelled through control functions depending on the current number of individuals of each type in the ecosystem. We provide necessary and sufficient conditions for the ultimate extinction of both species, the fixation of one of the species and the coexistence of both of them. Moreover, the description of the present predator-prey two-sex branching process on the fixation events can be performed in terms of the behaviour of a one-type two-sex branching process with a random control on the number of individuals, which is also introduced and analysed.
... Generally, forest elephants inhibit the growth of young saplings and reduce the diversity of large ones (Terborgh et al., 2016), whilst being more efficient seed dispersers than their savannah counterparts (Campos-Arceiz and Blake, 2011;Yumoto et al., 1995). In terms of forest succession, their presence can inhibit forest regeneration and maintain forest gaps (Omeja et al., 2014). Preferential browsing of forest elephants also repetitively maintains bare ground and their trampling repeatedly destroys seeds and small saplings (Terborgh et al., 2016). ...
Thesis
Biodiversity patterns of butterflies and moths are investigated on the southwestern slope of Mount Cameroon, the only continuous elevational gradient of near-pristine forests in the Afrotropics. Three distinct seasons between 2014 and 2017 are sampled by two standardised methodologies (i.e., bait-trapping and manual catching of selected groups of moths at light). First, the effects of seasonality and forest habitat associations on butterflies and moths are investigated in the lowland rainforest. Then, the impacts of elephant-made natural disturbances on tree, butterfly, and moth diversities at mid-elevations is evaluated. The thesis also includes faunistic records of species never reported from the area, combining them with life history notes on selected taxa and species description of nine new species of Alucita. Finally, the last chapter focuses on the biodiversity of birds, trees, and butterflies in the last large patch of coastal forest of the studied area, and discusses its current conservation status.
... We found a consistent intercontinental difference in HMax across biomes (Figure 1; Table 2). We did not interpret this pattern as a direct result of disturbance by megaherbivores, because empirical evidence that large mammals, such as elephants, substantially affect tree demography in forest is equivocal (Cardoso et al., 2019;Omeja et al., 2014). Instead, because fruit size and HMax are positively correlated , the height differentiation shown here is more consistent with a reduced Neotropical stock and distribution of large-fruited plants owing to the extinction and lower pre-extinction historical diversity of megadispersers ( Figure 3). ...
Article
Aim Biomes can diverge substantially in plant functional traits and disturbance regimens among regions. Given that Neotropical and Afrotropical regions have contrasting histories of the megafauna (because of the Holocene megafaunal extinction in the Neotropics), we hypothesize that they should harbour plants with different traits in relationship to herbivory and fire, especially in savannas. We predicted that herbivory resistance traits should be more prominent in Afrotropical savanna plants and fire resistance in Neotropical savanna plants. Location Tropics. Time period Not applicable. Major taxa studied Angiosperms (woody). Methods We compiled data for five key plant functional traits (wood density, specific leaf area, maximum tree height, spinescence and proportion of geoxyles) for forest and savanna woody species from the two distant regions (Afrotropics and Neotropics). We related these data to climate, soil and fire variables and tested predictions for megafauna selection. Results Spines and high wood density were more common among Afrotropical than Neotropical savanna species and species from the two forests. Moreover, the Neotropical savanna region contained more geoxyles than the Afrotropical savanna region. Finally, Afrotropical species were taller than Neotropical species. These differences were consistent with our predictions for trait selection by the megafauna, and these patterns did not change when considering climate, soil and fire regimens in the models. Main conclusions Our results highlight the great potential of these traits for summarizing disturbance strategy axes in tropical woody species and suggest that global variation in plant traits is unlikely to be understood fully without consideration of historical factors, especially the direct and indirect impacts of megafauna.
... The processes that drive these transitions are still poorly understood, but they will probably be more widespread in the future, particularly in areas unsuitable for cropland and pasture intensification, such as the mountainous regions in our study cases. Nonetheless, ways of achieving these environmental benefits are hard to define (Svenning et al., 2016): the different pathways depicted here imply that dramatically different ecological outcomes might follow according to biophysical, social-ecological and landscape contexts: rapid rewilding is more likely to occur when native herbivore populations have persisted in well-connected habitats; but such rewilding may not necessarily result in increases in biodiversity or environmental services (Omeja et al., 2014); in fire-prone ecosystems, livestock reduction might result in increased fire frequency, with less predictable results, including maintenance of low-density livestock management whose compatibility with rewilding is unclear; in less connected habitats due to intensive agriculture or urbanization, recovery of native herbivores might be slower, likely resulting in major vegetation changes associated to gains in biomass. To understand and direct these transitions towards positive ecological outcomes, key factors to be addressed are the decision processes driving livestock decreasing intensity and the novel conflicts between and synergistic interactions between humans, livestock and wildlife ( Table 1). ...
Article
Full-text available
In most of the planet, large herbivore communities have been replaced by livestock, but this process is reversing in many places. Here, we outline and review the pathways of “megaherbivore rewilding transitions” in three social-ecological-systems of subtropical Argentina. In the extensive arid high-elevation Puna plateau we observed a “rapid rewilding pathway” where the reduction of livestock was accompanied by the recovery of native camelid populations from near extinction in a few decades. In the forest-grassland ecotone, decreasing livestock favored higher fire frequency, probably limiting the speed of native herbivore recovery in an “increasing fire pathway”. In lowland montane forests, the recovery of native herbivore communities appears to be lagged by fragmentation, local extinctions and human pressure, representing a case of “connectivity-limited rewilding”. These typologies exemplify the complexity of outcomes resulting from livestock diminishing density, and provide a framework to understand and optimize processes of large herbivore rewilding according to different social-ecological contexts.
... Overhunting and defaunation profoundly impact the ecological functioning of forest ecosystems (Redford, 1992). In particular, the extirpation of frugivore species has major ecological consequences (Beaune et al., 2013;Omeja et al., 2014) on seed dispersal (Haurez et al., 2015), forest regeneration (Poulsen et al., 2013;Vanthomme et al., 2010), and carbon storage (Brodie, 2016). Current declines in large mammal populations also strongly affect rural food security (Ziegler et al., 2016). ...
Thesis
Full-text available
Due to human-driven environmental changes, planet Earth has entered the new Anthropocene era, with major impact on biological diversity recognized as the sixth mass extinction period. The concepts of biodiversity and ecosystem services (ES) have risen to objectify and measure the human impacts on ecosystems and the many-fold contributions of ecosystems to human well-being. Among global terrestrial ecosystems, tropical forests are particularly important for the conservation of biodiversity and for the provision of ES. Agricultural conversion, logging, hunting, commercial poaching and over-harvesting lead to deforestation, degradation and defaunation of tropical forests, with highly variable consequences depending on many local factors. In Central Africa in particular, biodiversity and ES have been far less studied than in other tropical regions, despite the vital roles of these tropical forests in the livelihood of tens of millions of people in a context of high poverty. A better understanding of the determinants of biodiversity and ES in Central Africa is crucial for improving human well-being and the resilience of forest ecosystems. Despite the still relatively preserved tree cover across the region, biodiversity and ES may differ depending on forest land management and allocations. Therefore, the objective of this thesis is to assess the conservation value of tropical forests in southeastern Cameroon, as well as the supply of ES and use by local populations, in three contrasted forest allocations: a protected area, a Forest Stewardship Council (FSC)-certified logging concession, and three community forests. First, we assessed the conservation value of the three forest allocations, examining species richness and composition of two taxonomic groups: mammals inventoried with 44 camera traps, and dung beetles inventoried with 72 pitfall traps (Chapter 2). We also aimed to identify the determinants of forest conservation value, disentangling the effects of forest allocations, proximity to human settlements (villages and roads), and local forest habitat. Mammal and dung beetle species showed lower species richness in the community forests than in the protected area, and intermediate values in the logging concession. Proximity to human settlements and disturbance was negatively correlated to species richness of both groups, negatively correlated with species body size, and associated to the loss of the most threatened mammal species. The high species variability among forest allocations (i.e., spatial turnover) suggests that any conservation initiative should integrate many sites to protect a multitude of species, and not only large isolated areas. The high conservation value of the protected area has been confirmed, and the logging concession can play a complementary role in conservation strategies through landscape connectivity. In contrast, community forests are particularly defaunated due to their proximity to roads and villages, but they still provide wild proteins to local populations. Second, we assessed the perceptions of the supply of ES by tropical forests to local populations, and the determinants of these perceptions (Chapter 3). We evaluated the significance and abundance of ES by conducting a questionnaire survey with 225 forest stakeholders. The most significant ES perceptions were provisioning services (93% of respondents) and cultural services (68%), while regulating services were much less reported (16%). The perceptions of ES abundance were relatively homogeneous among forest allocations and respondents. Bushmeat provision has been identified as the only significant ES for local populations that is not supplied in high abundance. Third, we depicted the use of ES by local populations in three villages, and we evaluated its determinants and sustainability (Chapter 4). We used diverse interviews and field surveys to assess three provisioning services (bushmeat, firewood, and timber) and five cultural services (cultural heritage, inspiration, spiritual experience, recreation, and education). On average, local populations consumed 56 kg of bushmeat person–1 year–1 (hunting zones covering on average 213 km² per village), 1.17 m³ of firewood person–1 year–1 (collection zones on average 4 km² per village), and 0.03 m³ of timber person–1 year–1. On average, 59% of respondents recognized the importance of cultural services. The main determinants of ES use were forest allocations, population size, and deforestation rate, and we also showed slight differences between Baka and Bantu people in the use of cultural services. Firewood and timber have been shown to be used sustainably by local populations in this area, whereas bushmeat hunting and consumption have exceeded sustainability thresholds. Finally, the main findings of the thesis are summarized and their practical implications are discussed, in particular for the role of forest allocations (Chapter 5). The potential reconciliation between conservation and the sustainable use of tropical forests is discussed. Methodological feedbacks are given for the use of mammals and dung beetles as biodiversity indicators. Research perspectives are presented for a better understanding of the interactions between biodiversity and ES. Finally, different perspectives for integrating the concept of ES in tropical forest management are given: for instance, identifying and resolving conflicts among stakeholders, raising awareness, making decisions, or evaluating the effectiveness of conservation measures. In particular, ES are increasingly used in concrete management applications, such as FSC-certification, payments for environmental services, UNESCO Man and Biosphere Reserves, and various development projects.
... Note that this kind of growth is the classical behaviour in branching processes including the Galton-Watson predator-prey process (see [14]), but it is not typical in predator-prey systems modelled through ODEs, where periodic cycles are observed. However, there are examples of populations with this exponential growth behaviour (see [43,[45][46][47] or [48]). Moreover, our model can be also applied at initial stages of other populations when there is a small number of individuals, such as, for example, in populations of endangered species where the exponential growth is shown (see [49,50] or [51]). ...
Article
Full-text available
In this paper, we present the first stochastic process to describe the interaction of predator and prey populations with sexual reproduction. Specifically, we introduce a two-type two-sex controlled branching model. This process is a two-type branching process, where the first type corresponds to the predator population and the second one to the prey population. While each population is described via a two-sex branching model, the interaction and survival of both groups is modelled through control functions depending on the current number of individuals of each type in the ecosystem. In view of their potential for the conservation of species, we provide necessary and sufficient conditions for the ultimate extinction of both species, the fixation of one of them and the coexistence of both of them. Moreover, the description of the present predator–prey two-sex branching process on the fixation events can be performed in terms of the behaviour of a one-type two-sex branching process with a random control on the number of individuals, which is also introduced and analysed.
... The tropical forest of Central Africa is one of the richest regions of the world in terms of biodiversity (Malhi et al., 2013). This is largely due to the role that ecosystem engineers, such as forest duikers and elephants, play structuring and regenerating the forest (Feer 1989b;Wilkie et al., 2011;Omeja et al., 2014). Indeed, these medium size and large mammals represent an important component of the forest community, most of them being herbivores and frugivores. ...
Article
Full-text available
Central African duikers and elephants play a major role in seed dissemination, thus regenerating and structuring the forest. However, this forest mammal ecology is still poorly known, especially their diet. One possible explanation might be to gather field data and to experiment in a limited constrained environment. So, this study aimed to use a simple and efficient technique, seed germination, to determine central African forest duiker and elephant diet. A total of 43 fecal samples (34 duikers and 9 elephants) were collected in Lopé national park, central Gabon, and germinated into 96 pots containing either sterilized soil or cotton discs. Of the 96 germinating pots, 30 succeeded (31%) and 66 failed (69%); the highest germination success rate was recorded in soil (44%) and in elephant extracted seeds (33%) respectively. Furthermore, seven plant taxa were identified out of the germination experiment: Cesalpiniaceae, Lamiaceae, Loganiaceae, Melastomataceae, Rubiacaee, and two unidentified taxa. Of these, most germination success (23/30; 76,67%) were from the Rubiaceae family and more specifically from the savanna plant species Sarcocephaluslatifolius (Smith) Bruce(also known as Nauclea latifolia). Results of the present study proved to be useful as a first step in determining Central African duiker and elephant diet. However, these results should be further complemented with other techniques such as DNA metabarcoding or isotope analyses.
... To quantify elephant feeding preferences their tree species selection ratio was calculated (for details of the calculation seeOmeja et al. 2014). A ratio greater than one indicates the species was selectively browsed. ...
Preprint
Full-text available
Background: Tropical forests are repositories of much of the world’s biodiversity and are critical for mitigation of climate change. Yet, the drivers of forest dynamics are poorly understood. This is in large part due to the lack of longitudinal data on forest change and changes in drivers. Methodology: We quantify changes in tree abundance, diversity, and stand structure along transects first enumerated in 1978 and resampled 2019 in Kibale National Park, Uganda. We tested five predictions. First, based on the purported role of seed dispersal and herbivory and our quantification of changes in the abundance of frugivores and herbivores, we tested two predictions of how faunal change could have influenced forest composition. Second, based on an evaluation of life history strategies, we tested two predictions concerning how the forest could have changed following disturbance that happened prior to written history. Finally, based on a 50-year climate record, we test the possible influence of climate change on forest dynamics. Results: More trees were present on the assessed transects in 2019 (508) than in 1978 (436), species richness remained similar, but diversity declined as the number of dominant species increased. Rainfall increased by only 3 mm over the 50 years but this effect was not significant. Annual average monthly maximum temperature increased significantly by 2.2°C over 50 years. The abundance of frugivorous and folivorous primates and elephants increased over the 50 years of monitoring. The predictions that as the abundance of seed dispersing frugivores increases the abundance of their preferred fruiting tree species would increases and that as the abundance of folivorous would cause a decline in their preferred species were both not supported. Since Kibale was disturbed prior to historical records, we predicted that light-demanding species would decrease in abundance, while shade-tolerant species would increase - this was supported. Finally, while temperature increased over the 50 years, we found no means to predict a priori how individual species would respond. Conclusions: Our study revealed subtle changes in the tree community over 40 years, sizable increases in primate numbers, a substantial increase in the elephant population and an increase in local temperature. Yet, a clear picture of what set of interactions impact the change in the tree community remains elusive. Our data on tree life-history strategies and frugivore/herbivore foraging preferences suggest that trees species are under opposing pressures.
Article
Full-text available
The evolution of fruits contributed to the dominance of angiosperms and provided new ecological opportunities for frugivore vertebrates to diversify. However, it is not yet clear whether reciprocal coevolution between plants and frugivores drove the evolution of their mutualistic interactions. This review aimed at discussing major events of the evolution of fleshy-fruited angiosperms and their major seed dispersers, in order to elucidate if and how they responded to mutual selective pressures. Angiosperms evolved between the Mid and Late Cretaceous and they experienced a large diversification until the early Eocene. However, all main lineages of extant frugivores originated from the Eocene onward: frugivorous birds evolved in the Eocene but diversified in the Oligocene; primates evolved in the early Eocene and frugivorous bats diversified in the Oligocene-Miocene. This divergence in the times of the origins of angiosperm and their modern seed dispersers suggest that other animals interacted with early angiosperms. The most likely candidates are the rodent-like multituberculates. Several studies investigated how plant-frugivore mutualistic interactions contribute to the diversification in both plants and animals and we Oecologia Australis (ISSN: 2177-6199) Ahead of print (https 2 draw two main hypotheses from them: the plant-frugivore coevolutionary hypothesis and the neutral hypothesis. There are consistent evidences supporting each of these hypotheses, which suggest that they may not be mutually exclusives. An integrative approach is that plant-frugivore coevolution happens in pulses. Times of high environmental disturbances promote significant changes in mutualistic interactions and release new ecological opportunities for emerging species, which in turn exert stronger selective pressures and adaptive changes on fruit and frugivores traits. As evolving frugivores occupies those niches, interactions become more stable and coevolution is weaker and diffuse. We are currently undergoing a new period of unstable plant-frugivore interactions and we need more information on plant-frugivore coevolution in order to predict how species will respond to a changing world.
Article
Full-text available
Group size affects many aspects of the ecology and social organization of animals. We investigated group size stability for five primate species in Kibale National Park, Uganda from 1996 to 2011 at three nested spatial scales. Survey data indicated that group sizes did not change for most species, with the exception of red colobus monkeys (Procolobus rufomitratus), in which group size increased at all spatial scales. Mangabey (Lophocebus albigena) group size increased in old-growth forest, but the sample size and increase were small. To augment this survey data, we collected several years of demographic data on three habituated groups of redtail monkeys (Cercopithecus ascanius), eight groups of black-and-white colobus (Colobus guereza), and one red colobus group. The red colobus group increased from 59 to 104 individuals, while redtail monkey and black-and-white colobus group sizes were stable, mirroring our survey results. To understand mechanisms behind group size changes in red colobus versus stability in other primates, we monitored forest dynamics at two spatial scales between 1990 and 2013, considered changes in predator population, and explored evidence of disease dynamics. The cumulative size of all trees and red colobus food trees increased over 24 yr, suggesting that changing food availability was driving group size changes for red colobus, while predation and disease played lesser roles. Overall, our results and evidence of changing primate densities suggest that the Kibale primate community is in a non-equilibrium state. We suggest future conservation and management efforts take this into consideration.
Preprint
Full-text available
Megaherbivores have pervasive ecological effects. In African rainforests, elephants can increase aboveground carbon, though the mechanisms are unclear. Here we combine a large unpublished dataset of forest elephant feeding with published browsing preferences totaling > 120,000 records covering 700 plant species, including nutritional data for 102 species. Elephants increase carbon stocks by: 1) promoting high wood density tree species via preferential browsing on leaves from low wood density species, which are more digestible; 2) dispersing seeds of trees that are relatively large and have the highest average wood density among tree guilds based on dispersal mode. Loss of forest elephants could cause a 5-12% decline in carbon stocks due to regeneration failure of elephant-dispersed trees and an increase in abundance of low wood density trees. These results show the major importance of megaherbivores in maintaining diverse, high-carbon tropical forests. Successful elephant conservation will contribute to climate mitigation at a scale of global relevance.
Article
Full-text available
Poaching is rapidly extirpating African forest elephants (Loxodonta cyclotis) from most of their historical range, leaving vast areas of elephant-free tropical forest. Elephants are ecological engineers that create and maintain forest habitat, thus their loss will have strong consequences for the composition and structure of Afrotropical forests. We evaluated the roles of forest elephants in seed dispersal, nutrient recycling, and herbivory and physical damage to predict the cascading ecological effects of their population declines. Loss of seed dispersal by elephants will favor tree species dispersed abiotically and by smaller dispersal agents, with tree species composition depending on the downstream effects of changes in elephant nutrient cycling and browsing. Loss of trampling and herbivory of seedlings and saplings will result in high tree density as they are released from the pressures of browsing. Diminished seed dispersal by elephants and high stem density are likely to reduce the recruitment of large trees, resulting in a more homogeneous forest structure and decreased carbon stocks. In sum, the loss of ecological services by forest elephants will likely transform Central African forests to be more like Neotropical forests, from which megafauna were extirpated thousands of years ago. Without intervention, as much as 96% of Central African forests will have modified species composition and structure as elephants are compressed into remaining protected areas. Stopping elephant poaching is an urgent first step to mitigating these effects, but long-term conservation will require land use planning that incorporates elephant habitat into forested landscapes that are being rapidly transformed by industrial agriculture and logging.
Article
Full-text available
The Central African forests, the planet's second largest rainforest block, are key to global environmental health. They influence climate change through their crucial role in carbon sinking and storage, affect weather patterns across Africa, and safeguard unique species and biodiverse communities. Their fate is important to everyone, not just today's inhabitants. The forests cover seven countries, and the differing socioeconomic histories and trajectories of these nations determine divergent fates for people, trees, and wildlife across the region. We review current knowledge of how the Central African forests have been shaped by climate and human activity within the region and assess how they may evolve under future climate change, population growth, and the Anthropocene race for wealth and energy. We highlight three different environmental trajectories for the countries of the region, identify key current regional issues that have an international dimension, and highlight five new points of future concern.
Article
Tropical landscapes are changing rapidly as a result of human modifications; however, despite increasing deforestation, human population growth, and the need for more agricultural land, deforestation rates have exceeded the rate at which land is converted to cropland or pasture. For deforested lands to have conservation value requires an understanding of regeneration rates of vegetation, the rates at which animals colonize and grow in regenerating areas, and the nature of interactions between plants and animals in the specific region. Here, we present data on forest regeneration and animal abundance at four regenerating sites that had reached the stage of closed canopy forest where the average dbh of the trees was 17 cm. Overall, 20.3 percent of stems were wind-dispersed species and 79.7 percent were animal-dispersed species, while in the old-growth forest 17.3 percent of the stems were wind-dispersed species. The regenerating forest supported a substantial primate population and encounter rate (groups per km walked) in the regenerating sites was high compared to the neighboring old-growth forests. By monitoring elephant tracks for 10 yr, we demonstrated that elephant numbers increased steadily over time, but they increased dramatically since 2004. In general, the richness of the mammal community detected by sight, tracks, feces, and/or camera traps, was high in regenerating forests compared to that documented for the national park. We conclude that in Africa, a continent that has seen dramatic declines in the area of old-growth forest, there is ample opportunity to reclaim degraded areas and quickly restore substantial animal populations.
Article
Full-text available
Parks are essential for protecting biodiversity and finding ways to improve park effectiveness is an important topic. We contributed to this debate by examining spatial and temporal changes in illegal activities in Kibale National Park, Uganda between 2006 and 2016 and used existing data to evaluate how the changes were correlated with the living conditions of people in neighboring communities, as well as patrolling effort. We explore the effectiveness of conservation strategies implemented in Kibale, by quantifying changes in the abundance of nine animal species over two to five decades. While uncertainty in such animal survey data are inherently large and it is hard to generalize across a 795‐km2 area that encompasses diverse habitat types, data suggest an increase in animal abundance in the National Park. An increase in patrolling effort by park guards over the decade was correlated with a decline in the number of traps and snares found, which suggests patrolling helped limit resource extraction from the park. The park’s edge was extensively used for illegal forest product extraction, while the setting of snares occurred more often deeper in the forest. Perhaps counter‐intuitively, increased community wealth or park‐related employment in a village next to the park were positively correlated with increased illegal forest product extraction. Overall, our results suggest that the portfolio of conservation strategies used over the last two to five decades were effective for protecting the park and its animals, although understanding the impact of these efforts on local human populations and how to mitigate any losses and suffering they sustain remains an important area of research and action. It is evident that complex social, political and economic drivers impact conservation success and more interdisciplinary studies are required to quantify and qualify these dimensions. Finding ways to improve protected area effectiveness is a topic of importance. We contributed to this by examining spatial and temporal changes in illegal activities in Kibale National Park, Uganda between 2006 and 2016 and used existing data to evaluate how the changes were correlated with the living conditions of people in neighboring communities, as well as patrolling effort. We explore the effectiveness of conservation strategies implemented in Kibale, by quantifying changes in the abundance of nine animal species over two to five decades.
Article
Full-text available
Natural disturbances are essential for tropical forests biodiversity. In the Afrotropics, megaherbivores have played a key role before their recent decline. Contrastingly to savanna elephants, forest elephants' impact on ecosystems remains poorly studied. Few decades ago, forests on Mount Cameroon were divided by lava flows, not being crossed by a local population of forest elephants until now. We assessed communities of trees, butterflies and two guilds of moths in the disturbed and undisturbed forests split by the longest lava flow. We surveyed 32 plots, recording 2025 trees of 97 species, and 7853 insects of 437 species. The disturbed forests differed in reduced tree density, height, and high canopy cover, and in increased DBH. Forest elephants' selective browsing and foraging also decreased tree species richness and altered their composition. The elephant disturbance increased butterfly species richness and had various effects on species richness and composition of the insect groups. These changes were likely caused by disturbance-driven alterations of habitats and species composition of trees. Moreover, the abandonment of forests by elephants led to local declines of range-restricted butterflies. The recent declines of forest elephants across the Afrotropics probably caused similar changes in forest biodiversity and should be reflected by conservation actions.
Article
With a drastic decrease in their populations over the last decades, forest elephants Loxodonta cyclotis are facing increasing human pressure. Their decline will have serious ecological consequences, as they are key actors in shaping ecosystems. Whilst timber concessions host many mammal species, the interactions between selective logging and forest elephants remain unclear. Through an extensive literature review, we discussed the following: 1) the ecological and human factors that drive the distribution of forest elephants on a large scale as well as in the specific context of logged forests; 2) the contribution of forest elephants to the regeneration of timber species; and 3) the damage caused by forest elephants to timber species. Although human activities have the greatest impact on forest elephant distribution, it is the availability of food, water, and minerals that locally determines their use of the habitat. Under specific conditions, timber concessions may host large populations of forest elephants. As effective seed dispersers, forest elephants contribute to the regeneration of at least 41 timber species, such as Bobgunnia fistuloides (pao rosa), one of the most expensive woods on the market. Damage caused by forest elephants is diverse and affects a wide range of species. From branch breaking to bark stripping, at least 61 timber species are used by forest elephants, and little is known about the consequences for the tree's vitality and wood quality. The interactions between forest elephants and logging are complex and involve many variables, requiring additional research. Nevertheless, this review suggests that timber concessions constitute key areas for forest elephant conservation, provided that low‐impact logging and wildlife management are implemented. Avec une diminution drastique de leurs populations au cours des dernières décennies, les éléphants de forêt Loxodonta cyclotis font face à une pression humaine croissante. Jouant un rôle clé dans le façonnement des écosystèmes, leur déclin aura d'importantes conséquences écologiques. Alors que les concessions forestières abritent de nombreuses espèces de mammifères, les interactions entre l'exploitation sélective du bois d'œuvre et les éléphants de forêt restent floues. Par une revue approfondie de la littérature, nous avons examiné: 1) les facteurs écologiques et humains qui déterminent la distribution des éléphants de forêt à grande échelle ainsi que dans le contexte spécifique des forêts exploitées; 2) la contribution des éléphants de forêt à la régénération des espèces de bois de d'œuvre; et 3) les dommages causés par les éléphants de forêt aux espèces de bois d'œuvre. Bien que les activités humaines soient le facteur le plus important dans la répartition géographique des éléphants de forêt, c'est la disponibilité en nourriture, en eau et en minéraux qui conditionne localement leur utilisation de l'habitat. Dans certaines conditions, les concessions forestières peuvent abriter de grandes populations d'éléphants de forêt. En tant qu'important disperseur de graines, les éléphants de forêt contribuent à la régénération d'au moins 41 espèces de bois d'œuvre, telles que Bobgunnia fistuloides (pao rosa), l'un des bois les plus chers du marché. Les dommages causés par les éléphants de forêt sont divers et touchent un large éventail d'espèces. Du cassage des branches à l'écorçage des arbres, au moins 61 espèces de bois d'œuvre sont concernées, et peu de choses sont connues quant aux conséquences sur la vitalité de l'arbre et la qualité du bois. Les interactions entre les éléphants de forêt et l'exploitation forestière sont complexes et font intervenir de nombreuses variables, ce qui nécessite des recherches supplémentaires. Néanmoins, cette revue de la littérature suggère que les concessions forestières constituent des zones clés pour la conservation des éléphants de forêt, à condition qu'une exploitation à faible impact et une gestion de la faune soient mises en œuvre. Forest elephant populations have been seriously declining for decades. Covering 27% of the central African rainforest, timber concessions are key areas for the conservation of this emblematic species. Through an extensive literature review, we described the interactions between logging and forest elephants. Under specific conditions, timber concessions can host large populations of forest elephants, which contribute to the regeneration of many timber species. Conversely, foraging activities by forest elephants may also cause severe damage to trees, but the consequences to the tree's vitality and wood quality are unknown. We suggested additional research to identify the most appropriate management strategies and promote forest elephant conservation within timber concessions.
Article
Full-text available
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?.
Book
Full-text available
An Africa-wide overview of the distribution, abundance and conservation issues of African elephants as at the end of 2006. The introductory section is comprised of a short review outlining the background of the African Elephant Database, a discussion on the types of data and how is is it interpreted in the compilation of the report, and a descriptive text focused on the organization of the report. The body of the report initially presents the data at the continental level, following this data from the regions of Central Eastern, Southern and West Africa are presented with range states within each region reviewed in alphabetical order. Elephant population estimates and distributions from 37 range states in sub-Saharan Africa is consistently reviewed in concise text, clear tabular statistics and attractive population distribution maps. A comprehensive bibliography directly associated with the mapped information and three appendices, a quality index on the data, a comparative listing of estimates from regions and some protected areas in Eastern and Southern African countries, and an alphabetical listing of protected areas which fall within the elephant range throught the continent,complete the report.
Article
Full-text available
Protected from hunting and provided with access to water-holes during droughts, elephant numbers can double in a decade, severely damaging natural vegetation and the many species dependent upon it. Culling is an effective but controversial control strategy, so Fayrer-Hosken et al. have assessed the efficacy of using immunocontraception through vaccination, concluding that this could be a practical way of controlling elephant numbers. However, an intervention feasible in reproductive physiology may not be a practical way to control a population. Fayrer-Hosken et al. have not considered calculations that undermine the practicality of their method, nor alternative management strategies.
Article
Full-text available
Adult females were generally encountered accompanied by one or more offspring, and adult males were generally solitary. Mean group size was 2.8 individuals; mean size of a "Family Unit' was 3.5 individuals. Diet was diverse, including a minimum of 307 items. The bulk of the diet, in terms of number of species and quantities eaten, came from leaves and bark (70% of all items recorded). Trees represented 73% of the species fed upon. In contrast to savanna-living populations, fruit was an important part of the diet. Fruit of at least 72 species is eaten and the remains of at least one species of fruit was found in 82% of 311 fresh dung piles. -from Authors
Article
Full-text available
Ecosystem engineers are organisms that directly or indirectly modulate the availability of resources to other species, by causing physical state changes in biotic or abiotic materials. In so doing they modify, maintain and create habitats. Autogenic engineers (e.g. corals, or trees) change the environment via their own physical structures (i.e. their living and dead tissues). Allogenic engineers (e.g. woodpeckers, beavers) change the environment by transforming living or non-living materials from one physical state to another, via mechanical or other means. The direct provision of resources to other species, in the form of living or dead tissues is not engineering. Organisms act as engineers when they modulate the supply of a resource or resources other than themselves. We recognise and define five types of engineering and provide examples. Humans are allogenic engineers par excellence, and also mimic the behaviour of autogenic engineers, for example by constructing glasshouses. We explore related concepts including the notions of extended phenotypes and keystone species. Some (but not all) products of ecosystem engineering are extended phenotypes. Many (perhaps most) impacts of keystone species include not only trophic effects, but also engineers and engineering. Engineers differ in their impacts. The biggest effects are attributable to species with large per capita impacts, living at high densities, over large areas for a long time, giving rise to structures that persist for millennia and that modulate many resource flows (e.g. mima mounds created by fossorial rodents). The ephemeral nests constructed by small, passerine birds lie at the opposite end of this continuum. We provide a tentative research agenda for an exploration of the phenomenon of organisms as ecosystem engineers, and suggest that all habitats on earth support, and are influenced by, ecosystem engineers.
Article
Full-text available
Animals can play important roles in structuring the plant communities in which they live. Some species are particularly influential in that they modify the physical environment by changing, maintaining, and/or creating new habitats; the term ecosystem engineer has been used to describe such species. We here assess the two major foraging strategies of primates, frugivory and folivory, in terms of the potential for primates to function as ecosystem engineers. We argue that whereas the role of primates as seed dispersers has received a great deal of attention, the potential role that folivorous primates play in structuring their environment through herbivory has received much less attention. Further, while quantifying if frugivorous primates are ecosystem engineers through their seed dispersal has proved very difficult, it is not as difficult to ascertain whether folivorous primates are ecosystem engineers. We document situations in which folivorous primates act as ecosystem engineers by 1) eating the leaves and/or bark of trees to the extent that they kill trees, 2) feeding on trees to the degree that they slow their growth relative to nonpreferred tree species, 3) eating the flowers of species to the extent that it does not set fruit, or 4) feeding on plants in such a way as to increase their productivity and abundance. Because evidence from the literature is very limited, where possible we present new evidence of these processes from the colobus monkeys at our long-term field site in Kibale National Park, Uganda. We conclude by discussing promising research programs that could be established to refine our understanding of the role primates play in shaping the structure of plant communities, especially tropical forests.
Article
Full-text available
Conservation policy typically excludes people from national parks and manages encroachment by law enforcement. However, local people continue to extract resources from protected areas by boundary encroachment and poaching. This paper quantifies the patterns of illegal resource extraction from Kibale National Park in Uganda, the demand for Park resources by communities bordering the Park, and examines whether designated resource access agreements reduce illegal extraction. Sections of the Park boundary were examined and human entry trails, wood extraction, livestock grazing, and animal poaching signs were quantified. Levels of illegal extraction were compared with the demand for and admitted illegal access to resources inside the Park, collected in a survey of households located near the Park. Extraction was also compared between villages with and without negotiated resources access agreements. The most wanted and extracted resource from the Park was wood for fuel and construction. Implementation of resource access agreements with local community associations was found to be an effective means of reducing illegal extraction, but only if the association members profited from the agreement.
Article
Full-text available
African forest elephants- taxonomically and functionally unique-are being poached at accelerating rates, but we lack range-wide information on the repercussions. Analysis of the largest survey dataset ever assembled for forest elephants (80 foot-surveys; covering 13,000 km; 91,600 person-days of fieldwork) revealed that population size declined by ca. 62% between 2002-2011, and the taxon lost 30% of its geographical range. The population is now less than 10% of its potential size, occupying less than 25% of its potential range. High human population density, hunting intensity, absence of law enforcement, poor governance, and proximity to expanding infrastructure are the strongest predictors of decline. To save the remaining African forest elephants, illegal poaching for ivory and encroachment into core elephant habitat must be stopped. In addition, the international demand for ivory, which fuels illegal trade, must be dramatically reduced.
Article
Full-text available
The relationship between elephant damage and leaf nutrient concentration across tree species was investigated in a semi-arid savanna in western Zimbabwe with the purpose of investigating possible nutritional factors influencing elephant feeding preferences in Kalahari sand woodlands. The presence of elephant damage was recorded in all trees above 1 m in height, and leaf samples were collected from all tree species encountered in 12 vegetation plots during the late dry season. Elephant damage was positively correlated with leaf calcium, magnesium, potassium and protein concentration, but not with sodium, phosphorus or fibre. Tree species associated with sandy soils appeared to be less preferred by elephants and to have lower nutrient concentrations than species occurring on more fertile soils, such as species associated with termite mounds. Elephant damage may suppress recruitment in preferred tree species in these woodlands. This notion was supported by (1) the fact that 44% of all trees surveyed had had their main stems broken by elephants, a situation that leads to a multi-stemmed growth form with limited vertical growth; and (2) the negative correlation between the height of damaged trees and elephant damage across species.
Article
Full-text available
Elephant are believed to be one of the main ecological drivers in the conversion of savanna woodlands to grassland. We assessed the impacts of elephant on large trees (≥5 m in height) in the southern section of the Kruger National Park. Tree dimensions and utilization by elephant were recorded for 3082 individual trees across 22 transects (average length of 3 km and 10 m wide). Sixty per cent of the trees exhibited elephant utilization and 4% were dead as a direct result of elephant foraging behaviour. Each height class of tree was utilized in proportion to abundance. However, the size of the tree and the species influenced the intensity of utilization and foraging approach. Sclerocarya birrea was actively selected for and experienced the highest proportional utilization (75% of all trees). Interestingly, the proportion of large trees that were utilized and pushed over increased with distance from permanent water, a result which has implications for the provision of water in the KNP. We conclude that mortality is likely to be driven by a combination of factors including fire, drought and disease, rather than the actions of elephant alone. Further investigation is also required regarding the role of senescence and episodic mortality.
Article
Full-text available
This study investigated the nutritional ecology of forest elephants in Kibale National Park, Uganda relative to crop-raiding behaviour, and examined nutritional differences between crops and food consumed by wild elephants. An index of dietary nutrient concentration was determined by quantifying the species and parts of plants consumed along feeding trails, collecting food items, and analysing foods for energy, fibre, protein, minerals and secondary compounds. Frequency of crop raiding was quantified over 13 mo. Energy and protein concentration was within suggested levels, but concentrations of several minerals, particularly sodium, were low relative to requirements based on captive elephants and values reported for other wild populations. The very low sodium concentrations of Kibale elephant diets and low availability of alternative sodium sources, such as soil or water, suggest that sodium drive is very likely in this population. Crops consumed by Kibale elephants had higher Na concentrations and lower concentrations of fibre and secondary compounds than wild diets. The known attraction of elephants to mineral sources throughout their range and the low mineral concentration of leaves, fruits, bark, and stems consumed by forest elephant in this study suggest that mineral nutrition is likely to be an important factor driving elephant behaviour and patterns of habitat use.
Article
Full-text available
This study demonstrates that forest elephants (Loxodonta africana) play a key role as seed dispersal agents for the upper canopy forest tree, Balanites wilsoniana. Seed that passed through elephants had a much greater probability of germinating (50.7%) than seeds from fruits eollected directly from the tree (3%). Of 515 seeds that were collected from under parent trees, 89.1% were rotten at the time of collection, 2.6% had been eaten by forest pigs, 2.8% had been killed by squirrels, and 0.7% had been killed by insect damage. The remaining 4.8% of the seeds were still alive. In 150 hours of focal observations on B. wilsoniana trees, two fruits were seen to be destroyed by squirrels, no fruits were seen to be consumed by potential dispersers, and no evidence of scatter hoarding was found. Experimental seedling stations placed out under parent trees and away from parent trees indicated no significant effect of dispersal on seedling survival. Although elephants are not essential for the successful germination of B. wilsoniana seeds, they do greatly increase probability of germination and play a vital role in their dispersal, suggesting that this is a highly interdependent plant-animal seed dispersal system.
Article
Full-text available
The extensive area of degraded tropical land and the calls to conserve forest biodiversity and sequester carbon to offset climate change demonstrate the need to restore forest in the tropics. Deforested land is sometimes replanted with fast-growing trees; however, the consequences of intensive replanting on biomass accumulation or plant and animal diversity are poorly understood. The purpose of this study was to determine how intensive replanting affected tropical forest regeneration and biomass accumulation over ten years. We studied reforested sites in Kibale National Park, Uganda, that were degraded in the 1970s and replanted with five native tree species in 1995. We identified and measured the size of planted versus naturally regenerating trees, and felled and weighed matched trees outside the park to calculate region-specific allometric equations for above-ground tree biomass. The role of shrubs and grasses in facilitating or hindering the establishment of trees was evaluated by correlating observed estimates of percent cover to tree biomass. We found 39 tree species naturally regenerating in the restored area in addition to the five originally planted species. Biomass was much higher for planted (15,675 kg/ha) than naturally regenerated trees (4560 kg/ha), but naturally regenerating tree regrowth was an important element of the landscape. The establishment of tree seedlings initially appeared to be facilitated by shrubs, primarily Acanthus pubescens and the invasive Lantana camara; however, both are expected to hinder tree recruitment in the long-term. Large and small-seeded tree species were found in the replanted area, indicating that bird and mammal dispersers contributed to natural forest restoration. These results demonstrate that intensive replanting can accelerate the natural accumulation of biomass and biodiversity and facilitate the restoration of tropical forest communities. However, the long-term financial costs and ecological benefits of planting and maintaining reforested areas need to be weighed against other potential restoration strategies.Research highlights▶ Intensive tree planting produced a closed canopy regenerating forest with10 years. ▶ 39 naturally regenerating tree species were found in the replanted forest. ▶ Shrubs, particularly Lantana camara, threaten the future success of the regeneration.
Book
The author summarizes 20 years of research in the Kibale forest in Uganda. The main body of the book demonstrates the adverse effects of logging on community structure and other aspects of forest ecology. The author provides evidence that future logging must be done at far lower intensities than is currently the norm, if intact ecosystems are to be maintained. Detailed recommendations for harvest plans compatible with the conservation of biodiversity and ecological integrity are outlined. Struhsaker addresses the underlying causes of tropical deforestation and concludes that although there are numerous proximate factors, the ultimate causes are rapidly increasing human populations and rates of consumption per capita. Comparisons with relevant studies elsewhere in the tropics are drawn and specific recommendations to address the problems are offered.
Article
Interactions between organisms are a major determinant of the distribution and abundance of species. Ecology textbooks (e.g., Ricklefs 1984, Krebs 1985, Begon et al. 1990) summarise these important interactions as intra- and interspecific competition for abiotic and biotic resources, predation, parasitism and mutualism. Conspicuously lacking from the list of key processes in most text books is the role that many organisms play in the creation, modification and maintenance of habitats. These activities do not involve direct trophic interactions between species, but they are nevertheless important and common. The ecological literature is rich in examples of habitat modification by organisms, some of which have been extensively studied (e.g. Thayer 1979, Naiman et al. 1988).
Article
Light gap disturbances have been postulated to play a major role in maintaining tree diversity in species-rich tropical forests. This hypothesis was tested in more than 1200 gaps in a tropical forest in Panama over a 13-year period. Gaps increased seedling establishment and sapling densities, but this effect was nonspecific and broad-spectrum, and species richness per stem was identical in gaps and in nongap control sites. Spatial and temporal variation in the gap disturbance regime did not explain variation in species richness. The species composition of gaps was unpredictable even for pioneer tree species. Strong recruitment limitation appears to decouple the gap disturbance regime from control of tree diversity in this tropical forest.
Article
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.
Article
Four aerial counts of elephants (Loxodonta africana) on a 1,500-square-mile area, including the southern two-thirds of Murchison Falls National Park and vicinity, Uganda, were made from July, 1963, to May, 1964. The average number of 6,750 elephants was about 1,000 below the average counted in the same area in 1958-59. An unusually long dry season between mid-June and early November, 1963, caused an early movement of elephants from the grasslands of the study area to the woodlands outside. With the onset of rains in late November, elephants began moving back to the study area. They continued this movement into the December-March Dry Season, concentrating near streams and in unburned woodlands of green vegetation. During the March-May Rainy Season major migrations occurred. The highest count was enumerated at this time and elephants were widely distributed. On two adjacent areas to the north (Tangi-Karuma area and the Elephant Sanctuary) three aerial counts indicated similar distributions and seasonal movements. However, data from four aerial counts in 767-square-mile Queen Elizabeth National Park in southwestern Uganda showed different seasonal distributions and movements: 1,758 elephants in the June-August Dry Season, 1,329 in the August-November Rainy Season, a further decline to 1,295 in the December-March Dry Season, and an increase to 2,222 in the March-May Rainy Season. Annual increment varied inversely with population density. The highest increment (8-9 percent) was in Q. E. Park where the average density was 2.2 elephants/square mile and restrictions on migrations are minor. The next highest annual increment (7-7.5 percent) was on the combined Tangi-Karuma area and the Elephant Sanctuary, north of the 1,500-square-mile study area. Here the average density was 2.8 elephants/square mile and migrations have not been appreciably restricted. The lowest annual increment (6-6.5 percent) was obtained on the 1,500-mile study area where density averaged 4.5 elephants/square mile. It is here that drastic changes have occurred to distribution of elephants, and serious restrictions have been imposed on their migratory behavior.
Article
: 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.
Article
The African elephant is the largest extant terrestrial mammal and a reminder of the Pleistocene megafauna. Their survival is, however, dependent on conservation areas. In some conservation areas, rapidly growing elephant populations have led conservation biologists to ask, how many elephants can these areas support? The debate is polarized by arguments for large populations for economic, social, or ethical reasons and arguments for smaller populations that avoid biodiversity loss. We use a novel dynamic modeling approach to assess how climate change-induced vegetation change may influence the capacity of a conservation area to support large herbivores. The model projects that elephant densities and fire have substantial impacts on vegetation under current climatic conditions. Under future conditions, the capacity to support elephants increases due to CO2-induced increases in woody plant productivity. We conclude that sustainable management in conservation areas needs to be conditioned on the effects of climate change on vegetation.
Article
The metabolic rate—body size relationship suggests that the African elephant (Loxodonta africana) should be least selective among mammalian herbivores in its diet. However, selection among plant species needs to be distinguished from selection for plant parts or other features. We investigated seasonal variation in the selective utilization and dietary contribution of woody plant species, parts, and height classes to vegetation consumed by elephants in the Kalahari sandveld region of Chobe National Park, Botswana. Only 30% of 27 common woody species were moderately or highly acceptable to elephants in the wet season, increasing to more than 50% in the hot dry season. Six woody species remained mostly or entirely rejected by elephants throughout the year. Most of the browse consumed during each season came from 1 or 2 common shrub species. Leaves and leaf-bearing shoots constituted 80% of the material consumed from woody plants during the wet season, but only 45% during the cool dry season. Stem, bark, and root tissues contributed 50% of the woody plant component of the diet in the cool dry season, increasing to 94% in the hot dry season. Hence, despite their narrow selection for plant species, large size coupled with hindgut digestion enables elephants to exploit a wide range of plant parts, including fibrous stems, bark, and roots. Accordingly, elephants occupy a dietary niche distinct from browsing or grazing ruminants.
Article
Uncertainty in recovery times of tropical forests can lead to mismanagement, such as in setting inappropriate harvesting rates or failing to achieving conservation targets. We use long-term plot data (17y) to estimate recovery times of separate forest compartments, which experienced different levels of timber extraction within Kibale National Park, Uganda. We estimate that structural recovery (basal area) of heavily logged and moderately logged compartments will take respectively 112 and 95y, when compared to adjacent mature forest. Our data suggests that recovery in terms of species composition will take significantly longer. Our estimates of structural recovery are derived from rates of change of diameter at breast height and basal area measurements which have been used traditionally as indicators of forest growth and productivity. Our results suggest that the severity of the logging has an impact on the rate of recovery, with current recovery rates estimated at 0.32m2ha−1y−1 in a moderately logged compartment and 0.25m2ha−1y−1 in heavily logged areas, highlighting the possible benefits of reduced impact harvesting in increasing long-term yields. We investigate how some representatives of the wildlife community were affected by differential recovery times and find that recovery times of frugivorous primate's forest habitats were 2.5 times slower when compared with folivorous primates.
Article
The assessment of food abundance is critical to address many theoretical questions concerning chimpanzee ecology and social organization. A variety of methods have been used to estimate habitat-wide food abundance. Since methods vary between sites, it is difficult to make meaningful intersite comparisons, without calibration of the different methods. We compare three methods used to estimate fruit abundance simultaneously in the Kibale Forest Reserve, Uganda. Estimates of fruit abundance derived from fruit traps were not related to estimates derived from either systematic transect sampling or estimates obtained from observing fruiting phenology of key species on a fruit trail. However, estimates based on fruit trail data and transect data were correlated. We also report the results of surveys for herbaceous food availability using data from three different sites, employing similar, but not identical methods. The results of these analyses illustrate the difficulties encountered when data generated by divergent methods are compared, and we present specific recommendations as to how future studies might be structured to facilitate comparability between sites.
Article
The floristic and structural changes in the vegetation resulting from the long-term exclusion of large herbivores from experimental plots in the Murchison Falls National Park, Uganda, are described.Two experimental plots were surveyed, one in Sporobolus-Setaria grassland and the other in Combretum-Terminalia woodland. The survey shows that long-term removal of grazing and browsing pressure results in (1) marked tree regeneration in both grassland and woodland plots; (2) a relatively species-poor herbaceous layer in the grassland plot; and (3) the development of a more diverse all-aged stand in the woodland plot. These results are discussed in the context of the poaching of large herbivores during the 1978 civil war and the concomitant vegetation changes, especially Acacia sieberiana regeneration, that are now occurring throughout the Park. The implications for future management of the Park are discussed.
Article
Evidence from southern African semi-arid savannas suggests that high elephant densities in nature reserves cause the over-utilization of woodlands. Northern Botswana, with its prolific elephant population, is expected to follow such a pattern unless the densities of elephants which could be sustained by indigenous woodlands are determined and maintained at carrying capacity. Above ground biomass production was estimated for mopane (Colophospermum mopane) woodlands, a principal food source for elephants, which grows over much of northern Botswana. Densities of trees and shrubs, dimensions of plants and elephant densities were recorded within stratified plots situated according to a regional rainfall gradient. Mean estimates of above ground biomass (foliage and twigs) were 9.41 and 7.83 t ha−1 for shrubs and trees respectively. A logistic model described the maximum levels of biomass removal from plants before over-utilization of mopane occurred. Variables incorporated in the model included above ground biomass of mopane shrubs and trees, growth rates of plants and expected off-take by elephants. The model predicted a complete biomass regain within 10 y if no elephant browsing occurs. Intensive elephant browsing in woodlands containing 15 elephants km−2, however, can suppress biomass production if growth rates of plants fall below 70% of the maximum annual rate. Nonetheless, there was no substantial evidence to suggest that elephants will reduce the biomass of mopane woodlands in northern Botswana below a sustainable level if their numbers are allowed to increase considerably beyond the current estimate.
Article
The Kibale Forest, western Uganda, is the only site where studies have compared the impact of elephants on rainforest regeneration in logged and unlogged control areas. Elephants used heavily logged areas more than lightly logged and unlogged areas. Forest gaps were used more by elephants than closed-canopy areas and large gaps more than small ones. Gaps were larger in logged than unlogged forest. There were lower densities of young trees (saplings and poles) and a higher incidence of elephant damage to them in heavily logged forest than in lightly logged and unlogged sites. Elephant use of an area and damage to young trees was inversely or unrelated to the density of young trees and directly related to the density of herbaceous tangle. Heavy logging resulted in large areas of herbaceous tangle, which attracted elephants who suppressed forest regeneration by damaging young trees and perpetuating the herbaceous tangle. The tangle directly competed with regeneration of young trees while also attracting elephants and rodents (seed and seedling predators) and facilitating increased windthrow of trees. Selective browsing of young trees by elephants affected rates of regeneration, growth form and species composition. Rather than remove elephants, a more effective and humane approach to long-term management of logging is to reduce logging offtake and incidental damage caused by timber extraction.
Article
During Uganda's political troubles in the 1970s the country's few remaining natural forests suffered acutely from illegal human encroachment, poor management practices and poaching of endangered forest wildlife. While the Kibale Forest suffered from many problems, agricultural encroachment alone destroyed some 97 sq km, or 17 per cent, of the Reserve between 1971 and 1982. In 1983 the Government of Uganda initiated steps to halt the spread of encroachment and to reassert authority over its forest resources.
Article
1. Primates dominate lists of pests that damage crops around African parks and reserves. Beyond creating management problems, crop foraging is integral to the ecology of primates inhabiting forest-agriculture ecotones. 2. Twenty-three months of data from four villages around Kibale National Park, Uganda, revealed that redtail monkeys Cercopithecus ascanius, olive baboons Papio cynocephalus and chimpanzees Pan troglodytes selected different crops or plant parts. Baboons took root and tuber crops ignored by other primates, and fed on the greatest variety of crops. All three species preferred maize and/or bananas. Redtails ate only banana fruit, baboons ate banana fruit more frequently than pith, and chimpanzees raided pith and fruit in equal proportions. 3. Each primate showed a distinct monthly pattern of crop foraging, significantly non-random for baboons and redtail monkeys, weakly for chimpanzees. Large intermonthly variation was observed for all three primates, but was least pronounced in redtails. 4. Raiding frequency on maize peaked approximately 8 weeks after the onset of rains and was strongly correlated between the three primate species. Abundant forest fruit did not diminish primate appetite for maize. 5. Raiding frequency on bananas varied considerably despite continuous availability of fruit and pith. Peaks in banana consumption were unrelated to rainfall or maize raiding, but were associated instead with forest fruit shortages, specifically Mimusops bagshawei. 6. Chimpanzees consumed banana pith more frequently when forest fruits were scarce, whereas baboons targeted more banana fruits. The use of banana pith by chimpanzees supports the suggestion that energy-rich pith is crucial to chimpanzees during fruit scarcity. 7. Conservation of Mimusops bagshawei and other key forest fruit trees may lessen primate raiding intensity on perennial crops, e.g. bananas. Maize raiding appears unaffected by forest fruit abundance. Such highly palatable crops are best planted > 500 m from the forest edge. 8. Planting agroforestry buffers along park edges creates ideal habitat for crop-raiders. This management strategy is appropriate where human population density is low and crop raiding species are legal game. When dangerous or destructive wildlife species forage amidst densely settled subsistence farmland, managers are challenged to separate forests from agriculture using non-palatable plant barriers or electric fences.
Article
The present work was initiated to determine the status of the elephant in Uganda following reports of overpopulation in the national parks. Aerial counts were carried out each September from 1973 to 1976 in Rwenzori National Park and in Kabalega Falls National Park, including the contiguous game reserves to the south. The results showed a significant decline in elephant numbers between 1973 and 1976. By 1976 the populations in Rwenzori and Kabalega had fallen to about 26% and 17% respectively of the 1973 level. The decline is attributed to a massive increase in poaching within the parks. These findings necessitate a completely new assessment of the elephant problem in Uganda and published recommendations to cull are obviously no longer relevant. La présente étude a été entreprise pour déterminer la situation de I'éléphant en Ouganda en fonction des rapports de surpopulation dans les parcs nationaux. Des mois de septembre entre 1973 et 1976 au Parc National du Rwenzori et au Parc National de Kabalega Falls, y compris les réserves de chasse contigües au sud. Les résultats montrent une diminution significative du nombre d'éléphants entre ces deux années. En 1976, les populations au Rwenzori et au Kabalega sont tombées respectivement à 26 et 17% des effectifs de 1973. Le déclin est attribuéà une augmentation massive du braconnage à l'intérieur des parcs. Ces découvertes nécessitent une approche entiérement nouvelle du problème des éléphants en Ouganda et les publications antérieures recommandant un prélèvement ne sont manifestement plus appropriées.
Book
Prologue 1. Morphology, evolutionary history and recent distribution 2. Food and other habitat resources 3. Space-time patterns of habitat use 4. Body size and nutritional physiology 5. Body size and feeding ecology 6. Social organisation and behaviour 7. Life history 8. Body size and sociobiology 9. Body size and reproductive patterns 10. Demography 11. Community interactions 12. Body size and population regulation 13. Body size and ecosystem processes 14. Late Pleistocene extinctions 15. Conservation Epilogue: the megaherbivore syndrome Appendixes References Index.
Article
The types of social organisation displayed by the African antelope species have been assigned in this paper to five classes, distinguished largely by the strategies used by the reproductively active males in securing mating rights, and the effects of those strategies on other social castes. The paper attempts to show that these strategies are appropriate to each class because of the effects of other, ecological, aspects of their ways of life. The paper describes different feeding styles among antelope, in terms of selection of food items and coverage of home ranges. It argues that these feeding styles bear a relationship to maximum group size of feeding animals through the influence of dispersion of food items upon group cohesion. The feeding styles also bear a relationship to body size and to habitat choice, both of which influence the antelope species' antipredator behaviour. Thus feeding style is related to anti-predator behaviour which, in many species, influences minimum group size. Group size and the pattern of movement over the annual home range affect the likelihood of females being found in a given place at a given time, and it is this likelihood which, to a large extent, determines the kind of strategy a male must employ to achieve mating rights. The effects of the different strategies employed by males can be seen in such aspects of each species' biology as sexual dimorphism, adult sex ratio, and differential distribution of the sexes.