Mike Peel - Academia.edu (original) (raw)

Papers by Mike Peel

PLOS ONE, 2019

How do large-mammal communities reassemble after being pushed to the brink of extinction? Few dat... more How do large-mammal communities reassemble after being pushed to the brink of extinction? Few data are available to answer this question, as it is rarely possible to document both the decline and recovery of wildlife populations. Here we present the first in-depth quantitative account of war-induced collapse and postwar recovery in a diverse assemblage of large herbivores. In Mozambique's Gorongosa National Park, we assembled data from 15 aerial wildlife counts conducted before (1968-1972) and after (1994-2018) the Mozambican Civil War (1977-1992). Prewar total biomass density exceeded 9,000 kg km-2 , but populations declined by >90% during the war. Since 1994, total biomass has substantially recovered, but species composition has shifted dramatically. Formerly dominant large herbivores-including elephant (Loxodonta africana), hippo (Hippopotamus amphibius), buffalo (Syncerus caffer), zebra (Equus quagga), and wildebeest (Connochaetes taurinus)-are now outnumbered by waterbuck (Kobus ellipsiprymnus) and other small to mid-sized antelopes. Waterbuck abundance has increased by an order of magnitude, with >55,000 individuals accounting for >74% of large-herbivore biomass in 2018. By contrast, elephant, hippo, and buffalo, which totaled 89% of prewar biomass, now comprise just 23%. These trends mostly reflect natural population growth following the resumption of protection under the Gorongosa Restoration Project; reintroductions (465 animals of 7 species) accounted for a comparatively small fraction of the total numerical increase. Waterbuck are growing logistically, apparently as-yet unchecked by interspecific competition or predation (apex-carnivore abundance has been low throughout the postwar interval), suggesting a community still in flux. Most other herbivore populations have increased postwar , albeit at differing rates. Armed conflict remains a poorly understood driver of ecological change; our results demonstrate the potential for rapid postwar recovery of large-herbivore biomass, given sound protected-area management, but also suggest that restoration of community structure takes longer and may require active intervention.

Forest Ecology and Management, 2006

Identification of the factors that determine the variation in browse quality, as determined by th... more Identification of the factors that determine the variation in browse quality, as determined by their chemical composition, is an important step towards understanding herbivore distribution patterns. Therefore, the variation in leaf chemical composition (digestibility lowering compounds: condensed tannin and total polyphenol concentration, and nutrients: nitrogen and phosphorous concentration) was related to geomorphology, vegetation structure, and fire history, in mopane (Colophospermum mopane) open woodland in Kruger National Park. The results show that the principle drivers of foliar nitrogen, condensed tannins and total polyphenols differ from those for foliar phosphorus. Nitrogen, condensed tannin and total polyphenol concentrations are mainly determined by the effect of fire. The foliar concentration of phosphorus is mainly determined by parent material. This difference may be related to differences in the mobility of nitrogen and phosphorous in the soil.

A&A, 2014

We discuss the methods employed to photometrically calibrate the data acquired by the Low Frequen... more We discuss the methods employed to photometrically calibrate the data acquired by the Low Frequency Instrument on Planck. Our calibration is based on a combination of the orbital dipole plus the solar dipole, caused respectively by the motion of the Planck spacecraft with respect to the Sun and by motion of the solar system with respect to the cosmic microwave background (CMB) rest frame. The latter provides a signal of a few mK with the same spectrum as the CMB anisotropies and is visible throughout the mission. In this data release we rely on the characterization of the solar dipole as measured by WMAP. We also present preliminary results (at 44 GHz only) on the study of the Orbital Dipole, which agree with the WMAP value of the solar system speed within our uncertainties. We compute the calibration constant for each radiometer roughly once per hour, in order to keep track of changes in the detectors' gain. Since non-idealities in the optical response of the beams proved to be important, we implemented a fast convolution algorithm which considers the full beam response in estimating the signal generated by the dipole. Moreover, in order to further reduce the impact of residual systematics due to sidelobes, we estimated time variations in the calibration constant of the 30 GHz radiometers (the ones with the largest sidelobes) using the signal of an internal reference load at 4 K instead of the CMB dipole. We have estimated the accuracy of the LFI calibration following two strategies: (1) we have run a set of simulations to assess the impact of statistical errors and systematic effects in the instrument and in the calibration procedure; and (2) we have performed a number of internal consistency checks on the data and on the brightness temperature of Jupiter. Errors in the calibration of this Planck/LFI data release are expected to be about 0.6% at 44 and 70 GHz, and 0.8% at 30 GHz. Both these preliminary results at low and high are consistent with WMAP results within uncertainties and comparison of power spectra indicates good consistency in the absolute calibration with HFI (0.3%) and a 1.4σ discrepancy with WMAP (0.9%).

African Journal of Range & Forage Science, 2018

Holistic Planned Grazing™ (HPG) is purported to have positive long-term effects on rangelands, en... more Holistic Planned Grazing™ (HPG) is purported to have positive long-term effects on rangelands, enhancing ecosystem services. Given comparable environmental templates, but different management regimes, vegetation monitoring and landscape function analysis showed the Africa Center for Holistic Management (ACHM) at Dimbangombe had a significantly higher rangeland condition (composition, cover, standing crop and soil health) than adjacent Sizinda (SCR) and Monde (MCR) communal rangelands. Overall grazer density on ACHM is 42% higher than that of SCR (no data for MCR). Finer-scale satellite collar data for ACHM yielded a calculated stocking rate of 0,55 LSU ha-1 y-1 or 24 590 kg km-2, which constitutes high-density grazing. An energy flow estimate shows that the grazing resource would, on average, not be limiting for livestock on ACHM but limiting on SCR. HPG may include an element where kraals are inserted into degraded rangelands for a short period. Overall, ACHM shows stable perennial composition with smaller tufts significantly closer together. A similar result was visible in SCR where maize yields were visibly higher on kraaled areas than on adjacent untreated fields. HPG yields positive long-term effects on ecosystem services (soils and vegetation) and points to the HPG approach enhancing the sustainability of livestock and wildlife in this environment.

IIRS courses Dean of IIRS 13 ENVISAT launched Boudewijn van Leeuwen 15

PLOS ONE, May 16, 2018

Savanna ecosystems are popular subjects for interaction studies. Multiple studies have been done ... more Savanna ecosystems are popular subjects for interaction studies. Multiple studies have been done on the impact of elephants on vegetation, the impact of grass and browse availability on animal densities or on competition between herbivore species. Previous studies showed that elephant densities are frequently negatively correlated with densities of tall trees, and that browse and grass availability are correlated with browser and grazer density respectively. Additionally, a competition effect between browse and grass availability has been reported. These relationships are usually analysed by testing direct relationships between e.g., herbivore densities and food availability, without addressing competition effects or other indirect effects. In this study, multiple interactions in a savanna system have been analysed simultaneously using Partial Least Square-Path Modelling (PLS-PM) using mammal and vegetation data from three different wildlife reserves in southern KwaZulu-Natal. The results showed that the processes that three separate models for the three areas provided the best understanding of the importance of the different interactions. These models suggest that elephants had a negative impact on trees, but also on grass availability. The impact is stronger when elephants are not able to migrate during the dry season. Browsers and grazers were correlated with browse and grass availability, but competition between browse and grass was not detected. This study shows that due to the complexity of the interactions in an ecosystem and differences in environmental factors, these interactions are best studied per area. PLS-PM can be a useful tool for estimating direct, indirect, and cascading effects of changing animal densities in conservation areas.

Nature Ecology & Evolution, 2020

Journal of Applied Ecology, 2016

Functional heterogeneity refers to spatial and temporal variation in the grass height (structure)... more Functional heterogeneity refers to spatial and temporal variation in the grass height (structure), productivity, phenology, composition and chemical attributes of grassland

African Journal of Range & Forage Science

Drought is a natural phenomenon that plays an important role in non-equilibrium disturbance drive... more Drought is a natural phenomenon that plays an important role in non-equilibrium disturbance driven ecosystems. As such, droughts are considered natural and therefore by definition ecologically desirable in many ecosystems (e.g. Frederick and Ogden 2001). However, droughts happen in a particular space-time context, and as such droughts often interact with management activities. These interactions may either reduce or exacerbate drought effects, even in large protected areas (e.g. Walker et al. 1987). It is therefore critical to understand the interplay between drought and management actions in order to inform decision making in protected areas in a future where droughts are expected to become more frequent and intense (Knapp et al. 2008; IPCC 2012). There are four key management actions, all of which influence quantity, quality and/or distribution of key resources, which may influence the effect of droughts on animals, especially in arid or semi-arid protected areas (i.e. MAP <750 mm annum −1): (i) addition or removal of surface water sources (i.e. artificial water provision), (ii) expansion or contraction of area available to herbivores (e.g. consolidation and/or expansion of protected areas and/or migratory corridors), (iii) population control or not (e.g. translocation, culling, contraception) of abundant and/or large-bodied species that have considerable forage requirements, and (iv) addition of forage resources (e.g. provision of supplementary feeding). The following subsections focus on the first three management actions listed above (the fourth management action is neither feasible nor desirable in large protected areas, and as such is not further discussed). Each subsection formulates an adaptive management hypothesis based on current understanding of how the specific management action interacts with drought. An adaptive management hypothesis is essentially a prediction of what is expected to happen (to megaherbivores during a drought in the case of this study) under the different management approaches. This study thereafter sets out to evaluate these hypotheses using spatially explicit long-term

South African Journal of Science

Nature is experiencing degradation and extinction rates never recorded before in the history of E... more Nature is experiencing degradation and extinction rates never recorded before in the history of Earth. 1,2 Consequently, continuous large-scale monitoring programmes are critical, not only to provide insights into population trends but also to aid in understanding factors associated with altering population dynamics at various temporal and spatial scales. 3 Continuous monitoring is important not only for tracking rare or threatened species but also to detect the increase of potentially invasive species 4 , and the trends in the populations of common species, which in some regions are declining even more rapidly than are rare species 2 .

African Journal of Range & Forage Science

African Journal of Range & Forage Science

Journal of the Grassland Society of Southern Africa

Herbaceous plant species composition was measured on ranches in the Thabazimbi district, Transvaa... more Herbaceous plant species composition was measured on ranches in the Thabazimbi district, Transvaal, to obtain veld composition scores and to quantify the relations between such scores and certain determinants considered important in influencing species composition. Determinants investigated were mean annual rainfall and herbivory (stocking rate). The survey was undertaken on seven game and cattle ranches in Combretum apiculatum woodland of

African Journal of Range & Forage Science

European Journal of Wildlife Research, 2015

Elephant Loxodonta africana conservation might indirectly influence the wider herbivore community... more Elephant Loxodonta africana conservation might indirectly influence the wider herbivore community structure, as elephants have the ability to significantly modify the savanna habitat. Uncertainty remains as to the consequences of these effects, as elephants might either compete with other species or facilitate foraging especially for grazers and smaller browsing species by increasing the amount of grass or the amount of browse at lower feeding heights. We studied these potential cascading effects of elephants by using 16 years of data (1992-2011) from the Sabi Sand Wildtuin, South Africa, which showed a steady increase in elephant densities from 0.12 to 2.03 elephants/km 2 over this period. We demonstrate that tree densities, and browse availability at feeding heights below 2 m, decreased with increasing elephant densities, and that there was no positive effect of elephants on browse availability. The changes in elephant densities were good predictors (R 2 adj >0.50) in explaining population fluctuations of other herbivore species. The total body mass of grazers increased more than that of the browsers, shifting the community toward a grazer and megaherbivore-dominated community. An increasing density of elephants changes the composition of the herbivore community, as mesobrowsers are unable to benefit from the impact of elephants on trees, but megagrazers show strong positive responses. Hence, changes in elephant densities as a result of poaching or conservation may trigger cascading community effects. These are neglected but important consequences of (negative or positive) human impacts on elephant numbers, especially in restricted areas such as reserves and national parks.

PLOS ONE, 2019

How do large-mammal communities reassemble after being pushed to the brink of extinction? Few dat... more How do large-mammal communities reassemble after being pushed to the brink of extinction? Few data are available to answer this question, as it is rarely possible to document both the decline and recovery of wildlife populations. Here we present the first in-depth quantitative account of war-induced collapse and postwar recovery in a diverse assemblage of large herbivores. In Mozambique's Gorongosa National Park, we assembled data from 15 aerial wildlife counts conducted before (1968-1972) and after (1994-2018) the Mozambican Civil War (1977-1992). Prewar total biomass density exceeded 9,000 kg km-2 , but populations declined by >90% during the war. Since 1994, total biomass has substantially recovered, but species composition has shifted dramatically. Formerly dominant large herbivores-including elephant (Loxodonta africana), hippo (Hippopotamus amphibius), buffalo (Syncerus caffer), zebra (Equus quagga), and wildebeest (Connochaetes taurinus)-are now outnumbered by waterbuck (Kobus ellipsiprymnus) and other small to mid-sized antelopes. Waterbuck abundance has increased by an order of magnitude, with >55,000 individuals accounting for >74% of large-herbivore biomass in 2018. By contrast, elephant, hippo, and buffalo, which totaled 89% of prewar biomass, now comprise just 23%. These trends mostly reflect natural population growth following the resumption of protection under the Gorongosa Restoration Project; reintroductions (465 animals of 7 species) accounted for a comparatively small fraction of the total numerical increase. Waterbuck are growing logistically, apparently as-yet unchecked by interspecific competition or predation (apex-carnivore abundance has been low throughout the postwar interval), suggesting a community still in flux. Most other herbivore populations have increased postwar , albeit at differing rates. Armed conflict remains a poorly understood driver of ecological change; our results demonstrate the potential for rapid postwar recovery of large-herbivore biomass, given sound protected-area management, but also suggest that restoration of community structure takes longer and may require active intervention.

Forest Ecology and Management, 2006

Identification of the factors that determine the variation in browse quality, as determined by th... more Identification of the factors that determine the variation in browse quality, as determined by their chemical composition, is an important step towards understanding herbivore distribution patterns. Therefore, the variation in leaf chemical composition (digestibility lowering compounds: condensed tannin and total polyphenol concentration, and nutrients: nitrogen and phosphorous concentration) was related to geomorphology, vegetation structure, and fire history, in mopane (Colophospermum mopane) open woodland in Kruger National Park. The results show that the principle drivers of foliar nitrogen, condensed tannins and total polyphenols differ from those for foliar phosphorus. Nitrogen, condensed tannin and total polyphenol concentrations are mainly determined by the effect of fire. The foliar concentration of phosphorus is mainly determined by parent material. This difference may be related to differences in the mobility of nitrogen and phosphorous in the soil.

A&A, 2014

We discuss the methods employed to photometrically calibrate the data acquired by the Low Frequen... more We discuss the methods employed to photometrically calibrate the data acquired by the Low Frequency Instrument on Planck. Our calibration is based on a combination of the orbital dipole plus the solar dipole, caused respectively by the motion of the Planck spacecraft with respect to the Sun and by motion of the solar system with respect to the cosmic microwave background (CMB) rest frame. The latter provides a signal of a few mK with the same spectrum as the CMB anisotropies and is visible throughout the mission. In this data release we rely on the characterization of the solar dipole as measured by WMAP. We also present preliminary results (at 44 GHz only) on the study of the Orbital Dipole, which agree with the WMAP value of the solar system speed within our uncertainties. We compute the calibration constant for each radiometer roughly once per hour, in order to keep track of changes in the detectors' gain. Since non-idealities in the optical response of the beams proved to be important, we implemented a fast convolution algorithm which considers the full beam response in estimating the signal generated by the dipole. Moreover, in order to further reduce the impact of residual systematics due to sidelobes, we estimated time variations in the calibration constant of the 30 GHz radiometers (the ones with the largest sidelobes) using the signal of an internal reference load at 4 K instead of the CMB dipole. We have estimated the accuracy of the LFI calibration following two strategies: (1) we have run a set of simulations to assess the impact of statistical errors and systematic effects in the instrument and in the calibration procedure; and (2) we have performed a number of internal consistency checks on the data and on the brightness temperature of Jupiter. Errors in the calibration of this Planck/LFI data release are expected to be about 0.6% at 44 and 70 GHz, and 0.8% at 30 GHz. Both these preliminary results at low and high are consistent with WMAP results within uncertainties and comparison of power spectra indicates good consistency in the absolute calibration with HFI (0.3%) and a 1.4σ discrepancy with WMAP (0.9%).

African Journal of Range & Forage Science, 2018

Holistic Planned Grazing™ (HPG) is purported to have positive long-term effects on rangelands, en... more Holistic Planned Grazing™ (HPG) is purported to have positive long-term effects on rangelands, enhancing ecosystem services. Given comparable environmental templates, but different management regimes, vegetation monitoring and landscape function analysis showed the Africa Center for Holistic Management (ACHM) at Dimbangombe had a significantly higher rangeland condition (composition, cover, standing crop and soil health) than adjacent Sizinda (SCR) and Monde (MCR) communal rangelands. Overall grazer density on ACHM is 42% higher than that of SCR (no data for MCR). Finer-scale satellite collar data for ACHM yielded a calculated stocking rate of 0,55 LSU ha-1 y-1 or 24 590 kg km-2, which constitutes high-density grazing. An energy flow estimate shows that the grazing resource would, on average, not be limiting for livestock on ACHM but limiting on SCR. HPG may include an element where kraals are inserted into degraded rangelands for a short period. Overall, ACHM shows stable perennial composition with smaller tufts significantly closer together. A similar result was visible in SCR where maize yields were visibly higher on kraaled areas than on adjacent untreated fields. HPG yields positive long-term effects on ecosystem services (soils and vegetation) and points to the HPG approach enhancing the sustainability of livestock and wildlife in this environment.

IIRS courses Dean of IIRS 13 ENVISAT launched Boudewijn van Leeuwen 15

PLOS ONE, May 16, 2018

Savanna ecosystems are popular subjects for interaction studies. Multiple studies have been done ... more Savanna ecosystems are popular subjects for interaction studies. Multiple studies have been done on the impact of elephants on vegetation, the impact of grass and browse availability on animal densities or on competition between herbivore species. Previous studies showed that elephant densities are frequently negatively correlated with densities of tall trees, and that browse and grass availability are correlated with browser and grazer density respectively. Additionally, a competition effect between browse and grass availability has been reported. These relationships are usually analysed by testing direct relationships between e.g., herbivore densities and food availability, without addressing competition effects or other indirect effects. In this study, multiple interactions in a savanna system have been analysed simultaneously using Partial Least Square-Path Modelling (PLS-PM) using mammal and vegetation data from three different wildlife reserves in southern KwaZulu-Natal. The results showed that the processes that three separate models for the three areas provided the best understanding of the importance of the different interactions. These models suggest that elephants had a negative impact on trees, but also on grass availability. The impact is stronger when elephants are not able to migrate during the dry season. Browsers and grazers were correlated with browse and grass availability, but competition between browse and grass was not detected. This study shows that due to the complexity of the interactions in an ecosystem and differences in environmental factors, these interactions are best studied per area. PLS-PM can be a useful tool for estimating direct, indirect, and cascading effects of changing animal densities in conservation areas.

Nature Ecology & Evolution, 2020

Journal of Applied Ecology, 2016

Functional heterogeneity refers to spatial and temporal variation in the grass height (structure)... more Functional heterogeneity refers to spatial and temporal variation in the grass height (structure), productivity, phenology, composition and chemical attributes of grassland

African Journal of Range & Forage Science

Drought is a natural phenomenon that plays an important role in non-equilibrium disturbance drive... more Drought is a natural phenomenon that plays an important role in non-equilibrium disturbance driven ecosystems. As such, droughts are considered natural and therefore by definition ecologically desirable in many ecosystems (e.g. Frederick and Ogden 2001). However, droughts happen in a particular space-time context, and as such droughts often interact with management activities. These interactions may either reduce or exacerbate drought effects, even in large protected areas (e.g. Walker et al. 1987). It is therefore critical to understand the interplay between drought and management actions in order to inform decision making in protected areas in a future where droughts are expected to become more frequent and intense (Knapp et al. 2008; IPCC 2012). There are four key management actions, all of which influence quantity, quality and/or distribution of key resources, which may influence the effect of droughts on animals, especially in arid or semi-arid protected areas (i.e. MAP <750 mm annum −1): (i) addition or removal of surface water sources (i.e. artificial water provision), (ii) expansion or contraction of area available to herbivores (e.g. consolidation and/or expansion of protected areas and/or migratory corridors), (iii) population control or not (e.g. translocation, culling, contraception) of abundant and/or large-bodied species that have considerable forage requirements, and (iv) addition of forage resources (e.g. provision of supplementary feeding). The following subsections focus on the first three management actions listed above (the fourth management action is neither feasible nor desirable in large protected areas, and as such is not further discussed). Each subsection formulates an adaptive management hypothesis based on current understanding of how the specific management action interacts with drought. An adaptive management hypothesis is essentially a prediction of what is expected to happen (to megaherbivores during a drought in the case of this study) under the different management approaches. This study thereafter sets out to evaluate these hypotheses using spatially explicit long-term

South African Journal of Science

Nature is experiencing degradation and extinction rates never recorded before in the history of E... more Nature is experiencing degradation and extinction rates never recorded before in the history of Earth. 1,2 Consequently, continuous large-scale monitoring programmes are critical, not only to provide insights into population trends but also to aid in understanding factors associated with altering population dynamics at various temporal and spatial scales. 3 Continuous monitoring is important not only for tracking rare or threatened species but also to detect the increase of potentially invasive species 4 , and the trends in the populations of common species, which in some regions are declining even more rapidly than are rare species 2 .

African Journal of Range & Forage Science

African Journal of Range & Forage Science

Journal of the Grassland Society of Southern Africa

Herbaceous plant species composition was measured on ranches in the Thabazimbi district, Transvaa... more Herbaceous plant species composition was measured on ranches in the Thabazimbi district, Transvaal, to obtain veld composition scores and to quantify the relations between such scores and certain determinants considered important in influencing species composition. Determinants investigated were mean annual rainfall and herbivory (stocking rate). The survey was undertaken on seven game and cattle ranches in Combretum apiculatum woodland of

African Journal of Range & Forage Science

European Journal of Wildlife Research, 2015

Elephant Loxodonta africana conservation might indirectly influence the wider herbivore community... more Elephant Loxodonta africana conservation might indirectly influence the wider herbivore community structure, as elephants have the ability to significantly modify the savanna habitat. Uncertainty remains as to the consequences of these effects, as elephants might either compete with other species or facilitate foraging especially for grazers and smaller browsing species by increasing the amount of grass or the amount of browse at lower feeding heights. We studied these potential cascading effects of elephants by using 16 years of data (1992-2011) from the Sabi Sand Wildtuin, South Africa, which showed a steady increase in elephant densities from 0.12 to 2.03 elephants/km 2 over this period. We demonstrate that tree densities, and browse availability at feeding heights below 2 m, decreased with increasing elephant densities, and that there was no positive effect of elephants on browse availability. The changes in elephant densities were good predictors (R 2 adj >0.50) in explaining population fluctuations of other herbivore species. The total body mass of grazers increased more than that of the browsers, shifting the community toward a grazer and megaherbivore-dominated community. An increasing density of elephants changes the composition of the herbivore community, as mesobrowsers are unable to benefit from the impact of elephants on trees, but megagrazers show strong positive responses. Hence, changes in elephant densities as a result of poaching or conservation may trigger cascading community effects. These are neglected but important consequences of (negative or positive) human impacts on elephant numbers, especially in restricted areas such as reserves and national parks.