Does Foraging or the Avoidance of Predation Determine Habitat Selection by Selective Resident Grazers in the Serengeti Woodlands? A Mixed Strategy with Season
Simple Summary
Abstract
1. Introduction
1.1. Food Hypothesis
- (1)
- The resident ungulates do not stay in the same plant community and move down the catena towards the rivers in the dry season in order to select swards with large quantities of grass in view of their capacity to select high quality food from this type of sward (see [22] page 91, Figure 3.11 and [8]).
- (2)
- In the wet season, grass is abundant everywhere, so the structure of the swards is less predictive of habitat selection than in the dry season and the relation is non-linear ([22] page 91, Figure 3.11).
- (3)
- After passage through the study area by the migrants in the dry season, the quantity of food available is reduced. The residents continue to select habitats with larger quantities of grass. They move further down the catena compared to before the passage of the migrants to compensate for the change in quantity and structure of the swards.
- (4)
- The habitats selected in the dry season differ in grass species from those selected in the wet due to their different location on the catena. Since the animals’ mechanisms of food selection (particularly their mouth sizes) are unchanged, the preferred swards in each season have similar structures.
1.2. Predation Hypothesis
- (1)
- The ungulates should select open vegetation types and avoid ones with thicker cover. They should avoid vegetation types with large quantities of grass in both seasons.
- (2)
- In the wet season the risk of predation remains higher near thicker cover so ungulate distributions should be unchanged compared to the dry season.
2. Materials and Methods
2.1. Field Methods and Study Area
2.2. Analysis
2.2.1. The Seasons
2.2.2. Selectivity by the Ungulates
2.2.3. Habitat Variables
3. Results
3.1. Habitat Selection by the Selective Resident Grazers Along the Soil Catena
3.2. Plant Structure Along the Soil Catena
3.3. Plant Structure in the Swards Selected by the Ungulates
3.4. Impact of the Migrants on the Sward Choices of the Resident Selective Grazers
3.5. Predation Risk and Habitat Selection
3.6. Abundance of Topi and Kongoni—Impact of the Migrants
4. Discussion
4.1. Habitat Selection by Resident, Selective Grazers in Savanna Habitats; The Processes
4.2. Impact of the Migrants on the Abundance of the Resident Selective Grazers
5. Conclusions
Supplementary Materials
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Based on the Facets in a Landscape Classification of the Serengeti National Park ([31] and K. Gerresheim pers.comm.). | ||||||
---|---|---|---|---|---|---|
Facet | Vegetation Type | Morphology | Common Woody Plants | Dominant Grasses | Area % | Predation Risk |
9a | VT1 | Upper part of wide, gently concave plains, very well drained | Mostly grassland with sparse, Vachellia tortilis and patches, of Senegalia mellifera | Sporobolus marginatus, Digitaria macroblephara, S. pellucidus, Panicum coloratum | 11.7 | Less risky |
4, 5b | VT 2 | Elongated interfluve ridges, gently rounded and very well drained | V.robusta, V. tortilis, V. hockii, S. senegal, Commiphora, schimperae | Chloris roxburghiana, D. macroblephara, Bothriochloa insculpta, S. marginatus | 35.2 | Intermediate |
1b | VT 3 | Isolated rounded hills | V. hockii, S. senegal, | Eustachys paspaloides, Heteropogon contortus | 14.4 | Intermediate |
5, 5a | Ormocarpum trichocarpum | S. fimbriatus, D. macroblephara, Themeda triandra | ||||
9b | VT 4 | Middle concave plains, well drained | Open grassland with, some V. drepanolobium | T. triandra, P. coloratum, Microchloa kunthii, S. festivus | 7.8 | Less risky |
9b | VT 5 | Lower concave plains, | V. drepanolobium, some V. tortilis | Cenchrus mezianus, T. triandra, P. coloratum, | 24.1 | Risky |
11, 13 | fairly well drained | B. insculpta, Cymbopogon excavatus | ||||
9c, 14a, 14b | VT 6 | Shallow elongated drainage lines and minor valleys, ephemeral surface drainage. | V. tortilis, V. robusta, Albizia harveyi, some V. seyal and Kigelia africana | T. triandra, P. mezianum, Chloris gayana, Sorghum verticilliflorum, P. coloratum, Echinochloa haploclada | 6.8 | Risky |
Restricted variables—four were measured in 18 months: |
Biomass of the herb layer, leaf height, culm height and culm density. |
Nine variables were measured in 11 of the 18 months: |
Weight of grass green leaf |
Weight of grass dry leaf |
Weight of grass stem and sheath |
Length of leaves of the dominant grass species |
Length of leaves of the other grass species. |
From these three composite variables were calculated: |
% green leaf in the sward |
% dry leaf in the sward |
% stem and sheath in the sward |
a. Dry seasons | ||||
Principal Component | PC1 | PC2 | PC3 | PC4 |
Green leaf % | −0.385 | −0.667 | 0.541 | 0.333 |
Dry leaf % | 0.237 | −0.831 | −0.472 | −0.173 |
Stem % | 0.000 | 0.993 | 0.111 | −0.026 |
Sward biomass (log) | 0.969 | 0.071 | 0.055 | −0.131 |
Leaf height (log) | 0.929 | −0.009 | 0.032 | 0.251 |
Culm height (log) | 0.704 | 0.191 | −0.454 | 0.478 |
Culm density (log) | 0.952 | −0.038 | −0.013 | 0.103 |
Green leaf biomass (log) | 0.826 | −0.257 | 0.444 | −0.010 |
Dry leaf biomass (log) | 0.908 | −0.303 | 0.014 | −0.239 |
Stem biomass (log) | 0.918 | 0.292 | 0.206 | −0.159 |
b. Wet seasons | ||||
Principal Component | PCR1 | PCR2 | ||
Sward biomass (log) | 0.960 | −0.02 | ||
Leaf height (log) | 0.897 | −0.37 | ||
Culm height (log) | 0.960 | −0.01 | ||
Culm density (log) | 0.889 | 0.429 |
a. Dry Seasons—from the Full Analysis of the Swards. | |
Principal Component | % of variance |
PC1 | 57.6 |
PC2 | 24.1 |
PC3 | 9.8 |
PC4 | 5.4 |
Total | 96.9 |
b. Wet seasons—from the analysis of the restricted set of sward variables. | |
Principal Component | % of variance |
PCR1 | 86.4 |
PCR2 | 8.0 |
PCR3 | 3.5 |
PCR4 | 2.1 |
Total | 100.0 |
PC1, PC2, PC3, PC4—The Scores on the First Four Principal Components. | |||
---|---|---|---|
Species | Dry Seasons | Variance Explained (%) | Significance (p) |
Kongoni | Preference = 1.26 + 0.189 PC1 + 0.625 PC3 − 0.886 PC4 | 82 | <0.001 |
Topi (all) | Preference = 1.23 + 0.214 PC1 − 0.803 PC4 + 0.498 PC3 | 79 | <0.001 |
Topi (breeding) | Preference = 1.30 + 0.294 PC1 + 0.686 PC3 | 92 | <0.001 |
Topi (males) | Preference = 1.29 + 0.188 PC1 − 0.680 PC4 + 0.743 PC3 | 80 | <0.001 |
Buffalo | Preference = 1.23 + 0.383 PC1 | 34 | <0.01 |
Zebra | Preference = 0.854 − 0.065 PC1 | 24 | <0.05 |
Wildebeest | Preference = 0.959 − 0.053 PC1 | 13 | <0.10 |
Thomson’s gazelle | Preference = 0.966 − 0.117 PC1 | 16 | <0.10 |
Prediction equations for habitat selection in the wet seasons. | |||
PCR1—The score on the first Principal Component (‘Herb layer Quantity’) from the analysis of the restricted set of sward variables. | |||
Topi (all) | Preference = 1.90 − 0.186 PCR1 − 0.0875 PCR12 + 0.012 PCR13 | 27 | <0.01 |
Kongoni | Preference = 1.51 − 0.115 PCR1 − 0.0657 PCR12 + 0.0082 PCR13 | 25 | <0.01 |
Species | Component | Variance Explained (%) |
Kongoni | PC1 | 54 |
PC3 | 17 | |
PC4 | 11 | |
Topi (all) | PC1 | 64 |
PC3 | 8 | |
PC4 | 7 | |
Topi (breeding) | PC1 | 79 |
PC3 | 13 | |
Topi (males) | PC1 | 44 |
PC3 | 24 | |
PC4 | 12 | |
Buffalo | PC1 | 34 |
Zebra | PC1 | 24 |
Wildebeest | PC1 | 13 |
Thomson’s gazelle | PC1 | 16 |
a. On the Biomass | ||||||||||||
Short grass swards | g/m2 | Medium height swards | g/m2 | |||||||||
Before | 95% cl | After | 95% cl | Reduction % | Before | 95% cl | After | 95% cl | Reduction % | |||
Woodlands | 1971 | 110 | 25 | 15 | 9 | 86.4 | 170 | 21 | 40 | 15 | 76.5 | |
All swards | Before | |||||||||||
Woodlands | 1972 | 195 | 31 | 75 | 30 | 61.5 | ||||||
Medium height swards | ||||||||||||
Western plains | 1974 | 457 | 69 | 84.9 | ||||||||
b. On the leafiness of the grass | ||||||||||||
All swards | Leaf/Stem + Sheath ratio | |||||||||||
Woodlands | 1971 | Before | After | Reduction % | ||||||||
1.23 | 0.4 | 67.5 | ||||||||||
Woodlands | 1972 | Before | After | |||||||||
1.5 | 0.33 | 78.0 |
1971 | Topi | Kongoni | Rain mm, Monthly | Season | Grass Biomass (g/m2) | |
13, 18 February | 188, 136 | 189, 175 | 36 | ‘Wet’ | Not measured | |
March | 140 | 176 | 23 | ‘’ | Not measured | |
May | 132 | 172 | 188 | ‘’ | 173 | |
1st June | 40 | 32 | c. 25 000 wildebeest | ‘Dry’ | Not measured | |
11 June | 89 | 71 | c.100 Wbst, c.2600 Zebra, >100 Gazelles. | 2 | ‘’ | 50 |
July | 129, 129 | 62, 83 | On 23rd c.200 Wbst, c.90 Zebra. >100 Gazelles both dates. | 49 | ‘’ | Not measured |
15, 23 August | 57, 114 | 31, 74 | On 15th no Wbst or Zebra, hundreds of Gazelles & Buffalo. on 23rd no Wbst, <50 Zebes in gps of <10, hundreds of TG, no Buff. | 25 | ‘’ | Not measured |
3 September | 150 | 144 | >2000 Wbst,>1000 Gazelles, >200 Zebras. | ‘’ | Not measured | |
24 September | 139 | 71 | <100 Wbst,>1000 Gazelles, 4 Zebras, 250 Buffalo. | 8 | ‘’ | Not measured |
25 October | 162 | 135 | No Wbst, >100 Gazelles, <10 Zebra, 250 Buffalo. | 101 | ‘’ | 66 |
29 November | 105 | 69 | No Wbst, Gazelles; >100 Zebra. | 57 | ‘Dry’ | 51 |
December | 174 | 156 | No Wbst, <20 Gazelles; 145 Zebra, 18 Buffalo. | 52 | ‘Wet’ | 92 |
1972 | ||||||
January | No count | No count | 23 | ‘Wet’ | Not measured | |
February | 162 | 106 | No Wbst, 6 Gazelles; c. 100 Zebra. | 143 | ‘’ | 101 |
March | 192 | 213 | No migrants | 76 | ‘’ | 131 |
April | 128 | 110 | Zebra moving thro, Wbst in smallish herds, <500 | 72 | ‘’ | 104 |
May | No count | No count | Zebra moving thro, then Wbst, strong impact on grass. | 108 | ‘’ | 62 |
8 June | 114 | 25 | 500 Wbst, tens of zebras, no Gazelles. | 132 | ‘’ | 78 |
2nd July | 129 | 205 | No Wbst, 2000 Zebra, 5 Gazelles, 380 Buffalo. | 0 | ‘’ | 98 |
August | No count | No count | 72 | ‘Dry’ | 31 | |
9 September | 79 | 85 | c. 400 Wbst, c.800 Zebra, c. 1000 Gazelles | 86 | ‘’ | 57 |
October | 149 | 70 | c. 1700 Wbst, c.250 Zebra, c. 350 Gazelles, 31 Buffalo. | 56 | ‘’ | 57 |
23 November | 223 | 214 | 6 Wbst, c.350 Zebra, no Gazelles, 49 Buffalo. | 185 | ‘’ | 64 |
December | No count | No count | 206 | ‘Wet’ | 102 | |
1973 | No count | No count | ||||
January | No count | No count | 79 | Not measured | ||
February | No count | No count | 72 | Not measured | ||
March | No count | No count | 10 | Not measured | ||
27 April | 178 | 204 | c. 500 Wbst, c.2000 Zebra, c. 1000 Gazelles | 49 | ‘Wet’ | 116 |
May | No count | No count | 83 | Not measured | ||
June | No count | No count | 24 | Not measured | ||
July | No count | No count | 0 | Not measured | ||
August | No count | No count | 20 | Not measured | ||
18 September | 241 | 210 | c. 700 Wbst, c.400 Zebra, c. 600 Buffalo, c.350 Gazelles | 175 | ‘Dry’ | 68 |
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Duncan, P.; Sinclair, A.R.E. Does Foraging or the Avoidance of Predation Determine Habitat Selection by Selective Resident Grazers in the Serengeti Woodlands? A Mixed Strategy with Season. Animals 2025, 15, 2202. https://doi.org/10.3390/ani15152202
Duncan P, Sinclair ARE. Does Foraging or the Avoidance of Predation Determine Habitat Selection by Selective Resident Grazers in the Serengeti Woodlands? A Mixed Strategy with Season. Animals. 2025; 15(15):2202. https://doi.org/10.3390/ani15152202
Chicago/Turabian StyleDuncan, Patrick, and Anthony R. E. Sinclair. 2025. "Does Foraging or the Avoidance of Predation Determine Habitat Selection by Selective Resident Grazers in the Serengeti Woodlands? A Mixed Strategy with Season" Animals 15, no. 15: 2202. https://doi.org/10.3390/ani15152202
APA StyleDuncan, P., & Sinclair, A. R. E. (2025). Does Foraging or the Avoidance of Predation Determine Habitat Selection by Selective Resident Grazers in the Serengeti Woodlands? A Mixed Strategy with Season. Animals, 15(15), 2202. https://doi.org/10.3390/ani15152202