Paleolithic Dietary Flexibility? Methodological Considerations in Analogy-Based Reconstructions of Paleolithic Energetic Returns

Large mammalian herbivores are vital components of terrestrial ecosystems, influencing the plants they feed on, but also serving as ecosystem engineers that impact the occurrence and survival of many other organisms. Arthropods are the most abundant and diverse animal group on earth, filling all trophic levels in food webs and facilitating essential ecosystem services. However, the impacts of large herbivores on arthropod communities and the mechanisms via which these impacts are mediated are not fully understood. Here, we experimentally separated the mechanistic pathways whereby large herbivores affect arthropod food webs using a 24‐year manipulative multi‐site field experiment in the Netherlands. We analysed the abundance, biomass and community composition of arthropods in the plant canopy and on the soil surface, both in grazed sites or sites where large herbivores were excluded. We found that the presence of large herbivores resulted in considerable differences in vegetation properties and microclimate which influenced the abundance and biomass of arthropods to varying trophic levels. Large herbivore grazing enhanced the overall abundance and biomass of arthropod herbivores, pollinators, omnivores and soil‐dwelling predators, but reduced that of detritivores, scavengers, parasitoids and canopy predators. Structural equation models revealed that different trophic groups are affected by grazing via different pathways. Specially, large herbivores facilitated herbivores via increasing plant quality and enhanced ground‐dwelling predators via increasing plant diversity. In contrast, plant‐dwelling predators were suppressed via decreased plant quantity, and parasitoids were mainly affected by changes in microclimate conditions. Synthesis. Our results show that large mammalian herbivores play a significant role in shaping grassland arthropod food webs, and that these impacts were independently mediated by multiple aspects of vegetation properties, that is, physical structure, plant diversity, standing crop biomass and leaf nutrient content. Arthropods of different trophic groups responded differently to the large herbivores, and these functional group‐specific responses in turn may have strong cascading effects on numerous ecosystem services.

This study aimed at evaluating the energetic return and feeding time on Philodryas nattereri kept in captivity. Snakes were fed biweekly for 60 days (four feeding trials), in two different feeding treatments (single and multiple prey items). The energetic return revealed no significant difference between the feeding treatments; however, we found a negative relationship between snake size and prey handling time during a feed using multiple prey items. In P. nattereri , when large preys are as easy to find as small ones, there seems to be no difference in energetic return.

IntroductionThe use of fire marks a critical milestone in human evolution, with its initial purposes debated among scholars. While cooking is often cited as the primary driver, this study proposes that meat and fat preservation, and predator protection were more likely the initial motivations for fire use by Homo erectus during the Lower Paleolithic (1.9–0.78 Ma).MethodsEmploying a bioenergetic approach, we compared the energetic returns of hunting versus plant gathering using ethnographic data, adjusted for Lower Paleolithic conditions. Caloric content of East African prey was calculated to assess consumption duration. Archeological evidence from early fire sites was analyzed for associations with large fauna.ResultsHunting large prey (>100 kg) yielded significantly higher energetic returns (16,269 ca/h) than plant gathering (1,443 ca/h), with megaherbivores like hippopotamus providing sustenance for up to 22 days for a group of 25. Early fire sites consistently contained large fauna remains, suggesting prolonged prey consumption. Cooking offered modest energetic gains (e.g., ~1,200 ca/h for meat), insufficient to offset fire maintenance costs, unlike preservation and protection.DiscussionThe substantial energetic disparity supports hunting as a dominant subsistence strategy, with fire enhancing efficiency by preserving meat and deterring predators. The prevalence of megaherbivores in Lower Paleolithic sites and heightened predation risks underscore these priorities over cooking, which likely emerged as a secondary benefit. Ethnographic analogies underrepresent these dynamics due to megafaunal extinctions altering the environment and prey availability.ConclusionMeat preservation and predator protection, rather than cooking, were likely the primary drivers of early fire use, aligning with Homo erectus’ specialization in large prey acquisition. This reframes fire’s role in human evolution, suggesting it supported a hypercarnivorous lifestyle and potentially influenced cognitive development.

What are infochemicals?Chemical compounds play an important role in interactions between organisms. Some of these chemicals are to the benefit (e.g. nutrients) or detriment (e.g. toxins) of an organism. Others are of benefit or detriment in an indirect way: through the behavioural response they elicit. The latter chemicals are termed infochemicals (chemicals that, in the natural context, convey information in an interaction between two individuals, evoking in the receiver a behavioural or physiological response that is adaptive to either one of the interactants or both; chapter 2). On an evolutionary time scale, the fate of an infochemical depends on selection pressures on each interactant. Selection pressure is determined by costs and benefits which result from all interactions of an organism in which the infochemical is involved. Yet, for pragmatic reasons, to analyse the function of an infochemical in the biology of an organism, a cost-benefit analysis is made for each interaction between two organisms separately. In this way the cost-benefit analysis is restricted to the smallest number of interactants possible, which ensures its simplicity. Consequently, for each interaction the infochemical is classified according to the corresponding costs and benefits for the two interactants (chapter 2; cf. Nordlund and Lewis, 1976). Moreover, classification also reflects whether the interaction under consideration is between conspecifics or between individuals of different species. This resulted in the terminology represented in Figure 1.1 and Table 1.1 (cf. chapter 2). Its structure and terms are based on those of semiochemicals. However, infochemical terminology differs from semiochemical terminology in two respects (chapter 2):(1) Infochemical terminology regards compounds that convey information, whereas semiochemical terminology in addition also includes toxins (Whittaker and Feeny, 1971; Nordlund and Lewis, 1976; Nordlund, 1981). In some instances toxins or nutrients may convey information. If that is the case, these toxins and nutrients are classified as infochemicals when their role as information carrier is considered. When poisonous or nutritious aspects are considered, they are not classified as infochemicals, but as toxins and nutrients respectively.(2) Semiochemical terminology is based on origin of the compounds, in addition to the cost-benefit analysis. Although knowledge of the origin is Important to understand the interaction between two organisms, it may be very difficult to elucidate the origin (e.g. Brand et al., 1975; chapter 4). Therefore, application of the origin criterion may lead to ambiguities. Because the cost- benefit criterion by itself is good and useful, infochemical terminology is based on that criterion alone.Infochemicals in tritrophic systems.Infochemicals play a role in interactions between consecutive trophic levels (e.g plant-herbivore, phytophagous insect- entomophagous insect; Figure 1.2) (e.g. Nordlund et al., 1981; Visser, 1986). Moreover, infochemicals may also mediate interactions between other trophic levels (e.g. plant-entomophagous insect; Figure 1.2) (Price, 1981). Therefore, to understand the selection pressure on an organism, as a result of an infochemical, all trophic levels involved should be regarded. As a consequence, investigations of infochemicals in interactions between herbivores and their predators should also regard involvement of at least the first trophic level, the plant.The tritrophic system of this study: predatory mites, phytophagous mites and their host plants.The herbivore-predator system investigated most extensively in this thesis consists of phytophagous mites and predatory mites that occur in Dutch orchards. Figure 1.3a,b depicts the two most abundant phytophagous mites that occur as pest organisms in Dutch apple orchards: the apple rust mite, Aculusschlechtendali (Nalepa), and the European red spider mite, Panonychusulmi (Koch) (Van de Vrie, 1973; Van Epenhuijsen, 1981; Gruys, 1982).Several species of predatory mites occur in Dutch orchards. The most abundant of these are Typhlodromuspyri Scheuten (Figure 1.3c), Amblyseiusfinlandicus (Oudemans) and A.potentillae (Garman) (McMurtry & Van de Vrie, 1973; Overmeer, 1981; Gruys, 1982). All three species feed on P.ulmi and A.schlechtendali , as well as on other food sources such as several pollens (Overmeer, 1981; Kropczynska, 1970; Overmeer, 1985).In this system consisting of two phytophagous prey species and three predator species (Figure 1.4a), prey preference of the predators was investigated. Optimal foraging theory predicts that natural selection favours predators preferring prey species that are most profitable in terms of reproductive success (Krebs, 1978). Reproductive success is determined, among others, by development time, oviposition rate, mortality during development and offspring quality. Each of these components can be affected by the prey species consumed. As a first step in analysing which selection pressures may have moulded prey preference of the predatory mites in the system outlined above, I have tested whether prey preference is matched by the associated reproductive success. If this most simple explanation for prey preference does not hold, other explanations should be considered (see below).Do infochemicals play a role in prey preference ?Kairomones (Table 1.1, Figure 1.1) may inform predators on presence and identity of prey (Greany and Hagen, 1981) and thereby affect foraging decisions, such as where to search, how long to search at a specific site, which prey to accept and when to disperse on air currents (chapter 3).Investigation of the response to kairomones may therefore yield information on prey preference. However, the conclusion on prey preference must be restricted to the foraging phase that was studied. Relative costs involved in finding individuals of each prey species might differ for different foraging phases. Therefore, to obtain a comprehensive view of prey preference, several foraging phases should be investigated. Such analyses should be carried out independently to obtain complementary conclusions. In this study, prey preference was determined in three independent analyses.Two laboratory analyses were carried out:- Analysis of response towards volatile kairomones. This investigation regards decisions of the predators when prey individuals are not contacted, as is the situation after termination of aerial dispersal or after eradication of a prey patch.- Analysis of predation rates at different prey supplies. This relates to acceptance/rejection decisions during contacts with prey items.To complement the prey preference analyses carried out in the laboratory, an investigation was made under field conditions: - This was done by determination of diet composition by means of electrophoretic analysis of gut contents of field-collected predators.Spider-mite kairomones in a tritrophic context.Predatory mites distinguish plants infested by spider mites from clean plants by a volatile kairomone (e.g. Sabelis & Van de Baan, 1983). This kairomone seems to be a product of the interaction between plant and spider mites: after removal of spider mites from an infested plant, the plant remains attractive to the predators during several hours, whereas the mites alone do not remain attractive (Sabelis & Van de Baan, 1983; Sabelis et al., 1984a). Current data on spider mite - predatory mite interactions do not explain the role of this infochemical in the biology of the spider mites (cf. chapter 3 for a review). It may, for instance, be an inevitable byproduct of damage inflicted on the plant by the spider mite, and/or have an indispensable function in the biology of the spider mite. Moreover, the plant may be involved in production of the infochemical. To elucidate the role of this volatile infochemical, its effects in interactions between plant and spider mite, between plant and predatory mite and between spider mites of one species should be investigated. Before this can be done, chemical identification of the infochemical is a necessary first step.These investigations were made for a tritrophic system consisting of Lima bean plants, the two-spotted spider mite, Tetranychusurticae Koch and the predatory mite Phytoseiuluspersimilis Athias-Henriot (Figure 1.4b). This system was chosen for practical reasons. The plant and phytophagous mite can be reared throughout the year and therefore, this system is much more suitable to develop a method for the chemical analysis of spider-mite kairomones than a system in which the plant is a perennial.Origin and function of T.urticae kairomone in a tritrophic system.Two-spotted spider mites distinguish between a clean plant and a plant that is infested by conspecifics on the basis of a volatile infochemical (chapter 4). The spider mites move away from heavily infested leaves. This response is advantageous to spider mites on the infested leaf as well as to spider mites that avoid settling on these leaves: increased competition for food is avoided, cf. Wrensch and Young (1978). In addition, the spider mite that disperses thus avoids settling on a spot that has an increased risk of being detected by predatory mites (Sabelis and Van de Baan, 1983). Therefore, the infochemical in this interaction between conspecific spider mites is called a (+,+)dispersing pheromone. Biological evidence suggests that this pheromone is (at least partly) identical to the volatile kairomone to which predatory mites respond (chapter 4).Volatiles emitted from plants infested by T.urticae were identified and subsequent behavioural analyses resulted in identification of four kairomone components that attract the predatory mite P.persimilis : linalool (3,7-dimethyl-1,6-octadiene- 3-ol), methyl salicylate, ( E )-β-ocimene (3,7-dimethyl-1,3( E ),6- octatriene) and 4,8-dimethyl-1,3( E ),7-nonatriene. The structure of these compounds is shown in Figure 1.5. At least two of these (linalool and methyl salicylate) are also components of a kairomone in the interaction between T.urticae and A.potentillae (when reared on V.faba pollen; see below) (chapter 4). Literature data on the behavioural response of T.urticae indicate that one of these kairomone components (linalool) is also a component of the (+,+)dispersing pheromone (Dabrowski and Rodriguez, 1971).All identified kairomone components are well-known in the plant kingdom. This suggests that the plant is involved in production of the infochemical, but it is no proof. It may for Instance be that spider-mite enzymes injected into the plant break down a plant compound. Investigation of e.g. site and moment of production and possible storage of precursors are needed as a next step to elucidate the role of the plant in kairomone production. However, suppose that it is the spider mite who produces the infochemical to serve as a dispersing pheromone. Then, it is not clear why this pheromone should necessarily consist of volatiles. As a result of the production of volatiles the spider mites incur more risks of being detected by predators than by production of non-volatile chemicals. Detection by predators inevitably leads to local extermination of spider mites (Sabelis and Van der Meer, 1986). For this reason it seems more likely that the volatiles are plant produced and that the spider mite makes the best of a bad job by using them as information to decide where not to colonize. To understand the evolution of plant-produced volatiles after herbivore attack, it is crucial to assess how they are produced, how much it costs to produce them and what the benefits are in terms of a lowered probability of herbivore attack.Involvement of volatile kairomones in prey preference of predatory mites.The response of T.pyri and A.potentillae to volatile kairomones is dependent on the diet of the predators. When reared on a carotenoid-poor diet these predators respond to the kairomones of more prey species than when reared on a carotenoid-rich diet (chapters 6, 7 and 8). Carotenoids are indispensable to A.potentillae because of their function in diapause induction (Overmeer, 1985a). The function of these nutrients to T.pyri remains unknown (chapter 8). All prey species to whose kairomones carotenoid-deficient A.potentillae and T.pyri respond can relieve the lack of carotenoids. Carotenoid-containing A.potentillae and T. pyri only respond to the P.ulmi kairomone. The above observations were made for predators that were starved for 20 h. Longer starvation of predators reared on a carotenoid-rich diet also enlarges the number of prey species responded to. Investigations of the response to volatile kairomones indicates that A.potentillae and T.pyri (whether carotenoids are available or not) prefer P.ulmi to A.schlechtendali (chapters 6, 7 and 8) and that A.finlandicus has a reverse preference (chapter 11).This corresponds to conclusions from predation experiments performed at different composition of prey supply (chapters 9 and 11). The observed predation rates when mixed prey supplies were offered, were compared with a model provided with parameters estimated from experiments with each of both prey species alone. Amblyseiuspotentillae and T.pyri fed more on P.ulmi and A.finlandicus fed more on A.schlechtendali than was predicted by the model. This difference between observed and predicted predation rates cannot be explained by a change in behaviour of the prey species as a result of being together, nor by a change in walking behaviour of the predator. Therefore, these data indicate that A. potentillae and T.pyri prefer P.ulmi and that A.finlandicus prefers A.schlechtendali , in terms of a change in acceptance/rejection ratio ('success ratio').Analysis of prey preference under field conditions showed that most T.pyri collected from apple leaves that widely varied in P.ulmi : A.schlechtendali numbers contained P.ulmi esterase, whereas A.schlechtendali esterase was present in a minor fraction of predators (chapter 10). Rust-mite esterase and P.ulmi esterase were found equally frequent in A.finlandicus . The data for A.finlandicus , obtained over a narrower range of prey-number ratios than for T.pyri , do not allow a definite conclusion on prey preference. However, they certainly do not cause rejection of the conclusion on prey preference as obtained in the laboratory analyses (chapter 11). No field data are available for A.potentillae .Because the conclusions on prey preference as determined in these independent analyses are consistent for each predator species, the inference on prey preference is firmly established.Prey preference and reproductive success of predatory mites in an orchard system with two species of phytophagous prey mites.Analysis of reproductive success of these three predator species, when feeding on either P.ulmi or A.schlechtendali , indicates that A.finlandicus selects the best prey species in terms of reproductive success. This predator species suffers high larval mortality on P.ulmi , but not on A.schlechtendali . This results in a much higher intrinsic rate of population increase when feeding on apple rust mites (chapter 12).Amblyseiuspotentillae and T.pyri would also do better by feeding preferentially on A.schlechtendali : development times when feeding on this prey species are shorter than when feeding on P.ulmi , whereas these prey species do not differentially affect mortality or oviposition rate (chapter 12). For A.potentillae this may not be the case at the end of the season because P.ulmi is a better prey species in terms of diapause induction. Thus, on the basis of current data, optimal prey-choice theory cannot satisfactorily predict actual prey peference of A.potentillae and T.pyri . Future investigations should concentrate on e.g. (1) possible effect of competition between prey species on prey availability, (2) possible effect of competition between predator species on prey availability, and (3) possible shift in prey preference during the season.

We performed a meta‐analysis of 31 lake mesocosm experiments to investigate differences in the responses of pelagic food chains and food webs to nutrient enrichment and fish presence. Trophic levels were divided into size‐based functional groups (phytoplankton into highly edible and poorly edible algae, and zooplankton into small herbivores, large herbivores and omnivorous zooplankton) in the food webs. Our meta‐analysis shows that 1) nutrient enrichment has a positive effect on phytoplankton and zooplankton, while fish presence has a positive effect on phytoplankton and a negative effect on zooplankton in the food chains; 2) nutrient enrichment has a positive effect on highly edible algae and small herbivores, but no effect on poorly edible algae, large herbivores and omnivorous zooplankton in the food webs. Planktivorous fish have a positive effect on highly edible algae and small herbivores, a negative effect on large herbivores and omnivorous zooplankton, and no effect on poorly edible algae. Our meta‐analysis confirms that nutrient enrichment and planktivorous fish affect functional groups differentially within trophic levels, revealing important changes in the functioning of food webs. The analysis of fish effects shows the well‐described trophic cascade in the food chain and reveals two trophic cascades in the food web: one transmitted by large herbivores that benefit highly edible phytoplankton, and one transmitted by omnivorous zooplankton that benefit small herbivores. Comparison between the responses of food webs and simple food chains also shows consistent biomass compensation between functional groups within trophic levels.

Picky carnivorous plants? Investigating preferences for preys' trophic levels - a stable isotope natural abundance approach with two terrestrial and two aquatic Lentibulariaceae tested in Central Europe.

Changing prey size preferences in the annual cycle of Retusa obtusa (Montagu) (Opisthobranchia) feeding on Hydrobia ulvae (Pennant) (Prosobranchia)

Explaining prehistoric variation in the abundance of large prey: A zooarchaeological analysis of deer and rabbit hunting along the Pecho Coast of Central California

There is established concern that loss of biodiversity will affect ecosystem productivity, nutrient cycling, carbon storage, stability and other properties^1,2^. Interactions between trophic levels are thought to link changes to biodiversity and ecosystem processes^3-6^. However, there is a lack of empirical studies linking plant diversity with altered trophic levels^7,8^, especially for large herbivores, the important but often neglected, controlling trophic level in terrestrial systems. Here we examine responses in performance of the large generalist herbivore to changes in plant diversity, using an indoor cafeteria trial and a field experiment. Our results show that increased plant diversity improves herbivore performance but it is depressed at highest plant diversity levels. We propose the Disturbance Selection Hypothesis for explaining plant diversity effects on primary consumers. Increasing the number of plant species in grassland, increases consumption and enhances nutrient intake (presumably improving animal fitness) by modifying nutrient balance, toxin dilution and taste modulation. High plant diversity simultaneously intensifies animal diet switching frequency, and weakens the herbivore's ability to select food, thereby increasing foraging cost and disturbing the herbivore's selection of forage. Thus, the consequence of plant diversity for large herbivore performance depends on the trade-off between the positive and negative effects. At highest plant diversity the positive effects weaken and negative effects strengthen. We suggest knowledge of the mechanisms is the means for understanding relationships between biodiversity and ecosystem functioning, and the management of large herbivores on rangelands used for conservation and grazing.

Effects of food web complexity on top-down control in tropical lakes

The exceptional diversity of large mammals in African savannas provides an ideal opportunity to explore the relative importance of top‐down and bottom‐up controls of large terrestrial herbivore communities. Recent work has emphasized the role of herbivore and carnivore body size in shaping these trophic relationships. However, the lack of across‐ecosystem comparisons using a common methodology prohibits general conclusions. Here we used published data on primary production, herbivore and carnivore densities and diets to estimate the consumption fluxes between three trophic levels in four African savanna ecosystems. Our food web approach suggests that the body size distribution within and across trophic levels has a strong influence on the strength of top‐down control of herbivores by carnivores and on consumption fluxes within ecosystems, as predicted by theoretical food web models. We generalize findings from the Serengeti ecosystem that suggest herbivore species below 150 kg are more likely to be limited by predation. We also emphasize the key functional role played by the largest species at each trophic level. The abundance of the largest herbivore species largely governs the consumption of primary production in resident communities. Similarly, predator guilds in which the largest carnivore species represent a larger share of carnivore biomass are likely to exert a stronger top‐down impact on herbivores. Our study shows how a food web approach allows integrating current knowledge and offers a powerful framework to better understand the functioning of ecosystems.

Large-scale patterns of isotope ratios are detectable in the tissues of organisms, but the variability in these patterns often obscures detection of environmental trends. We show that plants and animals at lower trophic levels are relatively poor indicators of the temporal trend in atmospheric carbon isotope ratios (delta13C) when compared with animals at higher trophic levels. First, we tested how differences in atmospheric delta13C values were transferred across three trophic levels. Second, we compared contemporary delta13C trends (1961-2004) in atmospheric CO2 to delta13C patterns in a tree species (jack pine, Pinus banksiana), large herbivore (moose, Alces alces) and large carnivore (grey wolf, Canis lupus) from North America. Third, we compared palaeontological (approx. 30000 to 12000 14C years before present) atmospheric CO2 trends to delta13C patterns in a tree species (Pinus flexilis, Juniperus sp.), a megaherbivore (bison, Bison antiquus) and a large carnivore (dire wolf, Canis dirus) from the La Brea tar pits (southern California, USA) and Great Basin (western USA). Contrary to previous expectations, we found that the environmental isotope pattern is better represented with increasing trophic level. Our results indicate that museum specimens of large carnivores would best reflect large-scale spatial and temporal patterns of carbon isotopes in the palaeontological record because top predators can act as ecological integrators of environmental change.

Large herbivores can affect vegetation structure and species composition as well as material and energy flows in the ecosystem through their selective feeding, defecation, urination and trampling. These changes have a large potential to indirectly affect other trophic levels, but the mechanisms are poorly known. We studied the impacts of moose Alces alces browsing along a gradient of site productivity by experimentally simulating four different moose densities. Here we show that moose can affect the richness and abundance of three trophic levels in Swedish boreal forests through complex direct and indirect impacts, but in qualitatively different ways depending on how the physical habitat or food resources of a trophic level are affected. Vegetation richness had a hump‐shaped (unimodal) response to increased moose density. Leaf litter production decreased when browsing increased, which in turn depressed the abundance of flying prey for spiders. Consequently, spider abundance and richness declined monotonically. The responses of spider richness to moose density were further conditioned by site productivity: the response was positive at productive and negative at unproductive sites. In contrast, herbivorous Hemiptera were not affected by moose, most likely because the abundance of their food plants was not affected. The highest simulated moose density had an impact on all variables responding to moose even after a few years of treatment and can be considered as overabundance. We also show that the impacts of low or moderate moose density can be positive to some of the organisms negatively affected by high density. The level of herbivore population density that leads to substantial community impacts also depends on site factors, such as productivity.

The central organizing theme of this paper is to discuss the dynamics of the Serengeti grassland ecosystem from the perspective of recent developments in food-web theory. The seasonal rainfall patterns that characterize the East African climate create an annually oscillating, large-scale, spatial mosaic of feeding opportunities for the larger ungulates in the Serengeti; this in turn creates a significant annual variation in the food available for their predators. At a smaller spatial scale, periodic fires during the dry season create patches of highly nutritious grazing that are eaten in preference to the surrounding older patches of less palatable vegetation. The species interactions between herbivores and plants, and carnivores and herbivores, are hierarchically nested in the Serengeti food web, with the largest bodied consumers on each trophic level having the broadest diets that include species from a large variety of different habitats in the ecosystem. The different major habitats of the Serengeti are also used in a nested fashion; the highly nutritious forage of the short grass plains is available only to the larger migratory species for a few months each year. The longer grass areas, the woodlands and kopjes (large partially wooded rocky islands in the surrounding mosaic of grassland) contain species that are resident throughout the year; these species often have smaller body size and more specialized diets than the migratory species. Only the larger herbivores and carnivores obtain their nutrition from all the different major habitat types in the ecosystem. The net effect of this is to create a nested hierarchy of subchains of energy flow within the larger Serengeti food web; these flows are seasonally forced by rainfall and operate at different rates in different major branches of the web. The nested structure that couples sequential trophic levels together interacts with annual seasonal variation in the fast and slow chains of nutrient flow in a way that is likely to be central to the stability of the whole web. If the Serengeti is to be successfully conserved as a fully functioning ecosystem, then it is essential that the full diversity of natural habitats be maintained within the greater Serengeti ecosystem. The best way to do this is by controlling the external forces that threaten the boundaries of the ecosystem and by balancing the economic services the park provides between local, national and international needs. I conclude by discussing how the ecosystem services provided by the Serengeti are driven by species on different trophic levels. Tourism provides the largest financial revenue to the national economy, but it could be better organized to provide more sustained revenue to the park. Ultimately, ecotourism needs to be developed in ways that take lessons from the structure of the Serengeti food webs, and in ways that provide tangible benefits to people living around the park while also improving the experience of all visitors.

Mollusc shells, commonly preserved in archaeological records worldwide, capture high-resolution, sub-annual environmental information at local scales through the incorporation of chemical elements during their formation. These geochemical signals can be used to infer the season of shellfish collection by past human populations. This study presents new seasonal data derived from magnesium-to-calcium (Mg/Ca) ratios in Patella caerulea Linnaeus, 1758 from the archaeological site of Haua Fteah in northern Cyrenaica (Libya, North Africa). Our data were obtained through elemental mapping using laser induced breakdown spectroscopy (LIBS), which enables the visualisation of intra-shell geochemical variation at high spatial resolution. The results provide detailed reconstructions of shellfish collection seasonality from the Capsian to the Neolithic periods, covering a ∼5,000 year span from the latest Pleistocene through the Early-Mid Holocene. We demonstrate that mollusc gathering occurred throughout the year, with a higher frequency in the autumn and winter seasons, suggesting that marine resource use was more consistent than previously assumed. We compare our data with previous seasonality studies of different mollusc species to demonstrate that seasonal collection patterns varied between mollusc species, suggesting differences in marine exploitation subsistence strategies, probably related to the availability of other food resources, energetic return and mollusc processing techniques.