Large-bodied Herbivores Research Articles

The ecological importance of intact top-predator populations: a synthesis of 15 years of research in a seagrass ecosystem

The worldwide decline of large-bodied marine taxa has made it difficult to draw conclusions about the relative importance of top-down control, and the mechanisms through which it might operate, in coastal marine ecosystems. Since 1997, the Shark Bay Ecosystem Research Project has used the relatively pristine seagrass community of Shark Bay, Australia, to investigate the potential for tiger sharks, the apex predator in the ecosystem, to have an impact on their large-bodied prey through non-consumptive (‘risk’) effects. Here, we synthesise nearly 15 years of data to demonstrate that tiger sharks have widespread risk effects on both large-bodied herbivores and mesopredators in Shark Bay and explore the possibility that these impacts may cascade to lower trophic levels. Although much work remains to be done, our studies suggest that losses of top predators in subtropical estuaries may have greater consequences than generally appreciated and that efforts to conserve and restore their populations should be a priority. Furthermore, future management strategies and studies must explicitly consider the potential for predators to influence behaviour of even large-bodied marine taxa.

The anatomy of the basal ornithischian dinosaur Eocursor parvus from the lower Elliot Formation (Late Triassic) of South Africa

Ornithischia is a morphologically and taxonomically diverse clade of dinosaurs that originated during the Late Triassic and were the dominant large-bodied herbivores in many Cretaceous ecosystems. The early evolution of ornithischian dinosaurs is poorly understood, as a result in part of a paucity of fossil specimens, particularly during the Triassic. The most complete Triassic ornithischian dinosaur yet discovered is Eocursor parvus from the lower Elliot Formation (Late Triassic: Norian–Rhaetian) of Free State, South Africa, represented by a partial skull and relatively complete postcranial skeleton. Here, the anatomy of Eocursor is described in detail for the first time, and detailed comparisons are provided to other basal ornithischian taxa. Eocursor is a small-bodied taxon (approximately 1 m in length) that possesses a plesiomorphic dentition consisting of unworn leaf-shaped crowns, a proportionally large manus with similarities to heterodontosaurids, a pelvis that contains an intriguing mix of plesiomorphic and derived character states, and elongate distal hindlimbs suggesting well-developed cursorial ability. The ontogenetic status of the holotype material is uncertain. Eocursor may represent the sister taxon to Genasauria, the clade that includes most of ornithischian diversity, although this phylogenetic position is partially dependent upon the uncertain phylogenetic position of the enigmatic and controversial clade Heterodontosauridae.

Tissue Nutrient Content in Ulva spp. (Chlorophyceae) as Bioindicator for Nutrient Loading Along the Coast of East Africa

Although macroalgae usually are inconspicuous on pristine coral reefs, they often thrive on reefs that are subjected to various types of anthropogenic disturbance. This thesis consists of five papers and investigates how biomass and composition of macroalgal communities on coral reefs are affected by regulating factors, such as nutrient availability, herbivory, substrate availability and hydrodynamic forces. In addition, ecological functions and potential impacts of both wild and farmed macroalgal communities are evaluated. Paper I describes a method for using macroalgal tissue nutrient concentrations as bioindicator for nutrient availability, with the possibility to map nutrient loading from larger coastal cities. Papers II and III are manipulative studies comparing top-down and bottom-up regulation of macroalgal communities, where herbivore consumption seems to be the main regulator of biomass whereas nutrient availability mainly influences community composition. Exclosure of large-bodied herbivores had a positive influence on algal biomass in both studies, and during different climatic periods. Paper III also includes the influence of hydrodynamic forces on algal community biomass and structure by comparing a reef crest and a back reef-habitat. Alterations of top-down and bottom-up regulation generally had a stronger effect within the protected back reef-habitat, suggesting that such environments may be more sensitive to anthropogenic influence. Paper IV confirms the general conclusions from papers II and III by studying macroalgal biomass and composition on reef sites with different environmental prerequisites. This study also supports the notion that herbivorous fish can suppress accumulation of macroalgal biomass if substrate availability is low, but not where coral cover is reduced and plenty of substrate is open to macroalgal colonization. The study also found a large temporal variation of macroalgal standing stock and associated nutrients at sites with low top-down regulation. Paper V evaluates potential impacts of seaweed farming on coral reefs and nutrients in the seascape by experimentally studying growth, survival and nutrient binding capacity of Eucheuma denticulatum. This study showed that seaweed farms counteract eutrophication through nutrient extraction and that the risk of farmed algae colonizing local reefs seems to be small as they were rapidly consumed. In conclusion, the studies in this thesis contribute to the understanding of macroalgal regulation and function in tropical seascapes, thereby adding to the knowledge base for coastal management.

Isotopic dietary reconstructions of Pliocene herbivores at Laetoli: Implications for early hominin paleoecology

Major morphological and behavioral innovations in early human evolution have traditionally been viewed as responses to conditions associated with increasing aridity and the development of extensive grassland-savanna biomes in Africa during the Plio-Pleistocene. Interpretations of paleoenvironments at the Pliocene locality of Laetoli in northern Tanzania have figured prominently in these discussions, primarily because early hominins recovered from Laetoli are generally inferred to be associated with grassland, savanna or open woodland habitats. As these reconstructions effectively extend the range of habitat preferences inferred for Pliocene hominins, and contrast with interpretations of predominantly woodland and forested ecosystems at other early hominin sites, it is worth reevaluating the paleoecology at Laetoli utilizing a new approach. Isotopic analyses were conducted on the teeth of twenty-one extinct mammalian herbivore species from the Laetolil Beds (∼ 4.3–3.5 Ma) and Upper Ndolanya Beds (∼ 2.7–2.6 Ma) to determine their diet, as well as to investigate aspects of plant physiognomy and climate. Enamel samples were obtained from multiple localities at different stratigraphic levels in order to develop a high-resolution spatio-temporal framework for identifying and characterizing dietary and ecological change and variability within the succession. In general, dietary signals at Laetoli suggest heterogeneous ecosystems with both C 3 and C 4 dietary plants available that could support grassland, woodland, and forested communities. All large-bodied herbivores analyzed yielded dietary signatures indicating mixed grazing/browsing strategies or exclusive reliance on C 3 browse, more consistent with wooded than grassland-savanna biomes. There are no clear isotopic patterns documenting shifting ecology within the Laetolil Beds or between the Laetolil and overlying Upper Ndolanya Beds, although limited data from the U. Ndolanya Beds constrains interpretations. Comparison of the results from Laetoli with isotopic enamel profiles of other African fossil and modern communities reveals significant differences in dietary patterns. Relative to extant taxa in related lineages, carbon isotopic ranges of a number of Laetoli fossil herbivores are anomalous, indicating significantly more generalized intermediate C 3/C 4 feeding behaviors, perhaps indicative of dietary niches and habitat types with no close modern analogs. Enamel oxygen isotope ranges of fossil taxa from Laetoli are consistently more 18O depleted than modern E. African herbivores, possibly indicating more humid conditions during that interval in the past. These data have important implications for reconstructing dietary trajectories of mammalian herbivore lineages, as well as the evolution of ecosystems in East Africa. Isotopic analyses of similar or related taxa at other hominin fossil sites yield signatures generally consistent with Laetoli, suggesting that mammalian communities in East Africa were sampling ecosystems with similar proportions of browse and grass. Collectively, the isotopic dietary signatures indicate heterogeneous habitats with significant wooded or forested components in the Laetoli area during deposition of the Laetolil and Upper Ndolanya Beds. Early hominin foraging activity in this interval may have included access to forest or woodland biomes within this ecosystem, complicating traditional interpretations linking early human evolutionary innovations with a shift to savanna habitats.

The first record of a Cretaceous dinosaur from southwestern Alaska

Cretaceous dinosaurs are recorded for the first time from southwestern Alaska by a series of three tracks found in Aniakchak National Monument. This trackway is in the Upper Cretaceous (Campanian–Maastrichtian) Chignik Formation, a cyclic sequence of marine to non-marine clastic sedimentary rocks. The nearest coeval locality is approximately 1500 km northeast of this site, along the Colville River in northern Alaska, which contains abundant dinosaurs. This distance helps to document the occurrence of a widespread Cretaceous Arctic terrestrial ecosystem that supported significant numbers of large-bodied herbivores.

Dietary reconstruction of Miocene Gomphotherium (Mammalia, Proboscidea) from the Great Plains region, USA, based on the carbon isotope composition of tusk and molar enamel

The Miocene of the Great Plains of North America has long been recognized as an interval of major ecological reorganization. To reconstruct the dietary response of the proboscidean Gomphotherium to Miocene ecosystem change in the Great Plains, we analyzed the carbon isotope composition of 185 serial samples of tusk enamel from 17 individuals and bulk samples of posterior molars from 15 individuals of Gomphotherium from localities in the Great Plains ranging in age from the Early Barstovian land mammal age (ca. 15 Ma) to the Early Hemphillian land mammal age (ca. 8 Ma). Sets of samples from each tusk were designed to encompass about 1 year of tusk growth. Based on cheek tooth morphology, Gomphotherium is thought to be a browser with a diet primarily of dicots. The mean δ 13C of all samples is −9.8±1.2‰, indicating that the diet of Gomphotherium was dominated by C 3 biomass. If Gomphotherium habitually foraged on water-stressed plants in arid habitats, which would have δ 13C values higher than the average composition for C 3 and C 4 plants, then all but one individual in this study consumed less than 50% C 4 biomass. The maximum percentage of C 4 in the diet would be much lower if food plants had average δ 13C values or if Gomphotherium foraged in closed-canopy habitats. Differences in δ 13C values between specimens from the southwestern US and the Great Plains, as well as between some coeval specimens from Nebraska, suggest geographic differences in either diet or typical foraging habitat. The data do not indicate a trend toward inclusion of more C 4 vegetation in the diet of Gomphotherium during the Miocene, and none of the serially sampled tusks exhibit seasonally varying δ 13C profiles. For most of its history in North America, Gomphotherium was a C 3 browser or a mixed feeder with a preference for browse. Our results indicate that areas of wooded habitat sufficient to support herds of large-bodied herbivores remained available in the Great Plains through the Late Miocene.

Algal growth and species composition under experimental control of herbivory, phosphorus and coral abundance in Glovers Reef, Belize

The proliferation of algae on disturbed coral reefs has often been attributed to (1) a loss of large-bodied herbivorous fishes, (2) increases in sea water nutrient concentrations, particularly phosphorus, and (3) a loss of hard coral cover or a combination of these and other factors. We performed replicated small-scale caging experiments in the offshore lagoon of Glovers Reef atoll, Belize where three treatments had closed-top (no large-bodied herbivores) and one treatment had open-top cages (grazing by large-bodied herbivores). Closed-top treatments simulated a reduced-herbivory situation, excluding large fishes but including small herbivorous fishes such as damselfishes and small parrotfishes. Treatments in the closed-top cages included the addition of high phosphorus fertilizer, live branches of Acropora cervicornis and a third unmanipulated control treatment. Colonization, algal biomass and species composition on dead A. palmata “plates” were studied weekly for 50 days in each of the four treatments. Fertilization doubled the concentration of phosphorus from 0.35 to 0.77 μM. Closed-top cages, particularly the fertilizer and A. cervicornis additions, attracted more small-bodied parrotfish and damselfish than the open-top cages such that there was moderate levels of herbivory in closed-top cages. The open-top cages did, however, have a higher abundance of the chemically and morphologically defended erect algal species including Caulerpa cupressoides, Laurencia obtusa, Dictyota menstrualis and Lobophora variegata. The most herbivore-resistant calcareous green algae (i.e. Halimeda) were, however, uncommon in all treatments. Algal biomass increased and fluctuated simultaneously in all treatments over time, but algal biomass, as measured by wet, dry and decalcified weight, did not differ greatly between the treatments with only marginally higher biomass ( p<0.06) in the fertilized compared to open-top cages. Algal species composition was influenced by all treatments with a maximum between-treatment Bray–Curtis similarity of only 29%. The fertilized cages showed rapid colonization by a mixed turf community largely composed of the filamentous brown ( Hincksia mitchelliae) and green ( Enteromorpha prolifera) species. Algal cover in the fertilized cages leveled at 80% after 20 days compared to less than 50% in the other treatments. There was no evidence that A. cervicornis suppressed algal colonization compared to the unmanipulated controls. Instead, the herbivore susceptible Padina sanctae-crucis was the most abundant algae followed by Jania capillacea in this treatment in contrast to the more chemically defended Dictyota menstrualis that dominated the unmanipulated controls. We conclude that A. cervicornis was not suppressing algae as a group and its loss cannot account for the observed changes in algal abundance in most reefs except for creating space. In contrast, A. cervicornis appears to attract aggressive damselfish that may reduce herbivory by larger herbivores. Phosphorus enrichment can lead to rapid colonization of space by filamentous turf communities but not high biomass and dominance of erect frondose algae within 50 days. Moderate levels of herbivory by large-bodied herbivores promoted moderately herbivore-resistant erect brown and green algae that are commonly reported on disturbed reefs. Consequently, all the studied factors influenced algal communities but seldom as commonly predicted.

Limnological changes in a sub‐tropical shallow hypertrophic lake during its restoration: two years of a whole‐lake experiment

Abstract1. Lake Rodó is a turbid system, a condition attributed to algal biomass. The proximal source of the eutrophication was stormwater discharges from an ill‐defined urban area. This paper describes an attempt to restore the water quality of Lake Rodó, the first time this has been done in Uruguay. In spring 1996 it was drained, sediments were removed and stream inputs were diverted. Groundwater was used to re‐fill the lake. Due to its high nutrient concentration a re‐circulation system was designed, pumping water from associated pools covered with free‐floating plants.2. After the lake was refilled, the system was characterized by oxygen saturation or over‐saturation, neutral to basic pH, and high phosphorus, nitrogen and silicate concentrations. Ratios of total nitrogen (TN):total phosphorus (TP) and chlorophyll a (Chl a):TP indicated that phosphorus was the primary limiting nutrient during the period of groundwater supply. Once groundwater pumping had ceased, there was a decrease in TN:TP and Chl a:TP ratios, suggesting N‐limiting conditions prevailed in some periods.3. Before restoration, the phytoplankton community was dominated year‐round by Planktothrix agardhii; since restoration the community has been more diverse. This change has favoured grazing by mesozooplankton, and the onset of clear‐water phases in spring.4. Abundant populations of small omnivorous fish maintained a high predation pressure on zooplankton, restricting the abundance of large‐bodied herbivores, which, in turn, allowed an increase in phytoplanton biomass and a decrease in water transparency. Based on this observation, together with the phosphorus concentration and the low abundance of filamentous cyanobacteria compared with previous studies, we suggest that top‐down control has played a key role in increasing transparency in Lake Rodó.5. A nutrient reduction programme, by the mechanical harvest of floating plants, and a removal of small omnivorous fishes and stocking strictly with piscivores, could be key factors in the achievement of a stable clear‐water phase. However, if blooms of Microcystis or other similar genera occur in summer, additional measures (e.g. reduction of the hydraulic residence time) will be needed to improve water transparency.Copyright © 2001 John Wiley &amp; Sons, Ltd.

High-precision 40Ar/39Ar geochronology and the advent of North America's Late Cretaceous terrestrial fauna.

A densely sampled, diverse new fauna from the uppermost Cedar Mountain Formation, Utah, indicates that the basic pattern of faunal composition for the Late Cretaceous of North America was already established by the Albian-Cenomanian boundary. Multiple, concordant 40Ar/39Ar determinations from a volcanic ash associated with the fauna have an average age of 98.39 +/- 0.07 million years. The fauna of the Cedar Mountain Formation records the first global appearance of hadrosaurid dinosaurs, advanced lizard (e.g., Helodermatidae), and mammal (e.g., Marsupialia) groups, and the first North American appearance of other taxa such as tyrannosaurids, pachycephalosaurs, and snakes. Although the origin of many groups is unclear, combined biostratigraphic and phylogenetic evidence suggests an Old World, specifically Asian, origin for some of the taxa, an hypothesis that is consistent with existing evidence from tectonics and marine invertebrates. Large-bodied herbivores are mainly represented by low-level browsers, ornithopod dinosaurs, whose radiations have been hypothesized to be related to the initial diversification of angiosperm plants. Diversity at the largest body sizes (>10(6) g) is low, in contrast to both preceding and succeeding faunas; sauropods, which underwent demise in the Northern hemisphere coincident with the radiation of angiosperms, apparently went temporarily unreplaced by other megaherbivores. Morphologic and taxonomic diversity among small, omnivorous mammals, multituberculates, is also low. A later apparent increase in diversity occurred during the Campanian, coincident with the appearance of major fruit types among angiosperms, suggesting the possibility of adaptive response to new resources.

Ancient feeding ecology and niche differentiation of Pleistocene mammalian herbivores from Tarija, Bolivia: morphological and isotopic evidence

The exceedingly rich middle Pleistocene mammalian fauna from the classic Ensenadan Tarija basin in southern Bolivia contains a diversity of medium to large-bodied herbivores consisting of both endemic (†Toxodontia, †Litopterna, Xenarthra) and immigrant (Rodentia, Proboscidea, Perissodactyla, and Artiodactyla) taxa. In order to characterize feeding ecology and niche differences, a suite of morphological characters was measured for each of 13 species of herbivorous mammals from the Pleistocene of Tarija; these were combined with carbon isotopic results from tooth enamel. (The Xenarthra were excluded from this study because they lack tooth enamel.)Several different bivariate and multivariate combinations of characters can be used to characterize the feeding adaptations, niches, and guild composition of the Tarija mammalian herbivores. During the Pleistocene the browsing guild in the Tarija basin is interpreted to include the tapir (Tapirus tarijensis), extinct llama (Palaeolama weddelli), peccary (Tayassusp.), and deer (Hippocamelussp.). The mixed-feeding guild included two horse species (Hippidion principaleandOnohippidium devillei), litoptern (Macrauchenia patachonica), and capybara (Neochoerus tarijensis). The grazing guild included the numerically dominant horse (Equus insulatus), two lamine species (Lama angustimaxillaand cf.Vicugna, provicugna), notoungulate (Toxodon platensis), and gomphothere proboscidean (Cuvieronius hyodon). The grazing guild has the widest range of body sizes relative to the two other guilds. Closely related sympatric species within the Equidae and Camelidae differentiate their niches from one another using a combination of body size, feeding ecology, and probably local habitat. Most of the paleoecological reconstructions resulting from this combined morphological and isotopic analysis corroborate previous studies based primarily on morphology; there are, however, some notable surprises.

Feeding and Chewing Behaviours of Nubian Ibex: Compensation for Sex-Related Differences in Body Size

Size-related differences in digestive capabilities are thought to account for patterns of diet selection, social structure and habitat use by small- and large-bodied herbivores. We examined food processing behaviours that could compensate for digestive constraints resulting from the relative scaling of metabolic requirements and gut capacity with body mass. We observed feeding, chewing and ruminating behaviours of sexually size-dimorphic Nubian ibex fed diets chopped to a short (1-2 cm), medium (8 cm), or long (25 cm) length. These diets differed in the amount of oral processing needed for particle size reduction, bolus formation and swallowing. Food particle size did not affect intake rate (g/min) but chewing investment (chews/g) of both sexes was 30% less for the shortest hay. Rumination activity of both sexes approximated the maximum sustainable level of almost 10h/day for all diets. Chewing rates (chews/min) during rumination did not differ between males and females. Chewing investment of females was 40% greater than that of males while feeding and more than 50% greater while ruminating. Size-related differences in molar occlusal surface area (∼ 15%) were much too small to account for sex-related variation in chewing investment. Our results support the hypothesis that females enhanced digestion rates relative to those of larger-bodied males through increased oral processing.

Taphonomy and Paleoecology of the Dinosaur Beds of the Jurassic Morrison Formation

The Upper Jurassic Morrison Formation has yielded one of the richest dinosaur faunas of the world. Morrison sediments are distributed over more than a million square kilometers in the western United States and represent a mosaic of riverine, lacustrine and floodplain environments developed on a vast alluvial plain nourished by debris from the ancestral Rocky Mountains. Plant productivity must have been reasonably high to support abundant large-bodied herbivores, but the absence of coals, scarcity of small aquatic vertebrates, the abundance of oxidized sediments, and presence of calcretes lead us to believe that water was periodically in short supply. A strongly seasonal climate may have necessitated annual large-scale movements of large herbivores, accounting in part for their remarkably broad and uniform geographic distribution. Dinosaur diversity is lower in the Morrison than in the Late Cretaceous, and taphonomic alteration is higher. Massed accumulations of thousands of bones are characteristic of the Morrison. Morrison dinosaurs were not confined to specific depositional environments but were distributed across the complete spectrum of available habitats, from lakes to dry floodplains; this type of distribution is similar to that of large terrestrial mammals such as elephants and rhinos and is different from that of hippos and crocodiles. Common Morrison taxa wereCamarasaurus, Apatosaurus, Diplodocus, AllosaurusandStegosaurus;these genera probably constituted a true dinosaur community.Stegosaurusmay have been partially segregated from the other genera, andCamptosaurusmore strongly so.CamarasaurusandDiplodocuswere gregarious, with juveniles and subadults of the former particularly common;Apatosauruswas less abundant and more solitary in its habits. Juveniles and subadults are known for a number of dinosaurs.

Taphonomy and Paleoecology of the Dinosaur Beds of the Jurassic Morrison Formation

The Upper Jurassic Morrison Formation has yielded one of the richest dinosaur faunas of the world. Morrison sediments are distributed over more than a million square kilometers in the western United States and represent a mosaic of riverine, lacustrine and floodplain environments developed on a vast alluvial plain nourished by debris from the ancestral Rocky Mountains. Plant productivity must have been reasonably high to support abundant large-bodied herbivores, but the absence of coals, scarcity of small aquatic vertebrates, the abundance of oxidized sediments, and presence of calcretes lead us to believe that water was periodically in short supply. A strongly seasonal climate may have necessitated annual large-scale movements of large herbivores, accounting in part for their remarkably broad and uniform geographic distribution. Dinosaur diversity is lower in the Morrison than in the Late Cretaceous, and taphonomic alteration is higher. Massed accumulations of thousands of bones are characteristic of the Morrison. Morrison dinosaurs were not confined to specific depositional environments but were distributed across the complete spectrum of available habitats, from lakes to dry floodplains; this type of distribution is similar to that of large terrestrial mammals such as elephants and rhinos and is different from that of hippos and crocodiles. Common Morrison taxa wereCamarasaurus, Apatosaurus, Diplodocus, AllosaurusandStegosaurus;these genera probably constituted a true dinosaur community.Stegosaurusmay have been partially segregated from the other genera, andCamptosaurusmore strongly so.CamarasaurusandDiplodocuswere gregarious, with juveniles and subadults of the former particularly common;Apatosauruswas less abundant and more solitary in its habits. Juveniles and subadults are known for a number of dinosaurs.