Hominid paleoecology and competitive exclusion: Limits to similarity,niche differentiation,and the effects of cultural behavior

Fossil evidence from the Plio-Pleistocene of Africa apparently has confirmed a multi-lineage interpretation of early hominid evolution. Empirical refutation of the single species hypothesis must now be matched to the evolutionary ecology theory, which can underwrite taxonomic assessment and help to explain sympatric hominid coexistence. This paper contributes to that goal by reassessing the ecological rationale provided for the single-species hypothesis. Limiting similarity concepts indicate that the allowable ecological overlap between sympatric competitors is greater than the degrees of metric overlap often advanced as standards for identifying fossil species. Optimal foraging theory and the compression hypothesis show that the initial ecological reaction of a hominid to a sympatric competitor would likely be micro-habitat divergence and possibly also temporal differentiation of resource use. The long-term, evolutionary response is niche divergence, probably involving diet as well. General niche partitioning studies suggest that diet and habitat are the most common dimensions of niche separation, although temporal separation is unusually frequent in carnivores. The equation of niche with culture, basic to the single-species hypothesis, has no analytic meaning. Finally, four minor points are discussed, suggesting that (a) extinction is not unlikely, even for a long-lived and competitively competent hominid lineage, (b)parsimony is fickle, (c)interspecific mutualism may jeopardize survival, and (d)generalists are subordinate competitors, but for hominids, seemingly, successful ones. I argue that analog models of hominid paleoecology should be replaced by the use of zoological and anthropological observations to assess the generality and reliability of ecological theory and comcepts that may encompass early hominids.     

Resource partitioning in sympatric langurs and macaques in tropical rainforests of the central Western Ghats, south India

In a competitive sympatric association, coexisting species may try to reduce interspecific interactions as well as competition for similar resources by several ecological and behavioral practices. We studied resource utilization of three sympatric primate species namely, lion-tailed macaques (Macaca silenus), bonnet macaques (M. radiata) and Hanuman langurs (Semnopithecus entellus) in a tropical rainforest of the central Western Ghats, south India. We studied resource use, tree-height use, foraging height, substrate use when consuming animal prey and interspecific interactions. The results revealed that across the year, there was very limited niche overlap in diet between each species-pair. Each primate species largely depended on different plant species or different plant parts and phenophases from shared plant species. Primate species used different heights for foraging, and the two macaque species searched different substrates when foraging on animal prey. We also recorded season-wise resource abundance for the resources shared by these three primate species. While there was low dietary overlap during the dry season (a period of relatively low resource abundance), there was high dietary overlap between the two macaque species during the wet season (a period of high resource abundance for the shared resources). We observed only a few interspecific interactions. None of these were agonistic, even during the period of high niche overlap. This suggests that the sympatric primate species in this region are characterized by little or no contest competition. Unlike in some other regions of the Western Ghats, the lack of interspecific feeding competition appears to allow these primates, especially the macaques, to remain sympatric year-round.     

Parallel evolution of ecomorphological traits in the European whitefish Coregonus lavaretus (L.) species complex during postglacial times

The extensive phenotypic polymorphism in the European whitefish has triggered evolutionary research in order to disentangle mechanisms underlying diversification. To illuminate the ecological distinctiveness in polymorphic whitefish, and evaluate taxonomic designations, we studied nine Norwegian lakes in three watercourses, which each harboured pairs of divergent whitefish morphs. We compared the morphology and life history of these morphs, documented the extent of genetic differentiation between them, and contrasted the niche use of sympatric morphs along both the habitat and resource axes. In all cases, sympatric morphs differed in the number of gill rakers, a highly heritable trait related to trophic utilization. Individual growth rate, age and size at maturity, diet and habitat use also differed between morphs within lakes, but were remarkably similar across lakes within the same morph. Microsatellite analyses confirmed for all but one pair that sympatric morphs were significantly genetically different, and that similar morphs from different lakes likely have a polyphyletic origin. These results are most compatible with the process of parallel evolution through recurrent postglacial divergence into pelagic and benthic niches in each of these lakes. We propose that sparsely and densely rakered whitefish sympatric pairs may be a likely case of ecological speciation, mediated in oligotrophic lakes with few trophic competitors.     

Synecology of Bornean primates. I. A test for interspecific interactions in spatial distribution of five species

In a 15-month study of anthropoid primates in the forest of eastern Borneo, observers made 1230 contacts with groups of five different species within a study area of approximately 3 km². A test of the hypothesis that there is no effect on the presence of one species by the presence of another (using the method of partial correlation) shows that in every pair of species the presence of one has a negative effect on the presence of the other, and that in seven of ten pairs the hypothesis may be rejected at the 97% level of confidence or better. Three cases in which the hypothesis cannot be rejected are found to have biological meaning: behavioral data show that niche separation of the pairs of species is such that their distributions should be independent. In spite of widely divergent feeding and locomotor adaptations, it is apparent that the species are competing for use of the forest.     

Testing the role of climate in speciation: New methods and applications to squamate reptiles (lizards and snakes)

Climate may play important roles in speciation, such as causing the range fragmentation that underlies allopatric speciation (through niche conservatism) or driving divergence of parapatric populations along climatic gradients (through niche divergence). Here, we developed new methods to test the frequency of climate niche conservatism and divergence in speciation, and applied it to species pairs of squamate reptiles (lizards and snakes). We used a large‐scale phylogeny to identify 242 sister species pairs for analysis. From these, we selected all terrestrial allopatric pairs with sufficient occurrence records (n = 49 pairs) and inferred whether each originated via climatic niche conservatism or climatic niche divergence. Among the 242 pairs, allopatric pairs were most common (41.3%), rather than parapatric (19.4%), partially sympatric (17.7%), or fully sympatric species pairs (21.5%). Among the 49 selected allopatric pairs, most appeared to have originated via climatic niche divergence (61–76%, depending on the details of the methods). Surprisingly, we found greater climatic niche divergence between allopatric sister species than between parapatric pairs, even after correcting for geographic distance. We also found that niche divergence did not increase with time, further implicating niche divergence in driving lineage splitting. Overall, our results suggest that climatic niche divergence may often play an important role in allopatric speciation, and the methodology developed here can be used to address the generality of these findings in other organisms.     

Resource partitioning of sympatric small mammals in an African forest‐grassland vegetation mosaic

It is often hypothesized that two species competing for the same resource cannot stably coexist unless they partition their resources in space and time. More recently stable isotope analyses have complemented traditional, observation‐based niche research by conceptualizing many of the characteristics of communities, for example, trophic niche width and the partitioning of resources. Here we quantify resource partitioning of sympatric small mammal species in an African ecosystem by analysing stable isotope ratios of hair collected from a South African forest‐grassland vegetation mosaic, and combine this with known spatial and temporal behavioural data to interpret community competition and resource partitioning. We observe niche separation to different degrees across the entire community, with different species displaying either unique isotopic dietary preferences, or partitioning resources in space and/or time. δ¹³C values were more enriched in species that inhabited afromontane grassland compared with those that inhabited afromontane forest, a reflection of the dominant vegetation in each habitat. Contrary to expectations, arboreal rodents occupied higher trophic positions than terrestrial rodents and approaching δ¹⁵N values similar to insectivorous shrews, suggesting that arboreal rodents feed on items such as arthropods enriched in ¹⁵N. While grassland species display phenotypic plasticity in terms of dietary preferences, small mammals that occurred in forests display narrow niche preferences, suggesting these species may be particularly sensitive to habitat modifications. Our results illustrate that the use of stable isotopes can be used in conjunction with spatial and temporal behavioural knowledge to elucidate resource partitioning in small African mammal communities.     

Trade‐offs in seedling growth and survival within and across tropical forest microhabitats

For niche differences to maintain coexistence of sympatric species, each species must grow and/or survive better than each of the others in at least one set of conditions (i.e., performance trade‐offs). However, the extent of niche differentiation in tropical forests remains highly debated. We present the first test of performance trade‐offs for wild seedlings in a tropical forest. We measured seedling relative growth rate (RGR) and survival of four common native woody species across 18 light, substrate, and topography microhabitats over 2.5 years within Hawaiian montane wet forest, an ideal location due to its low species diversity and strong species habitat associations. All six species pairs exhibited significant performance trade‐offs across microhabitats and for RGR versus survival within microhabitats. We also found some evidence of performance equivalence, with species pairs having similar performance in 26% of comparisons across microhabitats. Across species, survival under low light was generally positively associated with RGR under high light. When averaged over all species, topography (slope, aspect, and elevation) explained most of the variation in RGR attributable to microhabitat variables (51–53%) followed by substrate type (35–37%) and light (11–12%). However, the relative effects of microhabitat differed among species and RGR metric (i.e., RGR for height, biomass, or leaf area). These findings indicate that performance trade‐offs among species during regeneration are common in low‐diversity tropical forest, although other mechanisms may better explain the coexistence of species with small performance differences.     

Habitat use and support preference of two free-ranging saltatory lemurs (Lepilemur edwardsi and Avahi occidentalis)

Lepilemur edwardsi and Avahi occidentalis are two species of nocturnal, folivorous 'vertical clingers and leapers' (VCL). They have a similar body mass and share the same morphological adaptation for leaping. In a field study under sympatric conditions at Ampijoroa, Madagascar, comparison of support use with support availability using Jacobs' D preference values (Jacobs, 1974) showed that both species actively chose or avoided branches with certain qualities. However, while both species showed a preference for small oblique and horizontal branches, they selected them at different heights in the forest and with varying degrees of preference and avoidance for the other available supports. Despite their traditional locomotor assignation, both species showed a surprisingly strong preference for horizontal supports. These striking variations in detail of support preference may aid the maintenance of species segregation and niche difference.     

Ecological niche modeling of the sympatric giant and red pandas on a mountain-range scale

Habitat use and separation between the two sympatric species, the giant panda and the red panda, have been primary causes of coexistence at the fine scale. In this paper, we addressed the question of coexistence between species in space. By Ecological Niche Factor Analysis, we calculated species-specific habitat requirements, built habitat suitability maps and examined interspecific differences in spatial niche parameters. According to the ENFA scores, suitable habitats in the giant and red panda are surrounded by high-altitude, and are rich in conifer forest. Compared with the giant panda, however, the red panda rather preferred sparse forests, and normally colonized far from village and road. Despite similar narrow niche breadth for both pandas, difference of niche overlap indices implied that the width of environmental niche of red pandas almost completely encompasses that of the giant panda. We, therefore, suggest that differences in use of ecological niche variables may contribute to coexistence of the sympatric species in space. Based on highly suitable locations of the sympatric species maps, most official reserves appear to be poorly located or are too small, and new reserves are recommended to be established in the central part of core habitats in the Liangshan Mountains.     

山西绵山植被优势种群生态位研究

应用Shannon-Weaver指数和Portraitis方法,研究了山西绵山植被优势种群的生态位宽度、生态位普遍重叠和特定重叠,结果表明：(1)乔木层中辽东栎生态位宽度最大（2.458 7）;灌木层中山桃（2.342 2）和土庄绣线菊（2.306 1）生态位宽度最大;草本层中披针苔草（2.518 7）和山蒿（2.218 2）生态位宽度最大。这主要由于这些物种的生态幅较宽,是绵山植被的主要建群种或优势种,对环境具有广泛的适应性;(2)群落中25个优势种群之间并不存在完全的普遍重叠,说明这些植物各自具有不尽相同的生物学特性及生态适应性;(3)乔木层物种除辽东栎与其它植物间具有一定的重叠之外,其它乔木间生态位重叠较少;灌木层中六道木与土庄绣线菊生态位重叠值最大（0.663）,其次是山桃和胡枝子（0.587）;草本植物中披针苔草与糙苏（0.339）、铁杆蒿与山蒿（0.245）表现出较大的特定重叠。种对间生态位重叠值越大,表明它们彼此间具有较为相似的生物学特性和生态适应性,反之亦然。如六道木与土庄绣线菊、披针苔草与糙苏,它们均为耐荫植物,具有一定程度的耐荫性;而山桃和胡枝子、山蒿与铁杆蒿则为喜阳耐旱植物。     

塔里木河中下游地区荒漠河岸林群落种间关系分析

采用 2× 2列联表, 应用Fisher精确检验法研究了新疆塔里木河中下游荒漠河岸林群落种间关系, 测定了16种植物、共 12 0个种对的种间联结性。研究结果表明 :1) 12 0个种对中有 17个种对分别在不同的样方尺度中表现出显著或极显著的种间联结, 约占总数的 14.2 % ;其中 13个种对为正关联, 4个种对为负关联 ;2 ) 不同取样面积对种间联结性分析的有效性有影响, 不同种对表现出种间联结的最小样方尺度不同 ;3) 随着样方面积的增大, 各种对自有不同的种间联结变化规律, 可归纳为 4种类型 ;4 ) 17个具种间联结的种对以灌木草本和草本草本的种对居多, 占总数的 76.5 % ;主要乔木树种胡杨 (Populuseuphratica) 与灌木之间、灌木和灌木之间趋向独立分布。     

Niche differences between two sympatric whiptail lizards (Cnemidophorus abaetensis and C. ocellifer, Teiidae) in the restinga habitat of northeastern Brazil.

Differences among sympatric lizard species usually result from differences in the use of three resources: space, time and food or some combination of these three. However, differences in resource utilization among sympatric species may simply reflect their specific ecological needs rather than competitive pressures. In this study, we analyzed the temporal, spatial and food niche of two congeneric teiids (Cnemidophorus abaetensis and C. ocellifer) living sympatrically in the "restinga" habitat of Abaeté in the Salvador Municipality, Bahia State, Brazil to assess the degree of niche differentiation among them. The whiptail species overlapped considerably in an hourly activity (Ojk = 0.93), in microhabitat use (Ojk = 0.97) and in the prey items consumed (Ojk = 0.89). Differences in amount of vegetation in the microhabitats used by both lizard species may have contributed to differences in the activity period and in the distribution of the main prey eaten by these lizards which may, in turn, facilitate their coexistence in Abaeté. Although sympatric C. ocellifer and C. abaetensis in Abaeté differed only slightly in their use of microhabitats, period of activity and diet, the most important niche dimension segregating the two species seemed to be the food niche.     

A framework for testing assumptions about foraging scales,body mass,and niche separation using telemetry data

Ecological theory predicts that if animals with very similar dietary requirements inhabit the same landscape, then they should avoid niche overlap by either exploiting food resources at different times or foraging at different spatial scales. Similarly, it is often assumed that animals that fall in different body mass modes and share the same body plan will use landscapes at different spatial scales. We developed a new methodological framework for understanding the scaling of foraging (i.e. the range and distribution of scales at which animals use their landscapes) by applying a combination of three well‐established methods to satellite telemetry data to quantify foraging patch size distributions: (1) first‐passage time analysis; (2) a movement‐based kernel density estimator; and (3) statistical comparison of resulting histograms and tests for multimodality. We demonstrate our approach using two sympatric, ecologically similar species of African ducks with quite different body masses: Egyptian Geese (actually a shelduck), and Red‐billed Teal. Contrary to theoretical predictions, the two species, which are sympatric throughout the year, foraged at almost identical spatial scales. Our results show how ecologists can use GPS tracking data to explicitly quantify and compare the scales of foraging by different organisms within an animal community. Our analysis demonstrates both a novel approach to foraging data analysis and the need for caution when making assumptions about the relationships among niche separation, diet, and foraging scale.     

Bridge under troubled water: Turbulence and niche partitioning in fish foraging

The coexistence of competing species relies on niche partitioning. Competitive exclusion is likely inevitable at high niche overlap, but such divide between competitors may be bridged if environmental circumstances displace competitor niches to enhance partitioning. Foraging‐niche dimension can be influenced by environmental characteristics, and if competitors react differently to such conditions, coexistence can be facilitated. We here experimentally approach the partitioning effects of environmental conditions by evaluating the influence of water turbulence on foraging‐niche responses in two competing fish species, Eurasian perch Perca fluviatilis and roach Rutilus rutilus, selecting from planktonic and benthic prey. In the absence of turbulence, both fish species showed high selectivity for benthic chironomid larvae. R. rutilus fed almost exclusively on zoobenthos, whereas P. fluviatilis complemented the benthic diet with zooplankton (mainly copepods). In turbulent water, on the other hand, the foraging‐niche widths of both R. rutilus and P. fluviatilis increased, while their diet overlap simultaneously decreased, caused by 20% of the R. rutilus individuals turning to planktonic (mainly bosminids) prey, and by P. fluviatilis increasing foraging on littoral/benthic food sources. We show that moderate physical disturbance of environments, such as turbulence, can enhance niche partitioning and thereby coexistence of competing foragers. Turbulence affects prey but not fish swimming capacities, with consequences for prey‐specific distributions and encounter rates with fish of different foraging strategies (pause‐travel P. fluviatilis and cruise R. rutilus). Water turbulence and prey community structure should hereby affect competitive interaction strengths among fish species, with consequences for coexistence probability as well as community and system compositions.     

黑龙江省胜山林场冬季驼鹿、马鹿和狍的种间关系

1987—1989年的两个冬季在黑龙江省黑河市胜山林场,对驼鹿、马鹿和狍的食性、采食高度和栖息地进行了研究。驼鹿的主要食物是柳(22.4％)、榛(16.0％)、红松(14.3％)和桦(13.8％);马鹿为杨(36.0％)、桦(22.7％)和红松(17.3％);狍为桦(26.5％)、柳(19.0％)、杨(12.7％)。三种动物采食高度的频次为正态分布。驼鹿的采食高度(标准差)为137.4(±39.0)厘米;马鹿为136.2(±37.0)厘米;狍为84.2(±29.2)厘米。驼鹿和马鹿对红松林的利用程度最高,而狍主要利用沼泽植物和红松林。驼鹿与狍在食物维和栖息地维上的生态位重叠最大,驼鹿与马鹿在采食高度维上的重叠最大。三种动物在食物、采食高度和栖息地三维生态位上的重叠大小的顺序为:驼鹿和马鹿>驼鹿和狍>马鹿和狍。     

Switching from negative to positive density-dependence among populations of a cobble beach plant

Understanding the co-occurrence of ecologically similar species remains a puzzling issue in community ecology. The species-rich mouse lemurs (Microcebus spec.) are distributed over nearly all remaining forest areas of Madagascar with a high variability in species distribution patterns. Locally, many congeneric species pairs seem to co-occur, but only little detailed information on spatial patterns is available. Here, we present the results of an intensive capture-mark-recapture study of sympatric Microcebus berthae and M. murinus populations that revealed small-scale mutual spatial exclusion. Nearest neighbour analysis indicated a spatial aggregation in Microcebus murinus but not in M. berthae. Although the diet of both species differed in proportions of food categories, they used the same food sources and had high feeding niche overlap. Also, forest structure related to the spatial distribution of main food sources did not explain spatial segregation because parts used by each species exclusively did not differ in density of trees, dead wood and lianas. We propose that life history trade-offs that result in species aggregation and a relative increase in the strength of intra-specific over inter-specific competition best explain the observed pattern of co-occurrence of ecologically similar congeneric Microcebus species.     

Habitat Use and Trophic Niche Overlap of Two Sympatric Colobines, Presbytis potenziani and Simias concolor, on Siberut Island, Indonesia

According to ecological theory, the concept of niche differentiation is essential to our understanding of how sympatric species can limit competition over resources. We here examine ecological niche differentiation in 2 sympatric Asian langurs, Presbytis potenziani and Simias concolor, both endemic to the Mentawai Islands off the west coast of Sumatra. We collected data (home range size, canopy use, activity budgets, diet, and niche breadth and overlap) using GPS and scan/focal animal sampling methods on 2 groups of Presbytis potenziani and 3 groups of Simias concolor living in a mixed primary rain forest in northern Siberut. Results show that home ranges of the 2 species overlapped completely and that the home range size of Presbytis potenziani was ca. 4 times larger than that of Simias concolor. Lower canopy levels (<20 m) were used more often by Simias concolor, whereas Presbytis potenziani preferred the canopy >20 m. Apart from foraging and other activities, there was little difference in overall activity budgets of the 2 species. Regarding diet, although 60% of all food species examined were used by both langur species, they shared only 3 of the 10 most commonly eaten species. Presbytis potenziani fed more selectively on fruits, whereas Simias concolor fed predominantly on leaves. Levin’s niche breadth indices revealed that the diet of Simias concolor is more general (0.34) than that of Presbytis potenziani (0.22). Based on a Pianka index of 0.32, we conclude that there is a relatively small food niche overlap between the 2 colobine species and that diet represents an important mechanism enabling their coexistence.     

Niche partitioning among three montane ground‐dwelling pheasant species along multiple ecological dimensions

Pheasants (order Galliformes) are typical ground‐dwelling birds, having a large body size and weak flight abilities. Sympatric pheasants are expected to share narrower niche space and face more extensive interspecific competition. However, little work has been undertaken simultaneously to investigate niche partitioning among sympatric pheasant species across multiple ecological dimensions. We compared microhabitat use, activity pattern and foraging strategy of sympatric Blood Pheasant Ithaginis cruentus, Buff‐throated Partridge Tetraophasis szechenyii and White Eared‐pheasant Crossoptilon crossoptilon on the Qinghai‐Tibet Plateau, China, to identify potential interspecific niche partitioning along different ecological dimensions in the breeding season. We found that the Buff‐throated Partridge differed significantly from the other two species in microhabitat use, and the three species showed different foraging strategies. It is likely that niche partitioning reduced potential interspecific competition, thus facilitating the species’ stable coexistence. Our study provides practical evidence of multidimensional niche theory within sympatric ground‐dwelling pheasant species, emphasizing that species interactions and coexistence within a guild are often not uni‐dimensional. Given global conservation concern for maintaining bird diversity, we recommend further restriction of yak grazing in these species’ habitat.     

Prey foraging of red titi monkeys, Callicebus cupreus, in comparison to sympatric tamarins, Saguinus mystax and Saguinus fuscicollis

We compared the prey capture strategies of red titi monkeys, Callicebus cupreus, with those of sympatric mustached, Saguinus mystax, and saddleback tamarins, Saguinus fuscicollis, to examine whether animal prey is important in niche differentiation between these Neotropical primates. We collected data on strata and substrate use during foraging, on prey searching and capturing, and on prey type of two C. cupreus groups and one group each of S. mystax and S. fuscicollis during a 5-month field study in northeastern Peruvian Amazonia. Our results showed that C. cupreus differed both from S. mystax and S. fuscicollis in prey capture strategies: (1) C. cupreus used lower forest strata for prey search and capture than S. mystax and higher forest strata than S. fuscicollis. (2) C. cupreus captured prey on a higher variety of substrates than S. mystax and more often on open microhabitats compared to S. fuscicollis. (3) C. cupreus captured prey more often directly than S. mystax and rarely by manual search, in contrast to S. fuscicollis. (4) C. cupreus fed exclusively on arthropods and focused on Hymenoptera, in contrast to both tamarin species that focused on Orthoptera and included vertebrates in their diet. These findings indicate that animal prey plays a role in niche differentiation between C. cupreus and S. fuscicollis/S. mystax and might facilitate the coexistence of these three sympatric species.