Biting the hand that feeds: the invasive grass Schismus barbatus (Poaceae) is facilitated by,but reduces establishment of,the native shrub Ambrosia dumosa (Asteraceae)

Question: We present a study of positive and negative interactions between the invasive grass Schismus barbatus (Poaceae) and Ambrosia dumosa (Asteraceae). Ambrosia facilitates seedling establishment, and such facilitation may accelerate invasion of exotic species, which, in turn, may reduce establishment of native plants. Location: Joshua Tree National Park, California, USA. Methods: During 2003‐2004, we used field surveys to characterize the natural spatial distribution of Schismus in relation to native shrubs, and experimentally manipulated seed rain of Ambrosia and Schismus at three distances from adult Ambrosia canopies. We measured percentage germination and individual performance of both species. Field data were complemented by a greenhouse experiment that measured competition between Ambrosia seedlings and Schismus planted at three densities and five relative abundances under controlled conditions. Results: Field surveys showed that the density of Schismus is independent of Ambrosia shrubs, but growth is enhanced near shrub canopies. In our field experiment Schismus is facilitated by adult Ambrosia. Under controlled conditions, Schismus does not respond to the density of Ambrosia seedlings, but changes in density of Schismus decreased performance of Ambrosia seedlings. Conclusion: Schismus invasion may be detrimental to native perennial plant populations. Although a reduction of seedling establishment is not usually expected to slow population growth of long‐lived perennials, recent unprecedented adult mortality in this community, and the well‐documented facilitative role of Ambrosia, suggest that Schismus invasion may be of high ecological significance.     

Pattern and mortality in Colorado Desert plants

Summary We tested for intraspecific interference among Colorado Desert shrubs using an integrated analysis of spatial pattern and juvenile mortality. The data set included 7,000 woody perennials of 24 species in a mapped hectare of Joshua Tree National Monument, California. The site is dominated by Ambrosia dumosa (62.0% of the stems), with Larre tridentata a conspicuous secondary species (2.3% of the stems). Analyses of static pattern for common species showed: (1) aggregated adults and juveniles for Ambrosia dumosa, Erigonum fasciculatum, Mirabilis bigelovii, and Sphaeralcea ambigua, with more aggregation among juveniles than adults; (2) randomly distributed adults and juveniles for Krameria grayi, Opuntia rasmosissima, Simondsia chinensis, and Yucca schidigera. The summed volumes and distances between nearest conspecific neighbors were positively correlated for Ambrosia dumosa and Larrea tridentata, but not significantly correlated for eight remaining species with 100 individuals. Static pattern suggests only weak evidence for negative interactions in Ambrosia and Larrea, and little evidence for other species. Alternative mechanisms other than negative interaction that could give rise to these static patterns are discussed. Juvenile mortality was documented for four common species (Ambrosia dumosa, Eriogonum fasciculatum, Mirabilis bigelovii, and Sphaeralcea ambigua) that experienced substantial mortality. Analyses show: (1) the proportion of individuals that died was independent of the initial density of conspecifics; (2) distance to conspecific adults did not differ for juveniles that died versus those that survived; and (3) death was no more likely for juveniles that contacted other plants than for those that were isolated. The exception was a vine, Mirabilis bigelovii, whose juveniles survived better in contact with other plants. In sum, neither spatial pattern nor patterns of mortality showed clear evidence of negative intraspecific interference.     

Adult plants facilitate their conspecific seedlings by enhancing arbuscular mycorrhizae in a saline soil

Aims

We tested the hypothesis that adult plants can help their conspecific (i.e. an organism belonging to the same species as another organism) seedlings develop symbiosis with arbuscular mycorrhizal fungi (AMF), thereby increasing seedling nutrient uptake and growth in a saline soil.

Methods

Using the halophytic shrub Tamarix chinensis as a model plant, we conducted two field experiments and a greenhouse experiment. Field experiment 1 assessed the importance of below-ground effects of adult neighbor. Field experiment 2 determined the involvement of AMF in neighbor effects by applying fungicide benomyl to obtain AMF suppressed treatment. The greenhouse experiment tested whether neighbor effects were influenced by AMF hyphal connection between adults and seedlings by using 25 μm and 0.45 μm nylon mesh to allow and prevent the AMF hyphae pass through respectively.

Results

Adult neighbor increased shoot biomass and nutrient of target seedlings and the below-ground effects mediated by AMF was facilitative under high soil salinity level. Field experiment 1 showed that adult neighbors reduced soil salinity, increased soil organic matter, and provided AMF spores for target seedlings via whole plant effects or below-ground effects alone. Field experiment 2 showed that shoot biomass and AMF colonization of target seedlings were greater with an adult neighbor when AMF were not suppressed treatment than in AMF were suppressed or there were no neighbors. In the greenhouse experiment, adult neighbors with AMF hyphal connection increased shoot biomass, AMF colonization, and ¹⁵N content of target seedlings under the high salinity level.

Conclusion

The results support our hypothesis that adult plants can promote the growth and nutrient uptake of their conspecific seedlings in a saline soil by helping them to develop AMF symbiosis. These findings highlight the roles of adult neighbor plants on seedlings regeneration through rhizospheric symbiosis in stressful environments.

     

Photosynthetic responses of tree seedlings in grass and under shrubs in early-successional tropical old fields, Costa Rica

Only recently have studies addressed the effect of early-colonizing vegetation on tree seedling survival and growth during secondary succession in tropical old fields, and few studies have elucidated the physiological responses of tree seedlings to different vegetational communities. We compared growth and various photosynthetic parameters for seedlings of four rain-forest tree species, Cedrela tonduzii, Inga punctata, Ocotea whitei, and Tapirira mexicana, growing in areas of pasture grass and shrubs in early-successional abandoned pasture in Costa Rica; in addition, we made measurements for two species in forest gaps. We tested the general hypothesis that early-colonizing shrubs facilitate growth of forest tree seedlings. Specifically, we measured microclimate, growth, CO₂ assimilation, stomatal conductance, photosystem II quantum yield (KPSII), and xanthophyll pigment pools for all seedlings. Photosynthetic flux density (PFD) was higher under grass than shrubs or forest gaps, but was highly variable in each growth environment. For three of the four species, height growth was greatest in the grass compared to the shrubs and forest gaps; growth was similar below grass and shrubs for O. whitei. Photosynthetic capacity, apparent quantum yield, and stomatal conductance did not vary across habitats, but light compensation point and PFD at light saturation tended to be higher in the grass compared to forest and shrub growth environments. Water use efficiency differed across growth environments for three of the species. For plants in ambient PFD and dark-adapted plants, the efficiency of excitation energy transfer through PSII was lowest for plants in the grass compared to shrubs and forest gaps and also differed across species. Measurement of steady-state responses of KPSII to increasing PFD indicated a significant effect of growth environment at low PFD for all species and significant effects at high PFD only for I. punctata. All species exhibited a high degree of midday xanthophyll de-epoxidation in the different growth environments. Xanthophyll pigment pool size on an area basis was highest in the grass compared to shrubs and forest gaps for all four species. The results suggest that shrubs do not provide a facilitative effect for growth or photosynthesis for ~1.5-year-old seedlings of these four species. We conclude that site differences in success of tree seedlings during succession are a result of complex interactions of facilitation and competition and are not simply based on physiological responses to PFD.     

Intraspecific competitive effects on water relations,growth and reproduction in Encelia farinosa

Summary An experiment was conducted to assess the importance of intraspecific competition on water relations, growth and reproductive output in Encelia farinosa, a common deciduous-leaved shrub of the Sonoran Desert. Nearest neighbor analyses in monospecific stands indicated that plants exhibited a clumped distribution. Plant size and nearest neighbor distance were positively correlated, inferring intraspecific competition. Removal experiments monitored for two years indicated that plants now without neighbors had higher leaf water potentials, higher leaf conductances, and a greater leaf area than control plants. As a consequence, growth rates and reproductive output were significantly higher in plants without neighbors. These data strongly support the notion that warm desert plants with a contagious spatial distribution compete for water.     

Density‐dependent Survival in Seedlings Differs among Woody Life‐forms in Tropical Wet Forests of a Caribbean Island

Negative density dependence contributes to seedling dynamics in forested ecosystems, but the relative importance of this factor for different woody plant life‐forms is not well‐understood. We used 1 yr of seedling survivorship data for woody seedlings in 17 different plots of lower to mid‐montane rain forests on the island of Dominica to examine how seedling height, abiotic factors, and biotic factors such as negative density dependence are related to seedling survival of five different life‐forms (canopy, midstory, and understory trees; shrubs; and lianas). Across 64 species, taller seedlings in seedling plots with higher canopy openness, greater seedling density, lower relative abundance of conspecific seedlings, and lower relative abundance of conspecific adults generally had a greater probability of surviving. Height was the strongest predictor of seedling survival for all life‐forms except lianas. Greater seedling density was positively related to survival for canopy and midstory trees but negatively related to survival for the other life‐forms. For trees, the relative abundance of conspecific seedling and adult neighbors had weak and strong negative effects on survival respectively. Neither shrub nor liana seedling survival was affected by the relative abundance of conspecific neighbors. Thus, negative density dependence is confirmed as an important structuring mechanism for tree seedling communities but does not seem to be important for lianas and shrubs in Dominican rain forests. These results represent the first direct assessment of controls on seedling survival of all woody life‐forms – an important step in understanding the dynamics and structure of the entire woody plant community.     

The effects of interspecific interactions on resource use and behavior in a desert ant

We examined how interspecific competition in ants affects resource use and behavior. To test how neighboring Myrmecocystus colonies influence the desert ant Aphaenogaster cockerelli, we placed temporary enclosures around Myrmecocystus spp. colonies and recorded the resources collected by A. cockerelli and the numbers of A. cockerelli ants engaged in various tasks outside the nest. When neighbors were enclosed, A. cockerelli colonies collected a significantly higher proportion of termites and significantly less plant matter than when neighbors were active. The numbers of A. cockerelli ants engaged in foraging behavior and nest maintenance work increased when Myrmecocystus colonies were enclosed. Interspecific interactions thus can affect the behavior and resource use of A. cockerelli colonies and may influence colony fitness.     

Rosa multiflora’s performance under water stress: the role of positive and negative density-dependent intraspecific interactions

It is well known that biotic interactions may significantly alter plant population and community dynamics in natural ecosystems. Multiple studies have reported that density-dependent positive interactions can modify the effect of extreme stress on plant performance (in line with predictions by the stress gradient hypothesis, SGH). However, the performance of invasive species and the role of intraspecific density dependence, either negative or positive, in successful invasions are not well understood. In the present study, we tested if monocultures of Rosa multiflora, a highly invasive shrub, experience a group advantage under extremely low water availability. Using a manipulative greenhouse study, we tested the growth response of R. multiflora seedlings to a 4-level conspecific density treatment and a 4-level water availability gradient. Overall, our results provide preliminary evidence that biotic interactions under stressful conditions between R. multiflora individuals do not experience a group advantage, as predicted. Instead, our study indicates that seedling performance was strongly driven by negative density dependence, in which individuals grown at higher conspecific densities displayed lower plant performance, regardless of water availability. This demonstrates that R. multiflora experiences intense intraspecific competition even under a stressful, low resource environment. Thus, management efforts of R. multiflora need to ensure that re-sprouting of individuals after treatment is eliminated, as release from negative density dependence could lead the invader population to rebound.

     

Direct and indirect interactions among plants explain counterintuitive positive drought effects on an eastern Mediterranean shrub species

Coexistence of woody and herbaceous plants may be governed by a complex set of direct and indirect interactions, whose relative importance have been rarely assessed. We experimentally studied woody species establishment in a mixed plant community by disentangling the potential role of such biotic interactions and the effect of environmental variations on them. Seedling establishment of the common eastern Mediterranean shrub species Sarcopoterium spinosum was investigated under different rainfall and light conditions, combined with the effect of the presence of adult shrubs and annual neighbors. We predicted that seedlings will be directly affected by competition with annuals with increasing water availability, while direct effects of adult shrubs will be positive via amelioration of water stress. Indirect effects were expected beneath shrub canopies due to reduced water stressed and light availability for both annuals and shrub seedlings, which may intensify competition between annuals and shrub seedlings. To test these predictions we performed field and garden experiments in which we combined manipulation of shrub and annual presence with manipulations of water availability and light conditions to simulate the effect of shrub canopy. In contrast to our prediction, shrub seedling establishment was not facilitated but inhibited by adult shrubs because of light limitation. As expected, annuals had direct negative effects on shrub seedlings under wet conditions, which shifted to neutral or positive effects under dry conditions. Thus, interactions among shrubs and annuals, and in particular the release from competition during drought years, leads to a counterintuitive positive effect of drought on shrub seedling establishment. Our findings point to the importance of experimentally studying multidimensional interactions for coexistence of different life forms and to the underestimated role of light for success in water‐limited ecosystems.     

The fitness benefits of germinating later than neighbors

Premise of the Study

Phenology, the seasonal timing of development, can alter biotic interactions. Emergence from dormant or quiescent stages often occurs earlier when neighbors are present, which may reduce the neighbors' competitive effects. Delayed emergence in response to neighbors also has been observed, but the potential benefits of such delays are unclear. Further, emergence time may respond to neighbors experienced by parents, which may predict future competition in offspring.

Methods

In the annual plant Arabidopsis thaliana (Brassicaceae), we quantified seed germination responses to neighbors in parental and offspring (seed) environments. To examine how observed changes in germination affect interactions with neighbors, we performed an outdoor experiment using neighbors of different sizes to represent different germination times.

Key Results

Seeds were more likely to germinate if their parent had neighbors, but they were less likely to germinate if they themselves experienced a neighbor cue (canopy). As seeds lost dormancy over time, they gained the ability to germinate under a canopy, which suggests that they germinate later in the presence of neighbors. Neighbors of both sizes reduced growth, survival to reproduction, fecundity, and total fitness, but large neighbors increased seedling survival. Smaller neighbors provided no such benefit and had stronger negative effects.

Conclusions

Delayed germination in response to neighbors can reduce negative interactions and promote positive ones if it occurs late enough to expose seedlings to larger neighbors. By altering relative phenologies and, in turn, the outcomes of biotic interactions, phenological responses to environmental change may influence species interactions and community dynamics.     

Intraspecific variation in fruit–frugivore interactions: effects of fruiting neighborhood and consequences for seed dispersal

The extent of specialization/generalization continuum in fruit–frugivore interactions at the individual level remains poorly explored. Here, we investigated the interactions between the Neotropical treelet Miconia irwinii (Melastomataceae) and its avian seed dispersers in Brazilian campo rupestre. We built an individual-based network to derive plant degree of interaction specialization regarding disperser species. Then, we explored how intraspecific variation in interaction niche breadth relates to fruit availability on individual plants in varying densities of fruiting conspecific neighbors, and how these factors affect the quantity of viable seeds dispersed. We predicted broader interaction niche breadths for individuals with larger fruit crops in denser fruiting neighborhoods. The downscaled network included nine bird species and 15 plants, which varied nearly five-fold in their degree of interaction specialization. We found positive effects of crop size on visitation and fruit removal rates, but not on degree of interaction specialization. Conversely, we found that an increase in the density of conspecific fruiting neighbors both increased visitation rate and reduced plant degree of interaction specialization. We suggest that tracking fruit-rich patches by avian frugivore species is the main driver of density-dependent intraspecific variation in plants’ interaction niche breadth. Our study shed some light on the overlooked fitness consequences of intraspecific variation in interaction niches by showing that individuals along the specialization/generalization continuum may have their seed dispersed with similar effectiveness. Our study exemplifies how individual-based networks linking plants to frugivore species that differ in their seed dispersal effectiveness can advance our understanding of intraspecific variation in the outcomes of fruit–frugivore interactions.

     

八大公山常绿落叶阔叶混交林影响幼苗存活的主要因子分析

幼苗是植物生活史中最脆弱的阶段,对幼苗存活影响因子的分析有助于我们更清楚的了解森林群落的天然更新机制。利用广义线性混合模型（GLMM）对八大公山常绿落叶阔叶混交林中影响幼苗存活的主要生物与非生物因子进行了研究。结果表明：（1）在群落水平上,幼苗存活与生物因子中的同种幼苗密度呈显著负相关,与非生物因子中的冠层开阔度呈显著正相关;（2）从年龄上看,4年生以下龄级的幼苗存活更容易受到同种幼苗密度的影响,与同种幼苗密度呈显著负相关;4年生及其以上的幼苗存活则主要受非生物因子影响;（3）从生活型上看,相对于常绿物种,落叶物种的幼苗存活率更容易受到同种幼苗密度的影响,也与冠层开阔度呈正相关;（4）在物种水平上,生物因子与非生物因子对不同物种幼苗存活率的影响也不相同。其中,宜昌润楠（Machilus ichangensis Rehd.et Wils.）的存活率与冠层开阔度呈正相关;薄叶山矾（Symplocos anomala Brand）幼苗的存活率与同种幼苗密度、异种大树胸高断面积、林冠开阔度、坡向均呈显著负相关,而与异种幼苗密度和海拔呈显著正相关。本研究表明影响幼苗存活的因子是多样的,而且不是随机发生的。在不同水平上影响幼苗存活的因子不同。     

Zonation of shrubs in western Atlantic salt marshes

We explored the generality of the processes mediating shrub zonation in western Atlantic salt marshes by comparing the results of our experiments in Georgia, USA with previous studies from Rhode Island, USA. The shrub Borrichia frutescens dominates the terrestrial border of many Georgia salt marshes. Within the shrub zone, physical stress increased at lower elevations, shrubs at lower elevations were stunted, and experimentally reducing physical stress reduced shrub stunting. Below the shrub zone, physical stress increased further, and the grass Spartina alterniflora dominated. Transplant and neighbor-removal experiments indicated that the lower border of the shrub zone was set more by physical stress than by competition, but that the upper border of the grass zone was set primarily by competition with shrubs. Laboratory experiments indicated that S. alterniflora seedlings survived best and shrub seedlings worst in the flooded, salty treatment that mimicked low-marsh conditions. These processes are similar to those maintaining zonation patterns between the shrub Iva frutescens and the rush Juncus gerardi in Rhode Island salt marshes. However, markedly different processes appear to occur further to the north, where woody shrubs are absent from coastal marshes, and further to the south, where woody plants (mangroves) dominate coastal wetlands.     

Mediation of growth by conspecific neighbors and the effect of site in transplanted fragments of the coral Porites attenuata Nemenzo in the central Philippines

To investigate facilitative and competitive effects of conspecific neighbors on coral growth, fragments of Porites attenuata were reciprocally transplanted between two reefs. Transplants were interspersed with dead coral fragments or live conspecifics and monitored for growth. Over 13 months, transplant performance differed between sites. Those from degraded Bais Bay grew significantly slower in all treatments compared with those from more pristine Apo Island, and Bais fragments branched less (Bais: 1.5ǂ.16/transplant; Apo: 8.1ǂ.66/transplant). Treatment effects were observed in Apo; fragments with live conspecifics branched less but grew taller, adding significantly more surface area than those with dead neighbors. Clonal fragments differed significantly in their responses, indicating environmentally induced effects. These interactions affected growth and morphology prior to physical contact between fragments. This illustrates a benefit of manipulating the biotic environment of early transplants: dense stocking in ocean nurseries could stimulate early growth, and subsequent spacing would allow lateral branching and reduce competition.     

Effect of soil nutrients,neighbor identities and root separation types on intra‐ and interspecific interaction among three clonal plant species

In natural environments, plants frequently interact with both heterospecific and conspecific neighbors. The intensity of belowground plant interaction with neighboring species commonly varies with the availability of soil nutrients in the habitats. According to classical ecological theory, competition between conspecific neighbors may be more severe than competition between unrelated species due to the similar nutrient requirements of close relatives, especially when nutrients are scarce in the habitat. However, many recent studies have shown the opposite pattern, and suggested an alternative mechanism based on species recognition. Taking Zoysia sinica as the focal species, we conducted a controlled experiment to test the results of intraspecific and interspecific interactions among three clonal species Zoysia sinica, Zoysia japonica and Alternanthera philoxeroides, which represent a conspecific, a close relative and a distant relative of the focal species, respectively, and at different root treatments (no separation NS, clone separation CS and ramet separation RS) and two nutrient levels. The results showed that Z. sinica recognized conspecific plants in the NS and CS treatments, and did not show above or belowground competition with these. The performance of the focal plant (Z. sinica) was better when it was grown with a conspecific neighbor as compared to all other types of neighbors. In all root separation treatments, the competition was more intense when Z. sinica grew with a close relative (Z. japonica) than when growing with a distant relative (A. philoxeroides). Generally, competition between plants was more intense at the high nutrient level than at the low nutrient level, suggesting that both soil nutrients and a species recognition mechanism play a significant role for the intra‐ and interspecific interaction and fitness of these three neighboring clonal species.     

How recruitment, intraspecific interactions, and predation control species borders in a tidal estuary

We examined the relative contribution of recruitment, intraspecific species interactions, and predation in controlling the upper intertidal border of the northern acorn barnacle, Semibalanusbalanoides, in a tidal estuary in Maine. We hypothesized that the contracted border at sites that experienced low tidal currents was due to flow-mediated recruitment that resulted in reduced survival due to the absence of neighbor buffering of thermal stress (i.e., positive intraspecific interactions). We tested this hypothesis by manipulating the density of recently settled barnacles and their thermal environment in a field experiment. Counter to our original hypothesis, barnacles with neighbors suffered severe mortality at low-flow sites. When density-dependent predation by the green crab (Carcinusmaenus) was experimentally eliminated, however, we did detect evidence for positive interactions at the low-flow sites but not at the high-flow sites. In spite of the close proximity of the sites, maximum daily rock temperatures at the low-flow sites were slightly, but consistently, greater than those at high-flow sites. Our findings suggest that the upper intertidal border of S. balanoides in the Damariscotta River is limited at low-flow sites by a combination of reduced recruitment, elevated mortality from thermal stress and enhanced predation by green crabs. More generally, our findings highlight how physical stress and predation interact to alter the nature of density-dependent species interactions in natural assemblages. Received: 6 August 1998 / Accepted: 11 October 1998     

Indirect effects in a desert plant community: is competition among annuals more intense under shrub canopies?

An unresolved discussion in contemporary ecology deals with the relative importance of competition along environmental gradients. In deserts, local-scale differences in environmental productivity may be caused by the presence of shrubs, which represent a favorable habitat for annual populations within a nutrient-poor matrix. In this study, we attempted to test the hypothesis that facilitation of desert annuals by shrubs increase the intensity of competition among the annual plants. Such negative indirect effects have so far been ignored in studies about plant-plant interactions. We tested our hypothesis by measuring seedling survival and fecundity of four abundant annual plant species with and without neighbors in open areas and under shrub canopies in a sandy desert area. Our findings did not indicate indirect negative effects of shrubs on their understory annuals. Sensitivity to the presence of neighbors varied between species and surprisingly, the species with the smallest seeds was the only one which was not negatively affected by the presence of neighbors. In contrast to our hypothesis, there was no difference between the habitat types shrubs and openings in absolute and relative competition intensity. Our overall results suggest that negative indirect effects of shrubs are unimportant in determining demographic response of understory annual plants.     

不同性别邻体和土壤灭菌对青杨幼苗生物量的影响

尽管植物邻体关系受到广泛关注,但关于雌雄异株植物性别间邻体关系的研究还较少.本研究比较了雌、雄青杨幼苗生物量的积累对其邻株性别和土壤灭菌的响应差异,并分析了性别间的邻体效应关系及不同性别混栽下生物量的差异.结果表明:同性邻株模式降低了青杨雌株或雄株生物量的积累,而异性邻株模式在未灭菌条件下促进了雌株的生物量积累;土壤灭...     

Positive interactions under nurse-plants: spatial scale, stress gradients and benefactor size

Positive interactions often play an important role in structuring plant communities and increasing biological diversity. Using three scales of resolution, we examine the importance of a long-lived desert tree, ironwood (Olneya tesota), in structuring plant communities and promoting biological diversity in the Sonoran Desert. We examined the positive effects of Olneya canopies of different sizes on plant communities in mesic and xeric habitats throughout the central Gulf Coast subregion of Sonora, Mexico. In xeric sites, Olneya canopies had strong positive effects on plant richness and abundance, and small positive effects on the size of plants, underscoring the role of facilitation in extreme environments. In mesic sites, Olneya canopies had very little effect on perennials and a negative effect on ephemeral richness, suggesting predominantly competitive effects in this less stressful environment. Overall, Olneya canopies increased biological diversity where abiotic stress was high, but did not increase diversity in more mesic areas. Thus Olneya canopies caused consistent shifts in plant-community structure among xeric and mesic sites, but not when these landscapes were combined. Benefactor size also mediated positive interactions, with larger Olneya canopies supporting larger perennials in both xeric and mesic sites. Thus stress gradients and benefactor size both influenced the balance of facilitative and competitive effects under nurse-plant canopies, and the spatial scale at which facilitative effects shape community structure.     

Olfactory Communication and Neighbor Recognition in Giant Kangaroo Rats

We hypothesized that olfactory communication facilitates neighbor recognition in the giant kangaroo rat, Dipodomys ingens , and is therefore influential in coordinating social interactions in this solitary, desert rodent. We tested whether (i) D. ingens can discriminate between odors of same- and opposite-sex conspecifics; and (ii) the kangaroo rats exhibit scent preferences based on familiarity. In habituation-discrimination tests, we found that both genders distinguish differences between the scent of individuals of the same- and opposite-sex. In olfactory preference tests, both males and females spent significantly more time investigating the scent of their familiar cagemate than the scent of an unfamiliar conspecific. Giant kangaroo rats may be able to recognize familiar neighbors from olfactory cues, thus supporting a hypothesis of neighbor recognition. Neighbor recognition may be an important mechanism of social interactions in this endangered species.