Resumen Las hormigas son sensibles a cambios ambientales y la estructura de la comunidad puede ser moldeada por la heterogeneidad ambiental y las interacciones interespecíficas. Probamos 2 hipótesis: (1) la estructura de la vegetación afecta negativamente la diversidad de hormigas en hábitats simplificados y (2) las interacciones interespecíficas dan forma a las comunidades de hormigas. Colectamos hormigas en arbustos de 16 unidades de muestreo de 100 m2 utilizando paraguas entomológicos y bateo en un área en regeneración de Cerrado, Brasil. La riqueza, abundancia y altura promedio de plantas se utilizaron como medida de heterogeneidad ambiental. Muestreamos 457 hormigas de 17 especies. Observamos una mayor riqueza de especies en parcelas con mayor abundancia de plantas y menor altura, y una relación negativa entre la abundancia y la altura de plantas. Corroboramos que la estructura de la vegetación afecta negativamente la diversidad de hormigas en hábitats simplificados. Los valores observados del índice de coexistencia difirieron de lo esperado en matrices simuladas, sugiriendo que la competencia moldea la comunidad de hormigas en hábitats simplificados. Destacamos la importancia de conservar árboles pequeños en hábitats menos complejos, porque representan elementos clave que albergan una gran diversidad.

Abstract Ant species are highly sensitive to environmental changes, and ant community structure can be shaped by environmental heterogeneity and interspecific interactions. We tested 2 hypotheses: (1) vegetation structure negatively affecting ant diversity in simplified habitats and (2) interspecific interactions shaping ant communities. We collected ants on shrubs distributed in 16 sampling units of 100 m2 using the entomological umbrella and beating technique in a regenerating Cerrado area of Brazil. The richness, abundance and average height of the plants were used as a measure of environmental heterogeneity. A total of 457 ants belonging to 17 species were sampled. We observed higher ant species richness in plots with greater plant abundance and lower plant height. We observed a negative relationship between ant abundance and plant height per plot. These results corroborate that vegetation structure negatively affects ant diversity in simplified habitats. The observed values of co-occurrence index differed from the expected values of simulated matrices, suggesting that competition shaping ant community in simplified habitats. We highlight the importance of conserving small trees, especially in structurally less complex habitats, because they represent key elements that harbor high ant species diversity.

ABSTRACT Copaifera oblongifolia is a recurrent plant species in degraded areas yet there is little information about its seed biology and interactions with fungi. The aims of this study were to identify the fungal community (endophytic and non-endophytic) associated with C. oblongifolia seeds and to test the effects of these different fungal species on germination. In general, germination of C. oblongifolia seeds was high (about 85 %), initiating four days after sowing and continuing for a total of 20 days. External asepsis with sodium hypochlorite did not influence germinability of C. oblongifolia. Seed infestation with Aspergillus niger, A. flavus, Mucor sp. and Rhizopus stolonifer did not affect the time required for germination, however, infection with A. flavus negatively affected germination percentage. Endophytic fungi were not isolated from C. oblongifolia seeds, suggesting that this species does not transmit endophytic fungi vertically. Therefore, C. oblongifolia can be classified in Class 3 with regard to the transmission and presence of endophytes.

ResumenLas plantas tienen recursos limitados para invertir en reproducción, crecimiento vegetativo y defensa contra herbívoros. El cambio en la distribución de recursos promueve variaciones en rasgos vegetales, que pueden afectar los niveles tróficos superiores. Durante dos años consecutivos de alta y baja inversión reproductiva se evaluó el cambio de recursos entre crecimiento vegetativo y defensa, y su efecto indirecto sobre la herbivoría en Copaifera langsdorffii. Nos preguntamos: i) ¿La inversión de recursos para la reproducción causa reducción del crecimiento vegetativo, como predice la hipótesis de equilibrio carbono/nutrientes, haciendo posible gastar más recursos en defensa? ii) ¿La variación en distribución de recursos para crecimiento y defensa entre años de alta y baja fructificación modifica indirectamente la herbivoría? Se monitorearon treinta y cinco árboles durante 2008 (gran fructificación) y 2009 (sin fructificación) en un área de vegetación de cerrado (Brasil), para evaluar la inversión diferencial en rasgos vegetativos (biomasa, crecimiento y No. de ramificaciones), defensa (concentración de taninos e hipersensibilidad vegetal) y herbivoría. De acuerdo a nuestra primera pregunta, se observó que en el año de fructificación la biomasa leñosa afectó negativamente la concentración de taninos, indicando que la producción de frutos redujo los recursos que podían invertirse en crecimiento y defensa. Además, la resistencia de las plantas y el ataque de agallas fueron influidos positivamente por la concentración de taninos y la biomasa foliar, lo que sugiere que la resistencia de los árboles a la herbivoría es un buen indicador de defensa vegetal y una estrategia efectiva de defensa de C. langsdorffii, además hay evidencia de respuesta trófica indirecta, como se postula en la segunda pregunta. En resumen, el patrón de fructificación supra-anual provoca varios efectos en el desarrollo de las plantas, mostrando la importancia de evaluar diversos rasgos vegetales al caracterizar la inversión de recursos de una especie. Como se esperaba, el cambio en la distribución de recursos modifica la producción de compuestos de defensa y los patrones de herbivoría. El entendimiento de este elemento importante de las interacciones insecto-planta será fundamental para descifrar la historia natural coevolutiva y las interacciones entre reproducción vegetal y ataque herbívoro. Además de eso, solo a través de estudios a largo plazo vamos a ser capaces de construir modelos y desarrollar pronósticos más precisos acerca de los factores que desencadenan el efecto de abajo hacia arriba en el rendimiento de la herbivoría, así el efecto de arriba hacia abajo de los herbívoros sobre la evolución de las plantas.

AbstractPlants have limited resources to invest in reproduction, vegetative growth and defense against herbivorous. Trade-off in resources allocation promotes changes in plant traits that may affect higher trophic levels. In this study, we evaluated the trade-off effect between years of high and low fruiting on the investment of resources for growth and defense, and their indirect effects on herbivory in Copaifera langsdorffii. Our questions were: (i) does the resource investment on reproduction causes a depletion in vegetative growth as predicted by the Carbon/Nutrient Balance hypothesis (CNBH), resulting in more availability of resources to be allocated for defense?, (ii) does the variation in resource allocation for growth and defense between years of high and low fruiting leads to indirect changes in herbivory? Thirty-five trees located in a Cerrado area were monitored during 2008 (year of high fruiting) and 2009 (year of no fruiting) to evaluate the differential investment in vegetative traits (biomass, growth and number of ramifications), plant defense (tannin concentration and plant hypersensitivity) and herbivory (galling attack and folivory). According to our first question, we observed that in the fruiting year, woody biomass negatively affected tannin concentration, indicating that fruit production restricted the resources that could be invested both in growth as in defense. In the same way, we observed an inter-annual variation in herbivorous attack, and found that plants with higher leaf biomass and tannin concentration, experienced higher galling attack and hypersensitive reaction, regardless years. These findings suggested that plants’ resistance to herbivory is a good proxy of plant defense and an effective defense strategy for C. langsdorffii, besides the evidence of indirect responses of the third trophic level, as postulated by the second question. In summary, the supra-annual fruiting pattern promoted several changes on plant development, demonstrating the importance of evaluating different plant traits when characterizing the vegetative investment. As expected by theory, the trade-off in resource allocation favored changes in defense compounds production and patterns of herbivory. The understanding of this important element of insect-plant interactions will be fundamental to decipher coevolutionary life histories and interactions between plant species reproduction and herbivory. Besides that, only through long-term studies we will be able to build models and develop more accurate forecasts about the factors that trigger the bottom-up effect on herbivory performance, as well the top-down effect of herbivores on plant trait evolution. Rev. Biol. Trop. 64 (2): 507-520. Epub 2016 June 01.

Predação de Sementes de Copaifera langsdorffi Desf. (Fabaceae: Caesalpinioideae) por Rhinochenus brevicollis Chevrolat (Coleoptera: Curculionidae) em uma Área de Cerrado do Brasil: Insetos predadores de sementes geralmente são herbívoros especializados que podem ser afetados por características da planta hospedeira. Neste estudo, a predação das sementes de Copaifera langsdorffi por Rhynochenus brevicollis foi caracterizada testando-se as hipóteses da concentração do recurso e da arquitetura da planta. O estudo foi realizado em um fragmento de cerrado localizado no norte do estado de Minas Gerais, Brasil. A percentagem de sementes de C. langsdorffi predadas por R. brevicollis variou de 1 to 30% (média±DP, 9.31±6.41). O número de frutos por ramos afetou negativamente a percentagem de predação das sementes por R. brevicollis.A predação de sementes pelo besouro mostrou relação positiva com a circunferência do tronco das árvores, mas a altura das árvores não afetou o ataque do predador. Assim, nossos dados não apresentaram suporte real para as duas hipóteses testadas. Finalmente, o estudo discute o papel da frutifcação supra-anual na regulação da população de R. brevicollis.

Seed predator insects are generally highly specialized herbivores that can be affected by several plant characteristics. In this study, the resource concentration hypothesis and the plant architecture hypothesis were tested by evaluating the attack of Rhynochenus brevicollis on Copaifera langsdorffi seeds. The study was conducted in a cerrado fragment situated in southeastern Brazil. The percentage of C. langsdorffi seed predation by R. brevicollis ranged from 1 to 30% (mean±SD, 9.31±6.41). The percentage of seed predation was negatively related to the number of fruits per branch. The predation of seeds by the beetle was positively affected by plant crown circumference, while plant height did not show any relationship with seed predation. Thus, our results did not support any of the two hypotheses evaluated. Finally, the study discusses the role of plant phenology (masting) in regulating the seed predator's population in cerrado vegetation.

The plant population dynamic is affected by ecological and evolutionary processes that operate at all stages of the plant life cycle. The aim of this study was to characterize the seed and seedling performance of Copaifera langsdorffii by testing four hypotheses: the resource concentration hypothesis; the relationship between seed size and germinability hypothesis; the relationship between seed size and seedling vigor hypothesis; and the intraspecific seedling competition hypothesis. All seeds used in the experiments were collected from 35 C. langsdorffii plants located in a fragment of the Brazilian cerrado (savanna). The number of fruits per plant negatively affected Rhinochenus brevicollis attacks on C. langsdorffii seeds. Therefore, this result does not support the resource concentration hypothesis, and predator satiation was used in order to explain the observed result. In general, seed germinability (percentage and time to emergence) was not influenced by seed size. The homogeneity of the experimental design, together with an abundant water supply, may have masked the effects of seed size on germinability. Seed size positively affected seedling development, corroborating the expected relationship between seed size and seedling vigor. The number of seedling per plastic bags negatively affected the growth of C. langsdorffii. The nutrient-limited soil probably promoted the below-ground competition for nutrients among seedlings. Finally, the role of evolutionary and ecological factors on C. langsdorffii population dynamics is discussed.

La simplificación de los hábitats naturales conduce a una modificación de la comunidad asociada con una planta huésped. En la región central de Brasil es muy común encontrar árboles aislados de “pequi” (Caryocar brasiliense) en medio de monocultivos de soya, maíz, pastos o plantaciones de eucalipto. Bajo este escenario, nosotros predecimos que la modificación del hábitat afecta diferencialmente la diversidad de hormigas y herbívoros asociados a árboles de “pequi”. El objetivo de este artículo fue determinar que árboles de “pequi” localizados en hábitats modificados por actividades humanas (i.e. pastizales y plantaciones de Eucalyptus), soportan una menor abundancia y riqueza de especies de hormigas. Por el contrario, se espera una mayor abundancia y riqueza de especies de herbívoros en hábitats modificados. Este estudio fue realizado en un área de Cerrado (sabana brasileña) localizado en el Norte del estado de Minas Gerais, Brasil. Las hormigas y los herbívoros fueron muestreados usando técnicas de golpe. La riqueza de especies de hormigas fue mayor en árboles de “pequi” localizados en áreas preservadas de Cerrado, seguida por árboles de pastizales y finalmente por árboles de plantaciones de Eucalyptus. La abundancia de hormigas fue menor en plantaciones de Eucalyptus, pero no hubo diferencias en la abundancia de hormigas entre árboles de pastizales y áreas preservadas de cerrado. Por otra parte, el número de especies de insectos herbívoros fue menor en árboles de áreas preservadas de Cerrado que en pastizales y plantaciones de Eucalyptus. Concluimos que las actividades humanas reducen la complejidad del hábitat resultando en la pérdida de la diversidad de insectos y procesos ecológicos.

Simplification of natural habitats leads to a modification of the community associated with a host plant. Pequi trees (Caryocar brasiliense) are common to find in central Brazil, especially in the middle of monocultures, such as soy, corn, pasturelands or Eucalyptus plantations. On this scenario we hypothesized that habitat modification differentially affects the diversity of ants and herbivore insects associated with this species. The aim of the work was to test if C. brasiliense trees located in human modified habitats, support a lower species richness and abundance of ants, and a greater species richness and abundance of insect herbivores, compared to preserved cerrado habitats. The study was conducted in a Cerrado area located in Northern Minas Gerais State, Brazil. Ants and herbivore insects were collected monthly during 2005 using beating technique. The results showed that ant species richness was higher in pequi trees located in preserved Cerrado, followed by trees in pastureland and Eucalyptus plantation, respectively. The ant abundance was lower in the Eucalyptus plantation but no difference in ant abundance was observed between trees in pastureland and the preserved Cerrado. Moreover, herbivore insects exhibited lower number of species and individuals in trees located in the preserved Cerrado than in the pastureland and Eucalyptus plantation. We concluded that habitats simplified by human activities may result in diversity loss and may change species interactions.

Os frutos de Dimorphandra mollis são coletados de forma indiscriminada para fins comerciais, comprometendo a viabilidade das populações naturais. Este estudo teve como objetivo avaliar o efeito da qualidade do solo na germinação das sementes e no desenvolvimento de plântulas de D. mollis. Solos de três procedências (cerrado arenoso, cerrado argiloso e mata seca) foram usados como substratos nos testes de germinação e desenvolvimento das plântulas. As sementes de D. mollis apresentaram maior germinabilidade em solo de cerrado arenoso (60,5%), seguido por solo de cerrado argiloso (29,7%) e solo de mata seca (13,6%). Além disto, o índice de velocidade de germinação (IVG) das sementes de D. mollis foi maior no solo de cerrado arenoso. As raízes das plântulas cultivadas em solo de cerrado arenoso apresentaram maior comprimento do que as cultivadas nos solos de mata seca e cerrado argiloso. Contudo, a massa seca das raízes não variou entre os três tratamentos. As plântulas de D. mollis apresentaram maior crescimento e produção de biomassa da parte aérea quando cultivadas em solo de mata seca. Os solos das matas secas normalmente apresentam melhor qualidade nutricional que os solos do cerrado, justificando os resultados observados. Assim, para melhor sucesso da produção de mudas de D. mollis, as sementes devem ser germinadas em substratos que retêm pouca água e as plântulas devem ser cultivadas em solos de melhor qualidade nutricional.

The exploitative collection of Dimorphandra mollis fruits by farmers has negatively affected the natural population dynamics of this species. The aim of this study was to compare the effects of three soil types (Cerrado sand soil, Cerrado clay soil and dry forest soil) on seed germination and seedling development of D. mollis. The seeds of D. mollis showed greater germinability in Cerrado sand soil (60.5%), followed by Cerrado clay soil (29.7%) and dry forest soil (13.6%). The seedling root growth in Cerrado sand soil was higher compared to Cerrado clay soil and dry forest soil. However, no differences were verified for root dry mass between the soil treatments. The seedlings of D. mollis cultivated in dry forest soil presented a higher growth rate and total dry mass. These results are probably associated with higher nutrient availability, which was verified in the dry forest soil when compared to the Cerrado soils. Our results indicate that D. mollis seeds need a low water-retaining substrate to increase the germination rate and that seedlings develop better in nutrient-rich soils.

La hipótesis de heterogeneidad espacial se ha utilizado para explicar el aumento en la diversidad de especies desde los polos a los trópicos: los trópicos pueden ser más diversos ya que están conformados por una mayor cantidad de hábitats y micro-hábitats. En este estudio, la hipótesis de heterogeneidad espacial se puso a prueba evaluando la variación en la riqueza de dos gremios de insectos herbívoros (formadores de agallas y de alimentación libre) asociados con B. dracunculifolia (Asteracea) a lo largo de un gradiente latitudinal en Brasil. Las diecisiete poblaciones de B. dracunculifolia seleccionadas para el muestreo de insectos herbívoros estaban en hábitats con una estructura similar, a lo largo del límite Norte-Sur de distribución de la planta hospedera, cerca de la costa brasileña. De cada población de planta hospedera, se muestrearon treinta arbustos y se obtuvo un total de 8 201 agallas y 864 insectos de alimentación libre pertenecientes a 28 familias y 88 especies. La mayoría de los insectos que se encontraron en B. dracunculifolia estaban restringidos a un sitio específico en lugar de tener una distribución geográfica similar a la de la planta hospedera. La riqueza de especies de insectos de alimentación libre no se vió afectada por el gradiente latitudinal, por lo que se corroboró la hipótesis de heterogeneidad espacial. Mientras que la riqueza de especies de insectos formadores de agallas se correlacionó positivamente con la latitud, probablemente debido a que los insectos asociados al género Baccharis se extendieron hacia el sur de Brasil. Otros índices de diversidad y equidad estimados no variaron con la latitud para ninguno de los dos grupos de insectos herbívoros evaluados, lo que sugirie una estructura general para diferentes conjuntos de herbívoros asociados con la planta hospedera B. dracunculifolia. Por lo tanto, es probable que, la muestra de insectos en cada sitio sea resultado de eventos a gran escala, como la especiación, migración y coevolución; mientras que a nivel local la población de estos insectos está regulada por fuerzas ecológicas que operan dentro del sistema.

The spatial heterogeneity hypothesis has been invoked to explain the increase in species diversity from the poles to the tropics: the tropics may be more diverse because they contain more habitats and microhabitats. In this paper, the spatial heterogeneity hypothesis prediction was tested by evaluating the variation in richness of two guilds of insect herbivores (gall-formers and free-feeders) associated with Baccharis dracunculifolia (Asteraceae) along a latitudinal variation in Brazil. The seventeen populations of B. dracunculifolia selected for insect herbivores sampling were within structurally similar habitats, along the N-S distributional limit of the host plant, near the Brazilian sea coast. Thirty shrubs were surveyed in each host plant population. A total of 8 201 galls and 864 free-feeding insect herbivores belonging to 28 families and 88 species were sampled. The majority of the insects found on B. dracunculifolia were restricted to a specific site rather than having ageographic distribution mirroring that of the host plant. Species richness of free-feeding insects was not affected by latitudinal variation corroborating the spatial heterogeneity hypothesis. Species richness of gall-forming insects was positively correlated with latitude, probably because galling insect associated with Baccharris genus radiated in Southern Brazil. Other diversity indices and evenness estimated for both gall-forming and free feeding insect herbivores, did not change with latitude, suggesting a general structure for different assemblages of herbivores associated with the host plant B. dracunculifolia. Thus it is probable that, insect fauna sample in each site resulted of large scale events, as speciation, migration and coevolution, while at local level, the population of these insects is regulated by ecological forces which operate in the system. Rev. Biol. Trop. 59 (3): 1419-1432. Epub 2011 September 01.

O comportamento de induzir galhas provavelmente surgiu como um mecanismo de defesa contra adversidades climáticas e/ou refúgios contra inimigos naturais. Várias hipóteses foram propostas para explicar o padrão de distribuição e abundância desses herbívoros em suas plantas hospedeiras. Por exemplo, a hipótese da arquitetura da planta prediz que plantas arquiteturalmente mais complexas apresentam maior diversidade de herbívoros. Este estudo teve como objetivos avaliar o efeito da arquitetura da planta hospedeira na diversidade de galhas e determinar o esforço amostral mínimo para coleta representativa da fauna de galhadores em Copaifera langsdorffii. Cinquenta indivíduos arbóreos de C. langsdorffii foram selecionados para caracterização da arquitetura (altura, CAP, número de ramificações de primeiro, segundo e terceiro nível, área e volume da copa) e da riqueza e abundância de galhas. Um total de 23 morfotipos de galhas foi encontrado em C. langsdorffii. A curva de rarefação de espécies de galhas por indivíduo amostrado indicou que a saturação de espécies ocorre próxima a décima árvore amostrada. A complexidade arquitetônica não afetou a riqueza e abundância de galhas. Este estudo oferece uma nova metodologia para padronizar o método de amostragem de galhas em espécies arbóreas do Cerrado.

Plant architecture and gall diversity associated with Copaifera langsdorffii (Fabaceae). Galling insects induce tumors on their host plants in response to climatic adversities and as a protection against natural enemies. Among several hypotheses that explain differences in the distribution and abundance of galling-inducing insects, the plant architecture hypothesis stresses the influence of host plant architecture (e.g., a combination of life form, plant height, and number of shoots, branches and leaves in relation to crown volume). The aims of this study was to evaluate the effects of host plant architecture on gall species diversity and to determine the sample effort to perform a representative collect of the galling insects fauna. On fifty C. langsdorffii trees, we determined both architectural variables (i.e. height, DBH, number of ramifications of the first, second and third level, and crown area and plant volume) and gall richness and abundance. We found a total of 23 gall morphotypes associated with host plant C. langsdorffii. The gall richness and abundance were not affected by host plant architecture. Rarefaction curves indicated that ten individuals and 14 shoots per plant are sufficient to sample all gall morphotypes associated with C. langsdorffii. The study suggest a new methodology to sampling galls in this tropical tree species.

A riqueza e abundância de herbívoros associados a uma planta hospedeira são influenciadas por variações nas defesas físicas e químicas da planta as quais são mediadas pela qualidade do habitat. Neste estudo, 36 indivíduos de Copaifera langsdorffii distribuídos equitativamente entre habitats de Cerrado "sensu stricto", Matas Ciliares e Floresta Estacional Decidual foram usadas para avaliar os efeitos do habitat na esclerofilia foliar, produção de taninos e na fauna de insetos herbívoros associados. Observou-se maior riqueza e abundância de herbívoros mastigadores em plantas dos habitats de Mata Ciliar e Cerrado comparativamente à Floresta Estacional Decidual. Porém, a riqueza e abundância de insetos herbívoros sugadores não diferiu entre os habitats. Não foi encontrada relação entre a riqueza ou abundância de herbívoros com a concentração de taninos e a esclerofilia foliar de C. langsdorffii. Estas variáveis também não variaram entre os habitats. É provável que nesses ambientes a esclerofilia não esteja relacionada apenas com a herbivoria, e que alguns herbívoros podem não ser afetados negativamente ou beneficiados pela concentração de taninos encontrada. O lançamento de folhas por C. langsdorffi apenas no fim da estação seca na Floresta Decidual pode constituir um mecanismo de escape de herbivoria. Porém, para uma análise mais detalhada há necessidade de estudos a longo prazo sobre nos diversos tipos de ambientes nos quais esta espécies esta distribuída bem como da pressão exercida pelos seus herbívoros.

The richness and abundance of free-feeding insect herbivores may vary according to leaf sclerophylly, tannin concentration, and habitat conditions. We sampled 12 individuals of Copaifera langsdorffii in three different habitat physiognomies found in a cerrado-caatinga transition area in northern Minas Gerais, Brazil: 1) Cerrado ("sensu stricto"), 2) Riparian Forest, and 3) Seasonally Dry Forest (n=36 individuals). Higher richness and abundance of chewing herbivores were observed on C. langsdorffii in the Riparian Forest and Cerrado compared to Seasonally Dry Forest. On the other hand, the richness and abundance of sap-sucking herbivores did not differ among the habitats. No statistically significant differences were observed in leaf sclerophylly and tannin concentration among physiognomies, as well as no relationship was found among tannin concentration, leaf sclerophylly and richness and abundance of any of the insect guilds studied. The flushing of leaves by C. langsdorffi at the end of the dry season in the deciduous forest may be a mechanism to escape herbivores. Otherwise, for a detailed analysis long term studies at the vegetation formation where the host plant species is distributed and the selective pressures exerted by its herbivores are called for.

Myracrodruon urundeuva Allemão, espécie arbórea conhecida como aroeira, constitui-se em um importante componente das Florestas Estacionais Deciduais do norte de Minas Gerais. Apesar disso, a aroeira vem sofrendo um processo de exploração intensa, de forma predatória, o que vem causando a devastação de suas populações naturais. Este trabalho teve como objetivo conhecer os padrões fenológicos reprodutivos e vegetativos, bem como a capacidade germinativa da aroeira, na Área de Preservação da COPASA em Juramento, MG. Foram feitas observações fenológicas quinzenais, no período de janeiro/2002 a novembro/2003, de 20 indivíduos arbóreos, sendo ainda coletadas sementes, submetidas a diferentes tratamentos de escarificação tegumentar (mecânico, térmico, químico e controle). A espécie apresentou as fenofases reprodutivas e vegetativas influenciadas diferencialmente pelas variáveis ambientais de precipitação e temperatura. Na estação seca ocorreram a floração, frutificação e queda foliar, e a estação chuvosa favoreceu o brotamento da espécie. A capacidade germinativa dos diásporos de aroeira variou entre os tratamentos utilizados, com potencial germinativo e velocidade de germinação altos no tratamento-controle, indicando ausência de dormência. Nesse sentido, estudos básicos sobre as espécies florestais ameaçadas podem ser precursores de modelos e mecanismos para manejo e recuperação de suas populações naturais.

Myracrodruon urundeuva Allemão, an arboreal species known as aroeira, is an important component of seasonal dry forests in northern Minas Gerais. In spite of that, aroeira is experiencing a process of predatory exploitation, causing the devastation of its natural populations. This study aimed to assess the reproductive and vegetative phenological patterns, and the germinating capacity of the species. The study was carried out at the COPASA Preservation Area in Juramento (MG), where phenological phases were systematically observed bimonthly, from Janurary/2002 to November/2003 in 20 arboreal individuals. Seeds were collected and submitted to different scarification treatments (mechanic, thermal, chemical and control). The reproductive and vegetative phenophases of the species are influenced by environmental conditions. During the dry season, flowering, fructification and leaf fall occur, whereas the wet season favors leaf growth. Besides, the germination of aroeira seeds varied among treatments, with higher germinating potential and germination velocity being verified in the control treatment, indicating the absence of dormancy. Therefore, basic studies on the ecology of threatened forest species are essential to generate models and mechanisms for the management and restoration of their natural populations.

Os objetivos deste estudo foram caracterizar e comparar a composição florística de oito fragmentos de Mata Seca Calcária e Caatinga Arbórea localizados no norte do Estado de Minas Gerais. O levantamento das espécies arbóreas foi realizado através de visitas periódicas aos fragmentos para coleta de material botânico. Nos oito fragmentos foram encontradas 114 espécies arbóreas pertencentes a 40 famílias botânicas. Dentre as 89 espécies encontradas nos fragmentos de Mata Seca, 37 (42%) foram peculiares a essa formação. No entanto, das 75 espécies amostradas nos remanescentes de Caatinga Arbórea, 25 (33%) ocorreram apenas nesses fragmentos. A análise de agrupamento sugere que a composição florística dos fragmentos é afetada pela fitofisionomia e pelas condições bioecológicas locais a que estes fragmentos estão submetidos. Além disso, a relação observada entre a área dos fragmentos e o número de espécies arbóreas, evidenciou que área é um bom indicador da riqueza de espécies arbóreas nos fragmentos florestais. Portanto, os resultados deste estudo indicaram que fatores históricos (fitofisionomia) e ecológicos (área dos fragmentos e ocorrência de perturbações antrópicas) constituem importantes elementos caracterizadores da composição e riqueza de espécies em fragmentos florestais do norte de Minas Gerais.

The objective of this study was to characterize and compare the floristic composition of eight fragments of Calcareous Dry Forest and Arboreal Caatinga in the north of Minas Gerais State, Brazil. The survey of the tree species was performed by periodic visits to the fragments. We found 114 tree species belonging to 40 botanical families in the eight fragments. Of a total of 89 species found in the Calcareous Dry Forest fragments, 37 (42%) were typical of this formation. On the other hand, from the 75 species sampled in the Arboreal Caatinga remnants, 25 species (33%) occurred only in these fragments. The cluster analysis suggested that the floristic composition of the fragments was affected by the phytophysiognomy and by local bioecological conditions. The observed relationship between remnant area and tree species richness suggests that area was a good indicator of species richness in the forest fragments. The results of this study indicate that both historical (phytophysiognomy) and ecological (e.g., remnant area and occurrence of human disturbance) factors constitute important elements that determine the composition and richness of tree species of forest fragments in the north of Minas Gerais State.

Os efeitos de formigas na comunidade de insetos em inflorescências de Byrsonima crassifolia (Malpighiaceae) foram testados em um experimento de exclusão em uma vegetação de cerrado no Sudeste do Brasil. Quarenta e quatro espécies de insetos (23 famílias) e nove espécies de formigas (seis gêneros e três subfamílias) foram encontradas nas inflorescências de B. crassifolia. A exclusão das formigas, principalmente de Camponotus sericeiventris e de Camponotus spp. reduziu a população de membracídeos para 20% da abundância original. Exclusão das formigas e o tempo influenciaram a abundância de insetos mastigadores (exclusão, P<0,001; tempo, P<0,002) e sugadores (exclusão, P<0,02; tempo, P<0,01). Insetos mastigadores e sugadores foram encontrados duas vezes mais em inflorescências com formigas excluídas quando comparados com inflorescências controle (P<0,001). Insetos sugadores foram encontrados 1,5 vezes mais em inflorescências com formigas excluídas do que no controle. Apenas o tempo influenciou significativamente a riqueza de insetos mastigadores e sugadores associados com as inflorescências de B. crassifolia. Inflorescências em ramos controle foram significativamente menos atacadas por herbívoros do que inflorescências em ramos com formigas excluídas (P<0,001). Portanto, estes resultados sugerem que a presença das formigas influencia a estrutura da comunidade de insetos herbívoros associados com B. crassifolia.

The effects of ants on the insect community on inflorescences of Byrsonima crassifolia (Malpighiaceae) were tested in an ant exclusion experiment in a cerrado vegetation in southeastern Brazil. Forty-four species of insects (23 families) and nine species of ants (6 genera and 3 subfamilies) were found on the inflorescences of B. crassifolia. The exclusion of ants, primarily Camponotus sericeiventris and Camponotus spp., reduced the treehopper population to 20% of the original abundance. Ant exclusion and time influenced the abundance of chewing (Exclusion, P<0.001; Time, P<0.002), and sucking insects (Exclusion, P<0.02; Time, P<0.01). Twice as many chewing and sucking insects were found on ant-excluded inflorescences as compared to control inflorescences (P<0.001). One and half more sucking insects were found on ant-excluded than on control inflorescences. Only time significantly influenced the richness of chewing and sucking insects associated with B. crassifolia inflorescences. Inflorescences on control branches were significantly less attacked by herbivores than inflorescences on ant-excluded branches (P<0.001). Therefore, these results suggest that the presence of ants alters the structure of insect herbivore community associated with B. crassifolia.

A presente pesquisa objetivou avaliar os efeitos da taxa de crescimento de ramos na abundância dos insetos herbívoros de vida livre associados a Caryocar brasiliense em três diferentes "habitats" (cerrado, mata seca e pastagem). Em cada "habitat" foram escolhidas 20 árvores e em cada uma, marcados quatro ramos, que foram monitorados mensalmente de junho a novembro de 2001. Durante esse monitoramento foi encontrado um total de 47 morfoespécies de insetos (quatro ordens), associados aos ramos de C. brasiliense. A taxa de crescimento dos ramos foi significativamente diferente entre os "habitats" estudados. Contudo, apenas no cerrado se observou relação significativa entre a abundância de herbívoros e a taxa de crescimento dos ramos.

The present research aimed at evaluating the effects of branch growth rate in the abundance of free life herbivore insects associated with Caryocar brasiliense in three different habitats (savannah, dry forest, and pasture). In each habitat 20 trees were chosen and in each tree four branches were marked,they were monitored monthly from June to November of 2001. During the monitoring, 47 morphoespecies (four orders) were found associated with branches of C. brasiliense. Branch growth rate was significant by different, among the studied habitats. However, just in the savannah a significant relationship among the abundance of herbivores and branch growth rate was observed

Vellozia nivea (Velloziaceae) é planta de porte herbáceo que ocorre em solos rochosos, nos campos rupestres da Serra do Cipó, MG. Suas flores hermafroditas são extremamente macias, representando fonte tenra de alimento para os insetos que predam suas tépalas e estruturas reprodutivas. Este trabalho teve como objetivo observar a influência da altura e do número de flores da planta hospedeira na abundância e riqueza de insetos herbívoros. Foram encontradas o total de 21 morfoespécies de insetos (nove famílias e três ordens) associadas às flores de V. nivea. A altura e o número de flores da planta não apresentaram correlações significativas com a riqueza de herbívoros por planta (r² = 0,17; P > 0,05). Entretanto, estes dois fatores juntos explicaram 39% da variação observada na abundância dos insetos herbívoros por planta (P < 0,05). Portanto, o número de flores e a altura das plantas hospedeiras influenciaram apenas a abundância dos herbívoros.

Vellozia nivea (Velloziaceae) is a herbaceous plant that occurs on rocky soils in the rupestrian fields of the "Serra do Cipó", Minas Gerais State, Brazil. Its hermaphrodite flowers are extremely soft, representing a source of tender food for the insects that prey on its tepals and reproductive structures. The aim of this study was to observe the effect of the height and number of flowers of the host plant on the abundance and richness of herbivorous insects. We found 21 morphospecies of insects (nine families and three orders) associated to flowers of V. nivea. No significant correlation between the number of flowers and plant height and the variety of herbivorous insects per plant was observed (r² = 0.17, P > 0.05). However, these two factors together explained 39% of the variation of insect abundance (P < 0.05). Thus, only the abundance of herbivorous insects was influenced by the number of flowers and the height of host plant.