Demography of a Savanna Palm Tree: Predictions From Comprehensive Spatial Pattern Analyses

Abstract

Existing statistical methods for spatial pattern analysis now permit precise analyses of patterns and, given the appropriate interpretation keys, the formulation of testable hypotheses about the underlying processes. From a comprehensive analysis of the spatial pattern of a plant population and its environment, we infer scenarios of links between demographic processes, plant spatial patterns, and environmental heterogeneity. The palm tree Borassus aethiopum has easily identifiable demographic stages, a root foraging strategy enabling adults to reach distant nutrient sources, and a marked senescence starting with the onset of reproduction. We analyzed map data for palm individuals (in three different life history stages plus two sexes for adults) and for nutrient‐rich patches (clumps of other tree species and termite mounds) in three vegetation types (facies) of a humid savanna of West Africa (Lamto, Ivory Coast). Spatial analyses were based on Diggle’s nearest neighbor functions F and G and on Ripley’s K function. The main results were as follows: (1) juveniles and seedlings are aggregated, while adults have a random pattern or are more loosely aggregated; (2) all stages except female adults are spatially associated with nutrient‐rich patches, but association distances increase with stage in the life cycle; and (3) seedlings are associated with female adults, whereas the association of juveniles at longer distances is not clear‐cut. We propose from these results a parsimonious scenario linking spatial pattern and mortality pattern during the life cycle. The initial pattern of seedlings (close to maternal trees) results from low dispersal distance. Later stages (older seedlings and juveniles) are mostly restricted to nutrient‐rich patches through nutrient shortage away from these patches (environment‐induced mortality) and form dense clumps of immature palms. Competition on nutrient‐rich patches then favors the few juveniles that manage to survive farther from these patches (density‐dependent mortality). Finally, the last surviving juvenile of a clump suddenly experiences almost no competition with conspecifics, due to the long distance between clumps of juveniles, and owing to its root‐foraging ability, it can now recruit to the adult stage, subject only to senescence. Pattern variations among savanna facies are consistent with this scenario.

Sex-specific pattern of spatial genetic structure in dioecious and clonal tree species, Populus alba L.

“…This would mean that observed SSS could be induced with difference in microhabitat quality and not with clonality itself. In our opinion, SSS could be involved in generating sexspecific SGS because different microhabitats might be the source of different spatial patterns producing a differential course of demographic processes (Barot et al 1999) that stays in close relationship with population genetic structure.…”

Estrutura demográfica e padrão espacial de uma população natural de Araucaria angustifolia (Bertol.) Kuntze (araucariaceae), na Reserva Genética Florestal de Caçador, Estado de Santa Catarina

“…Para os testes de associação espacial entre a regeneração e os indivíduos femininos e a regeneração e os adultos, foi utilizada a Função K-bivariada (RIPLEY, 1977). Os envelopes foram construídos utilizando-se 99 simulações com arranjos toroidais (BAROT et al, 1999). Tanto as Funções K-univariada e K-bivariada quanto seus envelopes foram calculados, empregando-se algoritmos escritos no R (R DEVELOPMENT CORE TEAM, 2008) pacote splancs (ROWLINGSON e DIGGLE, 1993).…”

“…Inicialmente, muitos trabalhos têm utilizado a análise espacial apenas de maneira descritiva (BAROT et al, 1999), mas ela é importante ferramenta para inferir sobre processos ecológicos. O estudo do padrão espacial, além de ser o primeiro passo para espécies que não tenham estudos detalhados, permite gerar hipóteses sobre processos que dão origem a determinado padrão (DALE, 1999).…”

“…O estudo do padrão espacial, além de ser o primeiro passo para espécies que não tenham estudos detalhados, permite gerar hipóteses sobre processos que dão origem a determinado padrão (DALE, 1999). Um padrão pode ser resposta à heterogeneidade ambiental, interações intra e interespecíficas, como competição e predação, dispersão, crescimento, senescência, mortalidade e reprodução (JANZEN, 1970;BAROT et al, 1999;DALE, 1999;PERRY et al, 2002;AIBA et al, 2004;PALMIOTTO et al, 2004;STOLL e BERGIUS, 2005;RODRIGUES et al, 2007).…”

Demografia de Geonoma gamiova em área de extrativismo foliar

“…A distribuição espacial agregada encontrada na população estudada também é descrita para outras palmeiras clonais (BAROT et al, 1999, SVENNING, 2001. Essa característica, associada à alta densidade, pode subsidiar plantios e repovoamentos da espécie na área de estudo, dado que, para permitir a viabilidade econômica extrativa, sem prejudicar as demandas crescentes de mercado e causar impacto negativo ao ambiente, há necessidade de conservação da espécie, bem como a domesticação e o estabelecimento de unidades de cultivo (HOMMA, 2008).…”